Definition of Terms
The definitions found here pertain to the field of science involved with solution and colloid chemistry. Similar terms from other fields of science, such as nuclear science, are not applicable to solutions and colloids.
acid - A compound that dissociates to produce hydrogen (H+) cations when dissolved in water. See also pH. Acids in water solutions exhibit the following common properties: they taste sour; turn litmus paper red; and react with certain metals, such as zinc, to yield hydrogen gas. Acids can be classified as organic or inorganic. Some of the more common organic acids are: citric acid, carbonic acid, hydrogen cyanide, salicylic acid, lactic acid, and tartaric acid. Some of the common inorganic acids are: hydrogen sulfide, phosphoric acid, hydrogen chloride, and sulfuric acid.
activity - The activity of a dissolved species in solution is the "effective" concentration of that species.
In an "ideal" solution, the molecules in the solution do not interact with each other and the concentration and the activity are identical. This is the case for very dilute solutions. In a "real" solution, there is a certain interaction between the molecules resulting in a diminished "activity" of the molecules toward the outside world, and the solution behaves like it would contain lower concentration of the dissolved species than it actually does. The activity can be expressed as the product of an "activity coefficient" and the concentration. A plot of activity coefficient as a function of concentration for silver ions is shown here .
adsorption - 1) The formation of a layer of gas, liquid, or solid on the surface of a solid or, less frequently, of a liquid. There are two types depending on the nature of the forces involved. In chemisorption a single layer of molecules, atoms, or ions is attached to the adsorbent surface by chemical bonds. In physisorption adsorbed molecules are held by the weaker van der Waals' forces.
2) An increase of the concentration of a solute in the vicinity of a solid surface, over that in the bulk of the solution, due to the attractive interaction between the solid immersed into the solution and the solute . Adsorption on a solid from a gaseous phase also occurs. It is a surface process, not to be confused with absorption .
aggregation - Massing of materials together as in clumping. A clumped mass of material or small particles formed from individual atoms. Individual atoms in close proximity to other like atoms will be pulled together by van der Waals' force and form particles. At the level of individual atoms there is no counter force to prevent the formation of particles. In this regard the behavior of individual atoms differs from ions. In the case of ions, the ionic charge creates a mutual repulsion of the ions thus keeping the ions uniformly distributed in the fluid and preventing the formation of particles.
ampere - Measurement unit of current . Abbreviation: "A" or "amp".
anion – A negatively charged ion, i.e. an ion that is attracted to the anode in electrophoresis . The name is derived from anode ion. The negative charge results because there are more electrons than protons in the anion. Anions can be formed from nonmetals by reduction (see oxidation and reduction) or from neutral acids (see acids and bases) or polar compounds by ionization.
argyria - A discoloration of the skin wherein the skin turns a blue-grey color as a result of over exposure to certain forms of silver. Argyria is known to be caused by ingesting; 1) silver salts (compounds) such as silver nitrate, 2) high concentrations of ionic silver, 3) protein based silver products aka "silver protein" or "mild silver protein". Argyria is not caused by true silver colloids which consist of nanometer sized particles of silver in pure water. More ...
atom - The smallest part of an element that can exist chemically. Atoms consist of small dense nucleus of protons and neutrons surrounded by moving electrons . The number of electrons equals the number of protons so the overall charge is zero. The electrons are considered to move in circular or elliptical orbits or, more accurately, in regions of space around the nucleus.
atomic absorption spectroscopy (AAS) - An analytical technique in which a sample is vaporized causing the atoms to increase their energy state and absorb electromagnetic radiation at characteristic wavelengths. Used for trace metal (parts-per-million) and ultra trace metal (parts-per-billion) analysis of samples.
atomic number - The number of protons in the nucleus of a nuclide; all the atoms of a chemical element have the same atomic number; sometimes indicated by a subscript preceding the symbol of a chemical element (e.g., 1H). Symbol Z.
atomic weight (also known as the relative atomic mass) - The average atomic mass of an element compared to 1/12 the mass of carbon 12.
base - A compound that dissociates to produce hydroxyl (OH-) anions when dissolved in water (also called "caustic" or "alkali"). See also pH. Bases in water solutions exhibit these common properties: they taste bitter; turn litmus paper blue; and feel slippery. Bases can be classified as organic or inorganic. Some examples of organic bases are: pyridine and ethylamine. Some common inorganic bases are: sodium hydroxide, sodium carbonate, sodium bicarbonate, calcium hydroxide, and calcium carbonate.
Brownian motion - Chaotic motion of minute particle suspended in a gas or liquid. More ...
cation – A positively charged ion, i.e. an ion that is attracted to the cathode in electrophoresis . The name is derived from cathode ion. The charge results because there are more protons than electrons in the cation due to missing orbital electrons. Cations can be formed from a metal by oxidation (see oxidation and reduction), from a neutral base (see acids and bases) by protonation, or from a polar compound by ionization. Cationic species include Ag(+), Na(+), Mg(++), and NH(4+). The cations of the transition elements have characteristic colors in water solution. Salts are made up of cations and anions.
cell voltage - The electrical potential difference between the two electrodes of an electrochemical cell . In case of a three-electrode cell, the potential difference between the working electrode and the counter electrode.
charge transport - The phenomenon of movement (transportation) of electrical charge from one part of the system to another, occurring through electromigration .
chemical bond - mechanism whereby atoms combine to form molecules. There is a chemical bond between two atoms or groups of atoms when the forces acting between them are strong enough to lead to the formation of an aggregate with sufficient stability to be regarded as an independent species. The number of bonds an atom forms corresponds to its valence. The amount of energy required to break a bond and produce neutral atoms is called the bond energy. All bonds arise from the attraction of unlike charges according to Coulomb's law; however, depending on the atoms involved, this force manifests itself in quite different ways. The principal types of chemical bond are the ionic, covalent, metallic, and hydrogen bonds. The ionic and covalent bonds are idealized cases, however; most bonds are of an intermediate type.
coagulation - The process in which colloidal particles come together irreversible to form larger masses. Coagulation can be brought about by adding ions that change the ionic strength of the solution and thus destabilize the colloid.
