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Glossary of Chemical Terms

Chemistry is the science of substances—what they look like, what they do and why. It isn't just a subject for scientists in laboratories, surrounded by bottles and beakers.

This glossary of chemical terms is intended as a resource so that you can better understand how chemistry affects every aspect of your daily life.



Absorption: The action of a solid or liquid in taking up and retaining another substance uniformly throughout its internal structure.

ABS Resin: A type of thermoplastic synthetic co-polymer composed of various proportions of styrene, acrylonitrile and butadiene.

Acid: A compound, either inorganic or organic, that (1) reacts with a metal to evolve hydrogen; (2) reacts with a base to form a salt; (3) dissociates in water solution to yield hydrogen (or hydronium) ions; (4) has a pH of less than seven (7); and (5) neutralizes bases or alkaline media by receiving a pair of electrons from the base so that a covalent bond is formed between the acid and the base.

Adsorption: Attachment of the molecules of a gas or liquid to the surface of another substance (normally a solid).

Aerobic: Requiring the presence of air or oxygen to live, grow and reproduce.
Aliphatic: Refers to a major series of organic compounds whose carbon atoms are arranged in straight or branched chains.

Alkali: A term normally used to refer to hydroxides and carbonates of the metals of Group IA of the Periodic Table, as well as to ammonium hydroxide.

Alloy: A mixture or solution of metals, either solid or liquid, which may or may not include a nonmetal.
Anhydrous: Without water. A substance in which no water is present in the form of a hydrate or water of crystallization.

Anion: A negatively charged ion.

Anode: The positive electrode in an electrolytic cell.

Aqueous: A solution or suspension in which the solvent is water.

Aromatic: A major series of unsaturated cyclic hydrocarbons whose carbon atoms are arranged in closed rings.

Asbestos: Fibrous magnesium silicate.

Atomic Number: The number of protons or positively charged mass units in the nucleus of an atom, upon which its structure and properties depend.

Autoignition Point: The lowest temperature at which a material will catch fire without the aid of a flame or spark.

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Base: A substance that (1) liberates hydroxyl ions when dissolved in water; (2) that liberates negative ions of various kinds in any solvent; (3) that receives a hydrogen ion from a strong acid to form a weaker acid; (4) that gives up two electrons an acid, forming a covalent bond with the acid.

Baumé: A scale introduced by the French chemist, Antoine Baumé, for use in determining the specific gravity of liquids.

Brix: A density scale used chiefly in the sugar industry to indicate the sucrose concentration a solution.

Buffer: An acid-base balancing or control reaction which the pH of a solution is protected from major change when acids or bases are added to it.

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Carbonate: A compound formed by the reaction of carbonic acid with either a metal or an organic compound.

Carcinogen: Any substance which has been found to induce the formation of cancerous tissue in experimental animals.

Catalyst: An element or compound that accelerates the rate of a chemical reaction but is neither changed or consumed by it.

Cathode: The negative electrode of an electrolytic cell.

Cation: An ion having one or more positive charges.

Caustics: Strong alkalis—their solutions being corrosive to the skin and other tissues.
Caustic Soda: Sodium hydroxide.

Centigrade: The temperature scale universally used by scientists in which the freezing point of water is represented by 0°C and its boiling point by 100°C; it is also called Celsius, after its inventor, Anders Celsius.

Chemotherapy: The development and use of chemical compounds that are specific for the treatment of diseases.

Chocolate: Theobroma oil.

Colorimetry: An analytical method by which the amount of a compound in solution can be determined by measuring the strength of its color by either visual or photometric methods.

Combustible Material: A term usually applied to materials which ignite above 65°C and burn relatively slowly.

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Decomposition: A type of chemical reaction in which one compound divides or splits into two or more simpler substances.

Denaturant: A substance added to ethyl alcohol to prevent its being used for internal consumption.

Denier: A term used in the textile industry to designate the weight per unit length of a filament.

Density: The ratio of weight (mass) to volume of any substance; usually expressed as grams per cubic centimeter.

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Elastomer: A term coined about 1935, when synthetic rubber-like materials were introduced on a commercial scale, to describe any high polymer having the essential properties of vulcanized natural rubber.