Colloidal Science Laboratory (CSL) - The laboratory facility that performs the research, does the analysis and prepares the technical reports used on this web site. CSL is equipped with state of the art scientific equipment specifically developed for characterizing colloidal solutions. For more information see Laboratory Capabilities.
colloidal silver solution – A solution containing pure water and nanometer sized silver particles in a colloidal suspension. Most silver colloids also contain silver ions . Typically, the silver in ionic form constitutes 90% or more of the total silver in solution . If the solution contained all ions and no particles, it would be considered an ionic solution, not a colloid since there would be no particles suspended in the water. If the solution contained only particles and no ions, it would be considered a pure colloid. The particles remain suspended in the water owing to a particle charge which causes an electrostatic mutual repulsion of the particles. This particle charge is due to adsorption of ions from the surrounding solution and is called zeta potential .
colloid stability - The interaction of particles in polar liquids is not governed by the electrical potential at the surface of the particle, but by the effective potential of the particle and its associated ions . To utilize electrostatic control, it is the zeta potential of a particle that must be measured rather than its surface charge. Overall colloid stability depends on the interaction between individual particles. If mutual repulsion exists between particles in a colloid, the dispersant will resist flocculation . However, in the long term there may be caking or creaming through natural sedimentation . Attractive forces present in the dispersant will cause flocculation or coagulation to occur. Most stability problems may be approached by considering the balance between the repulsive and attractive forces. In practice there are two ways to achieve this balance: (1) Polymers may be added which adsorb on to the surface of the particles within the colloid causing repulsion by steric effects . (2) Alternatively, the ionic composition of the colloidal solution can be adjusted, with the change in distribution of charged species determining the stability of the colloid. Both methods have benefits depending on the application. Generally, a combination of electrostatic and steric effects is responsible for stability. More...
compound - A substance formed by the combination of elements in fixed proportions. The formation of a compound involves a chemical reaction; i.e. there is a change in the configuration of the valence electrons of the atoms . Compounds, unlike mixtures, cannot be separated by physical means. See also molecule .
conductivity cell - A cell specially designed for the measurement of the conductivity of an electrolyte solution . It is a small vessel containing two metallic electrodes , the cell is filled with the solution to be measured. Also called "conductance cell."
The measurement of the conductivity of an electrolyte solution is more complicated than a similar measurement with a metallic conductor. When measuring with dc current, one would have to take into consideration the electromotive force of the electrochemical cell , and the polarization of the electrodes. Therefore, the measurements are typically carried out with high frequency ac current and the electrodes in the conductivity cell are typically made of platinized platinum to avoid these complications. The cell geometry usually does not ensure that exactly and only one cubic centimeter of solution will carry the current; therefore, the cell has to be calibrated to obtain the specific conductance of the solution. The calibration is usually carried out with high purity potassium chloride solutions, and the resulting calibration constant is often called the "cell constant."
concentration - The measure of the amount of dissolved material ( solute ) in a solution . It can be expressed in a variety of ways. Expressions in weight percent, and grams of solute per liter of solution are common. A more fundamental way to express concentration is used in chemistry: the molar concentration. A solution is considered one molar (1 M) if it contains as many grams of solute per liter of solution as is the molecular weight of the solute (the so called gram-mol ). This provides an atomistically fundamental expression because one gram-mol of any material will contain the same (and very large) number of molecules . One gram-mol of hydrogen gas contains the exact same number of molecules as one gram-mol of table salt (sodium chloride), even though the latter is much heavier. In this dictionary, the term "concentration " always designates molarity unless otherwise specified.
current - The movement of electrical charges in a conductor ; carried by electrons in an electronic conductor and by ions in an ionic conductor . "By definition" the electrical current always flows from the positive potential end of the conductor toward the negative potential end, independent of the actual direction of motion of the differently charged current carrier particles. Two kinds of currents must be distinguished: "direct current (dc)" and "alternating current (ac)." Direct current is the unidirectional continuous flow of current, while alternating current is the oscillating (back and forth) flow of current. In electrochemistry, we almost always use direct current. Consequently, the term "current" always designates "dc" in this dictionary unless specifically stated to be "ac." The normal household current is an alternating current.
diffusion - The movement of chemical species (ions or molecules ) under the influence of concentration difference. The species will move from the high concentration area to the low concentration area till the concentration is uniform in the whole phase. Diffusion in solutions is the most important phenomenon in electrochemistry, but diffusion will occur also in gases and solids.
dipole - A pair of equal and opposite electrical charges separated by a small distance. A dipole will align itself, if possible, in the presence of other electrical charges according to the attraction of opposite and repulsion of like charges. Externally neutral chemical molecules can have a dipole inside; for example, water is a triangular molecule with the oxygen at one corner and the two hydrogens at the other two corners. The internal charge distribution is such that the hydrogen side has a slight excess of positive charge and the oxygen end is correspondingly negative. A dipole is characterized by its "dipole moment," the product of the charge and the separation distance (coulomb times centimeter).
dispersant - Something that disperses. A chemical substance added to a dispersion capable of maintaining the dispersed particles in suspension .
dispersion - 1) The act of scattering or separating; the condition of being scattered. 2) the incorporation of the particles of one substance into the body of another, comprising solutions , suspensions , and colloid solutions. 3) a colloid solution.
dissociation - The process that may occur when a chemical compound is dissolved in a solvent (e.g., water). The molecules of the compound will break up ("dissociate") into two or more ions resulting in an ionically conducting electrolyte solution; for example, the common table salt (sodium chloride) will dissociate into a single charged sodium cation and a single charged chloride anion .
electrical conductivity - The measurement of electrical conductivity is generally referred to as just conductivity. Conductivity is the reciprocal of the resistivity of a material. When a fluid is involved, the electrolytic conductivity is given by the ratio of current density to the electric field strength. The conductance of a sample of pure water depends on how the measurement was made. Things that affect conductance include how big a sample is being measured, how far apart the electrodes are, etc. Conductance is defined as the reciprocal of the resistance in ohms, measured between the opposing faces of a 1 cm cube of liquid at a specific temperature. The unit of conductance is called Siemens (S) which was formerly named the mho (ohm spelled backward). Because a measurement gives the conductance, methods have been devised to convert the measured value to the conductivity, so that results can be compared from different experiments. This requires that a cell constant (K) be determined for the instrument using a solution of known conductivity. Once the cell constant has been determined, then the conductivity can be calculated as follows:
Conductivity = Cell conductance x K
The cell constant is related to the physical characteristics of the measuring cell. K is defined for two flat, parallel measuring electrodes as the electrode separation distance (d) divided by the electrode area (A). Thus, for a 1 cm cube of liquid, K = d/A, where A=1 cm-1
The unit of conductivity is Siemens/m or in scaled form Siemens/cm. In modern conductivity meters, the measured cell value is entered into the meter and the conversion from conductance to conductivity is performed automatically. The instrument scales the value and displays the results in micro-Siemens/cm (uS/cm).
An approximation of the concentration of ionic silver in solution (ppm) may be determined from the conductivity.
electrical energy - A form of energy . It expresses the ability of an electrical source to carry out useful work or generate heat; for example, this energy can be used to drive an electrical motor and carry out some mechanical work, or to generate heat with an electrical heater. The electrical energy is usually expressed in units of watt-hour, symbol: "Wh".
electrical potential - The electrical potential difference between two point in a circuit is the cause of the flow of a current . It is somewhat analogous to the difference in height in a waterfall that causes the water to fall, or the difference in pressure in a pipeline that causes the gas to flow. In electrochemistry we typically cannot measure "absolute" potentials, only the "difference" of potential between two points. For similar concepts, see electromotive force (emf) and voltage . These terms are sometimes used interchangeably. However, in electrochemistry "emf" usually refers to the potential difference between the two electrodes of an electrochemical cell when there is no current flowing through the cell, "voltage" refers to same with current flowing, and "potential" is usually used in connection with electrodes .
electric double layer - The liquid layer surrounding the particle exists as two parts; an inner region (Stern layer) where the ions are strongly bound and an outer (diffuse) region where they are less firmly associated. More ...
electrochemical cell - A device that converts chemical energy into electrical energy or vice versa when a chemical reaction is occurring in the cell. Typically, it consists of two metal electrodes immersed into an aqueous solution (electrolyte ) with electrode reactions occurring at the electrode-solution surfaces.
electrode - The two electronically conducting parts of an electrochemical cell. See also anode and cathode . These can be simple metallic structures (rods, sheets, etc.) or much more complicated, composite structures. E.g., the electrodes in a rechargeable battery will also "contain" the chemicals being converted during its operation. The term "electrode " is also used to denote complex assemblies that include an electrode in a small vessel, which contains an electrolyte and is equipped with an ion-permeable separator. Reference electrodes are such assemblies.
electrode potential - The electrical potential difference between an electrode and a reference electrode. We cannot measure the "absolute" potential of an electrode; therefore, the electrode potential must always be referred to an "arbitrary zero point," defined by the potential of the reference electrode . Consequently, it is very important always to
electrolysis - A process that decomposes a chemical compound or produces a new compound by the action of an electrical current . The electrical current is passed through an electrolytic cell and oxidation/reduction reactions occur at the electrodes ; for example, water can be decomposed into hydrogen and oxygen by electrolysis.
electrolyte - A chemical compound (salt, acid, or base) that dissociates into electrically charged ions when dissolved in a solvent. The resulting electrolyte (or electrolytic) solution is an ionic conductor of electricity. Very often, the so formed solution itself is simply called an "electrolyte."
electrolytic cell - An electrochemical cell that converts electrical energy into chemical energy. The chemical reactions do not occur "spontaneously" at the electrodes when they are connected through an external circuit. The reaction must be forced by applying an external electrical current. It is used to store electrical energy in chemical form. It is also used to decompose or produce (synthesize) new chemicals by application of electrical power. This process is called electrolysis , for example, water can be decomposed into hydrogen gas and oxygen gas.
electromotive force (emf) - The cell voltage of a galvanic cell measured when there is no current flowing through the cell. In other words, the equilibrium electrode potential difference between the two electrodes of the cell.
electron - An elementary particle with a rest mass of 9.1093897 X 10-31 kg and a negative charge of 1.60217733 X 10-19 coulomb . Electrons are present in all atoms in groupings called shells around the nucleus; when they are detached from the atom they are called free electrons. The outermost electrons of an atom determine its chemical and electrical properties. An atom may combine chemically with another atom in various ways, either by giving up or receiving electrons, thus setting up an electrical attraction between the atoms (see ion ), or by sharing one or more pairs of electrons. Because metals have few outermost electrons and tend to give them up easily, they are good conductors of electricity or heat.
electronic conductor - A material that conducts electricity with electrons as charge carriers.
electronvolt - Symbol eV. A unit of energy equal to the work done on an electron in moving it through a potential difference of one volt. It is used as a measure of particle energies although it is not an SI unit . 1 eV = 1.602 X 10-19 joule.
electrophoresis – A technique for the analysis and separation of colloids, based on the movement of charged colloidal particles in an electric field. There are various experimental methods. In one the sample is placed in a U-tube and buffer solution added to each arm, so there are sharp boundaries between the buffer and the sample. An electrode is placed in each arm, a voltage applied, and the motion of the boundaries under the influence of the field is observed. The rate of migration of the particles depends on the field, the charge on the particles, and on other factors such as the size and shape of the particles.
In modern zeta potential instruments an electrophoresis capillary tube contains the colloid sample and the voltage is applied to electrodes at each end of the tube. The rate of migration and the direction of movement of the particles are measured by Laser Doppler Velocimetry .
element – A substance that cannot be decomposed into simpler substances. In an element, all the atoms have the same number of protons and electrons , although the number of neutrons may vary. There are 92 naturally occurring elements.
elemental silver - This is a scientific term referring to silver in its natural state as a metallic element. The atoms must contain all 47 orbital electrons making the atom complete as a metallic element in its pure state and having no ionic charge. Silver ions are missing one orbital electron, thus contain 46 orbital electrons, have a positive ionic charge, are not metallic, and therefore are not considered elemental silver.
energy - The energy of a system expresses the ability of that system to do some useful work or generate heat. Energy can be in many forms; for example, mechanical energy, chemical energy, heat energy, electrical energy, etc. The different forms of energy can be converted into each other.
It is a fundamental law of nature that energy can never be converted from one form to another 100%, some of the energy is always converted into heat energy during the conversion. Also, heat can never be converted 100% into any other form of energy.
equilibrium - An electrode or an electrochemical cell is said to be in "equilibrium" when there is no net current flowing and there are no net electrode reactions taking place in the system. In equilibrium, the potential of the electrodes is the equilibrium potential and the cell voltage is the electromotive
equilibrium electrode potential - The electrical potential of an electrode measured against a reference electrode when there is no current flowing trough the electrode. In other words, the electromotive force of an electrochemical cell consisting of the electrode in question and a reference electrode. See also equilibrium .