Electrochemistry: That portion of chemistry concerned primarily with the relationship between electrical forces and chemical reactions.

Electrode: A material used in an electrolytic cell to enable the current to enter or leave the solution.

Electrolysis: Decomposition of a chemical compound by means of an electric current.

Electron: A particle of negative electricity.

Emulsion: A permanent suspension or dispersion, usually of oil particles in water.

Endothermic: A term used to characterize a chemical reaction which requires absorption of heat from an external source.

End Point: That point in a titration at which no further addition of titrating solution is necessary.

Exothermic: A term used to characterize a chemical reaction that gives off heat as it proceeds.

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Fahrenheit: The temperature scale commonly used in the U. S.; the freezing point of water is 32°F and the boiling point is 212°F at sea level.

Flame Retardant: A substance applied to or incorporated in a combustible material to reduce eliminate its tendency to ignite when exposed a low-energy flame.

Flash Point: The temperature at which an organic liquid evolves a high enough concentration vapor at or near its surface to form an ignitable mixture with air.

Fluorocarbon: Any of a broad group of organic compounds analogous to hydrocarbons in which all most of the hydrogen atoms of a hydrocarbon have been replaced by fluorine. Some types also contain chlorine and are called chlorofluorocarbons or CFCs.

Flux: Any material or substance that will reduce the melting or softening temperature of another material when added to it.

FRP: Fiberglass-reinforced plastic.

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Galvanizing: Application of a protective layer of zinc to a metal, chiefly steel, to prevent or inhibit corrosion.

Glacial: A term applied to a number of acids, which, in a highly pure state, have a freezing point slightly below room temperature.

Gram: A standard unit of mass (weight) equivalent to 1/453.49 pound.

GRAS: Generally Recognized as Safe—referring to those food additives that meet the requirements of the Food and Drug Administration.

Gravimetric: A term used by analytical chemists to denote methods of quantitative analysis that depend upon the weight of the components in the sample.

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Halogen: A term, whose literal meaning is “saltmaker"; refers to the five elements of Group VIIA of the Periodic Table—fluorine, chlorine, bromine, iodine and astatine.

Humidity (relative): The ratio of the amount of water vapor present in air at a given temperature to the maximum that can be held by air at that temperature, i.e., saturation.

Hydrocarbon: Any compound composed of carbon and hydrogen.

Hydrophilic: A term that refers to substances that tend to absorb and retain water.

Hydrophobic: A term that describes substances which repel water.

Hygroscopic: A term used to describe solid or liquid materials which pick up and retain water vapor from the air.

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Immiscible: A term used to describe substances of the same phase that cannot be uniformly mixed or blended.

Inert: Having little or no chemical affinity or activity.

Inhibitor: Any substance that retards or reduces the rate of a chemical reaction.

Inorganic: This term refers to a major and the oldest branch of chemistry—it is concerned with substances which do not contain carbon.

Ion: An atom, group or molecule that has either lost one or more electrons or gained one or more electrons.

Isomer: One of two or more compounds having the same molecular weight and formula, but often having quite different properties and somewhat different structure.

Isotope: Any of two (2) or more forms of an element in which the weights differ by one or more mass units due to a variation in the number of neutrons in the nuclei.

IUPAC: Abbreviation for International Union of Pure and Applied Chemistry.

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Kaolin: The most widely used industrial type of clay (aluminum silicate).

Ketone: A class of unsaturated and reactive compounds whose formula is characterized by a carbonyl group to which, two organic groups are attached.

Kinetic energy: The energy that a particle or an object possesses due to its motion or vibration.

Kjeldahl: An analytical method for determination of nitrogen in certain organic compounds.

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Lacquer: A type of organic coating in which rapid drying is effected by evaporation of solvents.

Liter: A standard unit of volume for gases and liquids.

—lysis: A suffix commonly used in chemical terminology derived from the Greek, meaning “to free" or “to loosen".

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Mass: Refers to the amount of material substance present in a body, irrespective of gravity.

Meter: A standard unit of length equivalent to 39.375 inches.

Micron: A unit of length in the metric system equivalent to one-millionth of a meter.

Molecular Weight: The total obtained by adding together the weights of all the atoms present in a molecule.