The concept of equilibrium potential is probably easiest to demonstrate with a simple metal/metal-ion electrode system. When a metal (e.g., silver) is immersed in a solution containing its ion (e.g., silver nitrate solution) metal ions will cross the metal/solution interface. They will pass from the phase where the "chemical energy" of the ion is large to the phase where the "chemical energy" of the ion is smaller. Depending on the system, this can occur in either direction. However only the positively charged (e.g., silver) cations can pass through the interface. The negatively charged electrons cannot pass into the solution, and the anions (e.g., nitrate) cannot pass into the metal. Consequently, charge accumulation occurs at the interface forming an electrical double layer . Consider an example when the metal ions move preferentially from the metal into the solution: the metal surface becomes negatively charged because of the accumulation of the electrons left behind, while the solution layer near the metal surface becomes positively charged because of the accumulation of silver ions. This process produces a potential difference between the two phases that will slow and eventually stop the passage of the metal ions. At "equilibrium" the chemical driving force and the opposing electrical force are equal. The potential difference between the metal and the solution phases under these conditions is the "equilibrium potential difference." This potential difference cannot be measured because there is no way to make an electrical connection to the solution phase without setting up another electrode potential. Consequently, electrode potentials are always measured against a reference electrode whose potential is known on an arbitrary scale. See standard hydrogen electrode .
flocculation - The process in which particles in a colloid aggregate into larger clumps. Often, the term is used for a reversible aggregation of particles in which the forces holding the particles together are weak and the colloid can be redispersed by agitation.
fugacity - The expression of "activity" for a component in a mixture of gases. It has the same physical meaning as the activity for a component in a solution.
gram-mol - An amount of a compound equal in grams to its molecular weight . For example, the molecular weight of water is 18, so 18 grams of water is called a gram-mol of water. This provides an atomistically fundamental unit because one gram-mol of any material will contain the same (and very large) number of molecules . One gram-mol of hydrogen gas contains the exactly same number of molecules as one gram-mol of table salt (sodium chloride), even though the latter is much heavier.
hadron - Any elementary particle that is subject to the strong interaction . Hadrons are subdivided into baryons and mesons.
According to Chemistry International Vol 23, No.6 November 2001 - "Heavy Metals" - A Meaningless Term
Over the past two decades, the term "heavy metals" has been used increasingly in various publications and in legislation related to chemical hazards and the safe use of chemicals. It is often used as a group name for metals and semimetals (metalloids) that have been associated with contamination and potential toxicity or ecotoxicity. At the same time, legal regulations often specify a list of heavy metals to which they apply. Such lists may differ from one set of regulations to the other, or the term may be used without specifying which heavy metals are covered. In other words, the term "heavy metals" has been used inconsistently. This practice has led to general confusion regarding the significance of the term. The inconsistent use of the term "heavy metals" reflects inconsistency in the scientific literature. It is, therefore, necessary to review the usage that has developed for the term, paying particular attention to its relationship to fundamental chemistry. Without care for the scientific fundamentals, confused thought is likely to prevent advances in scientific knowledge and to lead to bad legislation and to generally bad decision-making.
Def 1.) A generalized definition in common use: One of 23 chemical elements that has a specific gravity (a measure of density) at least five times that of water.
Def 2.) Definition according to OSHA - The term "Heavy Metals" is generally interpreted to include those metals from periodic table groups IIA through VIA. The semi-metallic elements boron, arsenic, selenium, and tellurium are often included in this classification. At trace levels, many of these elements are necessary to support life. However, at elevated levels they become toxic, may build up in biological systems, and become a significant health hazard.
Def 3.) Definition used by many - The term heavy metal refers to any metallic chemical element that has a relatively high density and is toxic, highly toxic or poisonous at low concentrations. Examples of heavy metals include mercury (Hg), cadmium (Cd), arsenic (As), chromium (Cr), thallium (Tl), and lead (Pb).
Heavy metals are dangerous because they tend to bioaccumulate. For example, marine organisms can consume a particularly dangerous form of mercury called methyl mercury. When fish eat these organisms, the methyl mercury is not excreted, but retained in bodily tissues. The older the fish and the more contaminated organisms it has consumed, the greater the amount of methyl mercury in its tissues. When another fish eats the first fish, the accumulated methyl mercury is passed up the food chain, eventually becoming hundreds or thousands of times its original concentration. Any organism at the top of the food chain (humans, polar bears etc.) faces a serious risk of mercury poisoning by eating such fish.
More on heavy metals here...
hydrodynamic boundary layer - A thin immobile layer of fluid that always exists at a solid/moving-fluid interface. Whether the movement of the fluid is due to "forced" or "natural" convection, a thin layer of fluid will always remain completely immobile at the surface of the solid due to the solid-liquid interactive forces.
ion - 1) An atom or radical having a charge of positive (cation ) or negative (anion ) electricity owing to the loss (positive) or gain (negative) of one or more electrons. Substances that form ions are called electrolytes . 2) An atomic or molecular particle having a net electric charge.
In the field of nuclear science, any atomic object whose weight is greater or equal to an electron is considered a particle. This definition of an atomic particle is not applicable to the field of solution or colloid chemistry.
ionic charge – A positive or negative electric charge possessed by an ion as a result of the gain or loss of one or more orbital electrons . Silver ions always possess a positive ionic charge due the loss of a single electron. Ionic charge is responsible for the electrostatic repulsion that causes ions to remain dispersed in a liquid.
ionic conductor - A material that conducts electricity with ions as charge carriers. See also electrolyte .
ionic mobility - A quantitative measure of an ion's ability to move under the influence of a potential difference in solution. (See also electromigration .) It is the speed of movement under the influence of unit potential difference.
ionic silver - A solution consisting of water and silver ions (dissolved silver). Contains no silver particles and does not exhibit a Tyndall Effect . Is an ionic conductor and the electrical conductivity is directly related to the ionic concentration . The ions in solution remain dispersed due to mutual repulsion created by the ionic charge . Has a metallic taste which is quite pronounced in high concentrations. When the water is evaporated the solids that remain consist of silver compounds such as silver carbonate and silver hydroxide depending on what anions where in solution with the silver. Silver hydroxide reduces to silver oxide and hydrogen. Silver carbonate reduces to silver oxide and carbon dioxide.
ion-selective electrode (ISE) - An electrode or electrode assembly with a potential that is dependent on the concentration of an ionic species in the test solution and is used for electroanalysis. Ion-selective electrodes are often membrane type electrodes.
isotonic solution - A solution which is adjusted so that the osmotic pressure is the same as in a reference fluid, such as a body fluid. A salt solution listed as isotonic would have its osmotic pressure adjusted to be the same as blood or siliva, depending on the intended use. An isotonic saline solution would generally contain 6.5 mg of sodium chloride (salt) per liter of DI water.
Mesocopper® - Registered trademarked name of a copper colloid consisting of mesoparticles of 0.9999 pure copper suspended in pure deionized water. Mesocopper is produced by the mesoprocess and is characterized as having particles that are typically less than 2 nm in diameter.
Mesogold® - Registered trademarked name of a gold colloid consisting of mesoparticles of 0.9999 pure gold suspended in pure deionized water. Mesogold is produced by the mesoprocess and is characterized as having particles that are typically less than 2 nm in diameter.
mesoparticle - Very small particles whose size is greater than an atom but smaller than conventional small particles. Size ranges from sub-nanometer to 10 nanometers in diameter and typically consist of 10 - 30,000 atoms per particle. Mesoparticles may be produced by first reducing the element to its monoatomic state and then coalescing particles from the individual atoms.
Mesoprocess(TM) - The mesoprocess is an advanced proprietary process developed at Colloidal Science Laboratory, Inc. that produces metal colloids consisting of mesoparticles . The process produces colloids whose particles are typically less than 2 nm in diameter.
Mesosilver®- Registered trademarked name of a silver colloid consisting of mesoparticles of 0.9999 fine silver suspended in pure deionized water. Mesosilver is produced by the mesoprocess and is characterized as having a high percentage of the total silver content contained in particles that are typically less than 2 nm in diameter.
molar concentration - See concentration .
molecule – One of the fundamental units forming a chemical compound ; the smallest part of a chemical compound that can take part in a chemical reaction. In most covalent compounds, molecules consist of groups of atoms held together by covalent or coordinate bonds. Ionic compounds do not have single molecules, being collections of oppositely charged ions.
mutual repulsion – A force that disperses ions and particles having a like charge. For ions , the charge that cause the repulsive force is ionic charge . Ions in solution are dispersed uniformly throughout the solution by this repulsive force. For particles it is the zeta potential that results from adsorbed ions in the solution. In a colloid, mutual repulsion is the force that maintains the stability of the colloid. It is the force that counters the attractive force that would cause flocculation .
nanometer (nm) - A billionth of a meter (10-9 meters). A nanometer is the unit of measure used to measure the wavelength of visible light. For example, the thickness of a human hair is approximately 76,200 nanometers or 3 thousandths of an inch. Particles sizes in silver colloids are expressed in nanometers.
neutron - A neutral hadron that is stable in the atomic nucleus but decays into a proton , an electron , and antineutrino with a mean life of 12 minutes outside the nucleus. Its rest mass is slightly greater than that of the proton, being 1.6749286 X 10 -27 kg. Neutrons occur in all atomic nuclei except normal hydrogen.
N.I.S.T. - The National Institute of Standards and Technology, formerly known as the National Bureau of Standards. Founded in 1901, NIST is a non-regulatory federal agency within the U.S. Commerce Department's Technology Administration. NIST's mission is to develop and promote measurement, standards, and technology to enhance productivity, facilitate trade, and improve the quality of life.
ORME - An acronym for Obitally Rearranged M onoatomic Element. ORMEs were discovered by David Hudson who holds worldwide patents on eleven ORMEs which represent a new form of matter. ORMEs are atoms of elements whose orbital electrons have been altered from the energy state as it normally exists in the element. ORMEs exist for certain transition and noble metal elements, specifically, gold, silver, copper, cobalt, nickel, and the six platinum group elements, i.e., platinum, palladium, rhodium, iridium, ruthenium, and osmium. The materials are stable, non-metallic-like forms of the described transition and noble metal elements, and have a previously unknown electron orbital rearrangement in the "d", "s", and vacant "p" orbitals. The electron rearrangement bestows upon the monoatomic elements unique electronic, chemical, magnetic, and physical properties.
An ORME has the same number of neutrons , protons , and electrons as the normal element but the physical properties are dramatically different because the electrons have been rearranged and become stable at an increased energy state. ORMEs will produce different atomic absorption/emission spectral lines than normal elements which make their presence difficult to detect using atomic absorption/emission based spectroscopy. Mass spectroscopy techniques such as ICP-MS which are based on the mass/charge ratios of the neutrons and protons in the nucleus of the atom remain unaffected by the rearranged orbital electrons and are able to detect the ORMEs.
osmosis - The difussion of a fluid through a semi permeable membrane.
osmotic pressure - The pressure in atmospheres or mm of Hg (Torr) required to prevent osmosis.
oxidation and reduction - complementary chemical reactions characterized by the loss or gain, respectively, of one or more electrons by an atom or molecule. Originally the term oxidation was used to refer to a reaction in which oxygen combined with an element or compound, e.g., the reaction of magnesium with oxygen to form magnesium oxide or the combination of carbon monoxide with oxygen to form carbon dioxide. Similarly, reduction referred to a decrease in the amount of oxygen in a substance or its complete removal, e.g., the reaction of cupric oxide and hydrogen to form copper and water. When an atom or molecule combines with oxygen, it tends to give up electrons to the oxygen in forming a chemical bond . Similarly, when it loses oxygen, it tends to gain electrons. Such changes are now described in terms of changes in the oxidation number, or oxidation state, of the atom or molecule (see valence ). Thus oxidation has come to be defined as a loss of electrons or an increase in oxidation number, while reduction is defined as a gain of electrons or a decrease in oxidation number, whether or not oxygen itself is actually involved in the reaction.
particle charge – A charge imparted to the particle due to adsorption of ions from the surrounding solution . The charge is produced at the slipping plane surrounding the particle and is called the zeta potential . Particle behavior in an electric field is determined by its zeta potential.
particle concentration - A measure of the amount of metal contained in the particles found in a colloid. An important property in determining the particle surface area . Particle surface area increases as particle concentration increases. Particle concentration is expressed in parts-per-million (PPM) of metal contained in the particles.
particle size distribution - An important property of colloidal solutions. The distribution of particle sizes of a colloid is determined by measurement using Photon Correlation Spectroscopy (PCS). Such measurement provides a histogram type plot whose x-axis is size in nanometers and y-axis shows the percentage of particles of that size. The data is presented in tabular format as well. The most appropriate type of size distribution for silver colloids is a distribution plot based on the volume of silver contained in the particles for each size bin.
particle surface area (cm2/mL) - Total surface area in square centimeters (cm2) of all the particles in one milli-liter(mL) of colloid. The surface area is a calculated value based on the concentration of particles (ppm) and the mean diameter of the particles. The mean diameter is determined from the volume analysis of the Particle Size Report generated by the Malvern Photon Correlation Spectrometer. If the volume analysis consists of more that one peak, then total surface area is calculated as a weighted sum of the surface areas of the mean particle diameters at the peaks. The calculation assumes the particles are spherical. Particle surface area is inversely proportional to particle size, which means for a constant concentration of particles, the surface area increases as the particle size decreases. For example, the particle surface area of 1 ppm of particles having a mean diameter of 10 nm is 0.423 cm2/mL, while 1 ppm of 1 nm diameter particles has a particle surface area of 4.229 cm 2/mL.
Particle surface area serves as a metric for comparing different colloidal solutions. In the chemical world, reactivity increases with increasing surface area. Therefore, the effectiveness of colloidal solutions increases with decreasing particle size.
pH - A measure of the acidity/alkalinity (basicity) of a solution . The pH scale extends from 0 to 14 (in aqueous solutions at room temperature). A pH value of 7 indicates a neutral solution. A pH value of less than 7 indicates an acidic solution, the acidity increases with decreasing pH value. A pH value of more than 7 indicates a basic solution, the basicity or alkalinity increases with increasing pH value.