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Naptha: Any of several liquid mixtures of hydrocarbons of specific boiling and distillation ranges derived from either petroleum or coal tar.

Neutralization: The reaction between equivalent amounts of an acid and a base to form a salt.

Neutron: An uncharged nuclear particle.

NMR: Nuclear magnetic resonance.

Nomenclature: The names of chemical substances and the system used for assigning them.

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Octane Number: An arbitrary value denoting the antiknock rating of a gasoline.

Oleum: Alternative name for fuming sulfuric acid, i.e., sulfuric acid mixed with sulfur trioxide.

Optical Fiber: An extremely fine-drawn glass fiber of exceptional purity that will transmit laser light impulses with high fidelity.

Order of Magnitude: A term used in science to indicate a range of values representing numbers, dimensions, distances, etc., which start at any given value and ends at 10 times that value.

Organic: Any compound containing the element carbon.

Oxidation: The reverse of reduction. A reaction in which electrons are transferred from one atom to another—either in the uncombined state or within a molecule.

Oxidation Number: For a given element, the number of electrons it can transfer to another element with which it combines.

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Pasteurization: Heat treatment of liquid or semi-liquid food products for the purpose of killing or inactivating disease-causing bacteria.

Periodic Law: It states that the arrangement of electrons in the atoms of any given chemical element, and the properties determined by this arrangement, are closely related to the atomic number of that element. As the atomic number increases from one element to the next, the arrangement of electrons changes in a regularly repeated sequence.

Periodic Table: A systematic classification of the chemical elements based on the Periodic Law.
pH: A scale indicating the acidity or alkalinity of aqueous solutions.

Photochromic: This term denotes a material to which has been added a low percentage of light-sensitive chemical, the effect of which is to cause the material to darken in the presence of strong light and to resume its original transparency when the light intensity is decreased.

Poise: The standard unit for the viscosity of a fluid.

Potash: Potassium hydroxide.

Proton: The basic unit of mass that is a constituent of the nucleus of all elements, the number present being the atomic number of a given element.

Pyrolysis: A chemical change brought about by heat alone.

Pyrophoric: This term denotes a substance that ignites in air at or below room temperature without supply of heat, friction or shock.

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Qualitative Analysis: Examination of a sample of a material to determine the kinds of substances present and to identify each constituent.

Quantitative Analysis: Examination of a sample of a material to determine the amount or percentage of its constituents.

Quicklime: Calcium oxide.

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Reagent: Any chemical compound used in laboratory analyses to detect and identify specific constituents of the material being examined.

Reduction: The reverse of oxidation. The gaining of or acceptance of one or more electrons from another substance.

Resin: Naturally occurring water-insoluble mixtures of carboxylic acids, essential oils and other substances formed in numerous varieties of trees and shrubs.

Reversible: A chemical reaction which can proceed first to the right and then to the left when the conditions change.

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Salt: One of the products resulting from a reaction between an acid and a base.

Solvent: This term designates a liquid which can reduce certain solids or liquids to molecular or ionic form by relaxing the intermolecular forces that unite them.

Stoichiometry: Study of the mathematics of the material and energy balances (equilibrium) of chemical reactions.

STP: Conventional abbreviation for standard temperature and pressure.

Synergism: A phenomenon often encountered in chemistry in which one or more properties of a mixture are affected to a far greater extent that would be indicated by adding the values for the components taken individually.

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Tare: A weight used in analytical work to offset the weight of a container.

Titration: A volumetric means of finding the amount of a given substance in a solution.

Trace Elements: This term refers to five elements necessary for plant nutrition which are present in the soil in minute concentrations—boron, copper, manganese, molybdenum and zinc.

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Valance: A whole number indicating for any element its ability to combine with another element.
VCM: Abbreviation for vinyl chloride monomer.

Viscosity: The property of a liquid which causes it to resist flow or movement in response to external force applied to it.

VM&P Naphtha: Abbreviation for Varnish Makers and Painters naphtha.

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Wood Alcohol: Methyl alcohol.

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Please Note: The information contained in this publication is intended for general information purposes only. This publication is not a substitute for review of the applicable government regulations and standards, and should not be construed as legal advice or opinion. Readers with specific questions should refer to the cited regulation or consult with an attorney.

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