The pH of a solution is equal to the negative, ten-based logarithm of the activity of the hydrogen ions in the solution. Neutral water dissociates into equal amounts of hydrogen (H+) cations and hydroxyl (OH-) anions . As the product of the concentrations (activities) of the two ions is always a constant 10-14 , pure water has a pH of 7. In acidic solutions the hydrogen ions are in excess, while in basic solutions the hydroxyl ions are in excess.
Photon Correlation Spectroscopy(PCS) - A technique to measure the size of particles dispersed in fluid by collecting data from scattered laser light from a sample maintained at a precise temperature. The instrument is a Photon Correlation Spectrometer and is designed for characterizing particles size and zeta potential of colloidal solutions. Particles dispersed in a fluid are in constant random motion - Brownian motion . The speed of movement is dependent on the size of the particle, as well as temperature and other variables such as viscosity. The speed of particle movement is measured by analyzing the scattered light, and the particle size is determined from the speed. The PCS is probably the single most important tool available for characterizing particles in colloids. The Malvern Zetasizer 3000HSA is the PCS used at the Colloidal Science Laboratory to make these measurements.
polychromatic - Electromagnetic radiation that consists of a mixture of different wavelengths (i.e. white light that contains all the colors of the rainbow). This need not refer only to visible radiation.
polymer - A substance having large molecules formed by the joining of smaller molecules, referred to as monomers. There are number of natural polymers, such as polysaccharides. Protein polymers can be derived from animal collagen (gelatin), dairy (casein and whey) and grains (gluten). Synthetic polymers are extensively used in plastics. Polymers do not have a definite formula since they consist of chains of different lengths. Polymers are used as surfactants to stabilize colloids by steric effect .
proton - An elementary particle the is stable, bears a positive charge equal to an in magnitude to that of the electron , and has a mass of 1.672614 X 10-27 kg, which is 1836.12 time that of an electron. The proton is a hydrogen ion and occurs in all atomic nuclei.
reference electrode - An electrode that has a well known and stable equilibrium electrode potential . It is used as a reference point against which the potential of other electrodes (typically that of the working electrode or measuring electrode) can be measured in an electrochemical cell . In principle it can be any electrode fulfilling the above requirements. In practice, there are a few commonly-used (and usually commercially available) electrode assemblies that have an electrode potential independent of the electrolyte used in the cell. Some common reference electrodes include, the silver/silver-chloride electrode, calomel electrode, and hydrogen electrode.
Strictly speaking, there can be a small change in the potential of these electrodes depending on the electrolyte because the presence of a liquid-junction potential. This is very often (justifiably or not) ignored. The liquid-junction potential is also minimized by the use of high concentration potassium chloride as the filling solution of the reference electrodes, because the diffusion rate of both ions is very closely the same in these solutions.
salt - chemical compound (other than water) formed by a chemical reaction between an acid and a base. The most familiar salt is sodium chloride , the principal component of common table salt. Sodium chloride, NaCl, and water, H2O, are formed by neutralization of sodium hydroxide, NaOH, a base, with hydrogen chloride, HCl, an acid. Most salts are ionic compounds (see chemical bond ); they are made up of ions rather than molecules. The chemical formula for an ionic salt is an empirical formula; it does not represent a molecule but shows the proportion of atoms of the elements that make up the salt. The formula for sodium chloride, NaCl, indicates that equal numbers of sodium and chlorine atoms combine to form the salt. In the reaction of sodium with chlorine, each sodium atom loses an electron, becoming positively charged, and each chlorine atom gains an electron, becoming negatively charged (see oxidation and reduction); there are equal numbers of positively charged sodium ions and negatively charged chloride ions in sodium chloride. The ions in a solid salt are usually arranged in a definite crystalline structure, each positive ion being associated with a fixed number of negative ions, and vice versa.
saturated - 1) (of a compound ) Consisting of molecules that have only single bonds (i.e. no double or triple bonds). Saturated compounds can undergo substitution reactions but not addition reactions. 2) (of a solution ) Containing the maximum equilibrium amount of solute at a given temperature. In a saturated solution the dissolved substance is in equilibrium with the undissolved substance; i.e. the rate at which solute particles leave the solution is exactly balanced by the rate at which they dissolve. A solution containing less than the equilibrium amount is said to be unsaturated. One containing more than the equilibrium amount is supersaturated. Supersaturated solutions can be made by slowly cooling a saturated solution. Such solutions are metastable; if a small crystal seed is added the excess solute crystallizes out of solution.
sedimentation - The settling of the solid particles through a liquid either to produce a concentrated slurry from a dilute suspension or to clarify a liquid containing solid particles. Usually this relies on the force of gravity, but if the particles are too small or the difference between the solid and liquid phase is too small, a centrifuge may be used.
serum - 1) The clear portion of any body fluid; the clear fluid moistening serous membranes. 2) Blood serum; the clear liquid that separates from blood on clotting. The cell-free portion of the blood from which the fibrinogen has been separated in the process of clotting.
silver atom (Ag) – The smallest part of elemental silver that can exist chemically. Atoms consist of a small dense nucleus of protons and neutrons surrounded by moving electrons . The number of electrons equals the number of protons so the overall charge is zero. The electrons are considered to move in circular or elliptical orbits, or more accurately, in regions of space around the nucleus. The size of a silver atom is 0.288 nm in diameter. Silver has an atomic number of 47, which means it has 47 protons in the nucleus and 47 electrons orbiting the nucleus. Silver has an atomic weight of 108.8682. Silver atoms do not contribute to the electrical conductivity of solutions that contain them. Adding silver atoms to the solution does not increase the conductivity. Silver is not soluble in water and does not combine readily to form compounds .
silver chloride (AgCl)- A compound of silver formed when silver ions (cations ) combine with chloride ions (anions ). A single molecule of silver choride is produced when a single silver ion combines with a single chloride ion. Silver chloride molecules are draw to each other by van der Waals' force of attraction to form every larger particles.
silver ion (Ag+) – An ion of silver is formed when a single electron is removed from a silver atom causing the ion to have a positive charge. An ion that has a positive charge is attracted to the cathode and is referred to as a cathode ion or cation . Silver ions are water-soluble and exist only in the presence of water or other solvent . Silver ions diffuse through a solution due to the mutual repulsion they have for each other caused by their ionic charge . Silver ions exist as individual entities in solution and do not cluster together to form particles like atoms. A silver ion is a different form of matter than an atom of silver and has entirely different physical properties. While an ion possesses ionic charge owing to the missing electron, it is not considered an atom of silver with a charge. Ionic charge is caused by the missing electron and is different from particle charge that is caused by adsorption of ions on the surface of the particle. If the water containing silver ions is evaporated, the ions are forced to combine with anions present in the solution and will thus become a silver compound when the water is removed. The silver compound(s) produced is determined by the anions present in the solution before the water is removed. Silver ions do contribute to the electrical conductivity of solutions that contain them. Adding silver ions to the solution does increase the conductivity. Silver ions are soluble in water and do combine readily to form compounds.
silver particles – Particles are clusters of silver atoms . The size of the particles found in a colloid can range in size from less than 1 nanometer (nm) to 1000 nm. The size of the particles typically found in silver colloids is under 100 nm. The atoms in a silver particle remain held together by van der Waals’ force of attraction that causes like (identical) atoms to be attracted to each other. A particle 1 nm in diameter consists of 31 silver atoms, a particle 10 nm in diameter consists of about 31000 atoms and a particle 20 nm in diameter consists of about 250,000 atoms. Silver particles do not contribute to the electrical conductivity of solutions that contain them. Adding silver particles to the solution does not increase the conductivity. For more information on the attributes of silver particles see Attributes of Silver Particles .
silver protein - Also know as "mild silver protein", is a combination of metallic silver particles suspended in a protein solution. While various protein binders may be used, the protein most commonly used is an animal protein called gelatin. Gelatin is obtained by boiling the skin, tendons, and ligaments of animals. As a result, it contains protein, collagen (a primary component of joints, cartilage, and nails), and various amino acids. Gelatin is widely known by the trade name Knox Gelatin. Gelatin is water soluble and will remain in liquid form provided a sufficient amount of water is present. Most products claiming to be high concentrations of colloidal silver, typically in the range of 30 to10,000 ppm are in fact silver protein colloids. While some of these products are labeled as Silver Protein or Mild Silver Protein, many such products are simply labeled as colloidal silver and the word protein does not appear anywhere on the label or in the product advertising literature. Silver protein products generally have very large silver particles. For these metallic silver particles to remain suspended in water, they need additional buoyancy to keep from sinking. This is why the gelatin is added. The gelatin molecules will encapsulate each particle of silver and add enough buoyancy so that it does not sink to the bottom. It is analogous to tying a balloon to a brick to keep the brick from sinking. Due to the high concentration of large silver particles these products are known to cause argyria, a condition that causes the skin to turn blue-gray. Because of the large size of the silver particles these products have very low particle surface area.
Three characteristics of silver protein products are:
For more information on silver protein, see The Truth About Silver Protein
silver solution - A solution consisting of ionic silver (silver dissolved in water), but without metallic silver particles . A silver solution is not colloidal silver since no particles are present. Many products claiming to be colloidal silver are technically silver solutions since the entire silver content is in the form of silver ions and they do not contain silver particles.
SI unit - Any of the units of the Système International d'Unités, or International System of Units, adopted in 1960 at the Eleventh General Conference of Weights and Measures. SI units are based on the metric system and many are derived from natural constants.
slipping plane - A notional boundary at the diffuse (second layer) of ions surrounding a particle dispersed in a liquid is known as the hydrodynamic boundary layer. The plane at this boundary is the surface of hydrodynamic shear, or the slipping plane. The potential at this boundary is known as the zeta potential .
solvation - Ions in solution are always surrounded by solvent molecules . A few of these molecules will be more or less strongly attached to the ion (mainly because of the attraction of the charged ion and the dipole of the solvent molecule) and this assembly may be considered as a single unit for some purposes. E.g., the solvent molecules will move together with the ion during diffusion and electromigration . The number of solvent molecules so attached to an ion is called the solvation number. The surface of an electrode also can, and usually is, solvated. Since the electrodes usually have some excess charge (see electrical double layer ,) they also attract the solvent dipoles, and the electrode surface is usually covered by a monolayer of strongly oriented solvent molecules.
The solvation number is not very exactly defined since its value may depend on the measurement technique.
solubility - The maximum amount of a species that can be dissolved in a given solvent. It is usually expressed as the maximum achievable concentration . A solution is called "saturated" if it contains the maximum dissolvable amount.
solubility product - The solubility of slightly soluble salts is often expressed as the product of the solubility concentrations of its ions . For example, the solubility product of silver chloride is the product of the concentrations of the silver and chloride ions in the saturated solution of this salt. The significance of the solubility product is that its value cannot be exceeded even in the presence of other dissolved salts. Consequently, the solubility of silver chloride is less in a solution containing potassium chloride than in pure water. This is because in the calculation of the solubility product one must use the "total" chloride concentration in the solution, therefore a silver concentration lower than in water is needed to satisfy a constant solubility product.
The solubility (the saturated solution concentration) of the salt, in the absence of any other dissolved species in the solution, is the square root of the solubility product for a salt like the silver chloride. Strictly speaking, activities should be used instead of concentrations.
solute - The dissolved species (e.g., a salt) in a solution .
solution - A homogeneous mixture of a liquid (the solvent ) with a gas or solid (the solute ). In a solution, the molecules of the solute are discrete and mixed with the molecules of the solvent. There is usually some interaction between the solvent and the solute molecules (see solvation ). Two liquids that can mix on the molecular level are said to be miscible . In this case, the solvent is the major component and the solute is the minor component.
solvent - A liquid that dissolves another substance or substances to form a solution . Polar solvents are compounds such as water and liquid ammonia, which have dipole moments and consequently high dielectric constants. These solvents are capable of dissolving ionic compounds or covalent compounds that ionize (see solvation ). Nonpolar solvents are compounds such as ethoxyethane and benzene, which do not have permanent dipole moments. These do not dissolve ionic compounds but will dissolve nonpolar covalent compounds. Solvents can be further categorized according to their proton-donating and accepting properties. Amphiprotic solvents self-ionize and can therefore act as both a proton donators and acceptors. A typical example is water. Aprotic solvents neither accept nor donate protons; tetrachloromethane (carbon tetrachloride) is an example.
specific conductance - The quantitative and characteristic measure of the conductivity of a given substance. This characteristic constant is the numerical value of the conductivity between two opposite sides of a unit cube (usually a cube of one centimeter) of the substance. Also called specific conductivity .
standard hydrogen electrode (SHE) - The most fundamental reference electrode in electrochemistry. "By definition" its equilibrium potential is considered zero at any temperature, because this electrode was chosen as an arbitrary zero point for electrode potentials . A zero point is needed since the potential of a single electrode cannot be measured, only the difference of two electrode potentials is measurable. All electrode potentials are expressed on this hydrogen scale . It is a hydrogen electrode with an electrolyte containing unit concentration of hydrogen ions and saturated with hydrogen gas at unit atmosphere pressure. This electrode can be somewhat inconvenient to use because of the need to supply hydrogen gas. Therefore, other reference electrodes (e.g., calomel or silver/silver chloride) are often used instead, but the measured electrode potentials can be converted to the hydrogen scale. Also called normal hydrogen electrode.
steric effect - An effect in which the rate or path of a chemical reaction depends on the size or arrangement of groups in a molecule. More ...
transmission electron microscopy (TEM) - A form of microscope that uses a beam of electrons instead of a beam of light (as in an optical microscope) to form a large image of a very small object. In optical microscopes the resolution is limited by the wavelength of the light. High-energy electrons, however, can be associated with a considerably shorter wavelength than light; for example, electrons accelerated to an energy of 105 electronvolts have a wavelength of 0.004 nanometers enabling a resolution of 0.2 - 0.5 nm to be achieved. The transmission electron microscope has an electron beam, sharply focused by electron lenses, passing through a very thin specimen onto a fluorescent screen, where a visual image is formed. This image can be photographed.
When used to observe colloidal silver solutions, the sample must be desiccated to remove the water. This removal of water forces the silver ions in solution to combine with anions in solution to form silver compounds. This dramatically changes what was in solution so that what is observed using the TEM now has little relationship to what was in the solution before desiccation. For this reason, the interpretation of TEM images of ionic solutions becomes difficult in the extreme.
The TEM is sometimes used in an attempt to measure the size of particles in solution. The U.S. National Bureau of Standards (now N.I.S.T) has determined that it would required at least 10,000 TEM images be analyzed in order to make a statistically valid measurement of particle size based on TEM images. For this reason, the TEM is not considered viable for measuring particle sizes.
true colloidal silver (true silver colloid) - This term is refers to silver colloids whose silver content consist mainly of silver nanoparticles. The particle content must be greater than 50% of the total silver content to qualify as a true silver colloid. True silver colloids will always exhibit an apparent color, usually amber, because the nanoparticles absorb light energy from the visible spectrum typically at a wavelength around 400 nm. The amber color is the complement of the absorbed wavelength. The highest quality true silver colloids will appear as clear amber colored liquids without any noticeable turbidity (cloudiness).
transition elements - or transition metals, in chemistry, group of elements characterized by the filling of an inner d electron orbital as atomic number increases. This includes the elements from titanium to copper, and those lying in the columns below them in the periodic table . Many of the chemical and physical properties of the transition elements are due to their unfilled d orbitals. In the elements of the lanthanide series and the actinide series the inner f orbital is filled as atomic number increases; those elements are often called the inner transition elements. Transition elements generally exhibit high density, high melting point, magnetic properties, variable valence, and the formation of stable coordination complexes. Their variable valence is due to the electrons in the d orbitals. The study of the complex ions and compounds formed by transition metals is an important branch of chemistry. Many of these complexes are highly colored and exhibit paramagnetism.
total silver - This refers to a measurement of a silver colloid that includes the silver content of the particles which is metallic silver and the silver ions which are in solution (dissolved). In addition to particles and ions, silver present in the form of silver compounds would also be included in the measurement of total silver. High quality silver colloids contain almost no silver compounds.
turbidity - Cloudiness or opaqueness of water due to suspended particles in the water causing a reduction in the transmission of light. Turbidity is measured by passing a beam of light through the sample and detecting the scattered light at 90-degrees from the incident light. The unit of measure is the Nephelometric Turbidity Unit (NTU) which is numerically the same as a Formazin Turbidity Unit (FTU). Calibration of the turbidimeter is by standards of known turbidity consisting of formazin solutions. For colloidal silver solutions the turbidity measurement provides a relative metric for Tyndall effect. Particles in solution affect Tyndall effect but ions do not.
Tyndall effect (TE) - The scattering of light as is passes through a medium containing small particles. If a polychromatic beam of light is passed through a medium containing particles less than about one-twentieth of the wavelength of light, the scattered light appears blue. This accounts for blue appearance of tobacco smoke. At higher particle diameters, the scattered light remains polychromatic. The effect is seen in suspensions and metal colloids. For comparative purposes, Tyndall effect can be quantified by measuring the sample turbidity . Named after John Tyndall (1820-1893).
uncertainty principal (Heisenberg uncertainty principal; principal of indeterminism) - The principal that it is not possible to know with unlimited accuracy both the position and momentum of a particle. This principal was discovered in 1927 by Werner Heisenberg (1901-76). The uncertainty arises because in order to locate the position of a particle exactly, an observer must be able to bounce off it a photon of radiation; this act of location itself alters the position of the particle in an unpredictable way. In other words, the act of observation alters that which is being observed.
valence - combining capacity of an atom expressed as the number of single bonds the atom can form or the number of electrons an element gives up or accepts when reacting to form a compound. Atoms are called monovalent, divalent, trivalent, or tetravalent, according to whether they form one, two, three, or four bonds (see chemical bond).
van der Waals’ force – An attractive force between atoms and molecules, named after J. D. van der Waals (1837-1923). The force accounts for the term a/V2 in van der Waals’ equation. These forces are much weaker than those arising from valence bonds are inversely proportional to the seventh power of the distance between the atoms or molecules . There are three factors causing such forces: 1) dipole-dipole interaction, i.e. electrostatic attractions between two molecules with permanent dipole moments; 2) dipole-induced dipole interactions, in which the dipole of one molecule polarizes a neighboring molecule; 3) dispersion forces arising because of small instantaneous dipoles in atoms. When the distance separating individual atoms is only a few atomic diameters, the force of attraction can exceed 100,000 G-forces.
In a colloid, this attractive force would cause flocculation of the particles if it were not for the force of mutual repulsion that counters this attractive force thus causing the colloid to be stable.
zeta potential - Zeta potential is a measure of the magnitude of the repulsion or attraction between particles. Most particles in a polar medium such as water will possess a surface charge. A charged particle will attract ions of the opposite charge in the dispersant , forming a strongly bound layer close to the surface of the particle. Those ions further away from the core particle make up a diffuse layer, more loosely bound to the particle. Within this diffuse layer is a notional boundary, inside which the particle and its associated ions act as a single entity, diffusing through the dispersion together.
The plane at this boundary is known as the surface of hydrodynamic shear, or the slipping plane . The potential at this boundary is known as the zeta potential. It is important to note that the magnitude of the zeta potential is affected by both the nature of the surface of the particle, and the composition of the dispersant . Zeta potential is affected by pH. More ...
Zeta potential is an important property of colloidal solutions and is essential to the understanding of colloid stability . The zeta potential of silver colloidal solutions has been measured to be between –15 mV to –60 mV. More ...
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