Glossary: Simple compounds

acetate. (CH₃COO^-, C₂H₃O₂^-) acetate ion.

1. an ion formed by removing the acidic hydrogen of acetic acid, HC₂H₃O₂. 2. a compound derived by replacing the acidic hydrogen in acetic acid. 3. A fiber made of cellulose acetate.

acetic acid (CH₃COOH, HC₂H₃O₂) ethanoic acid; vinegar acid; methanecarboxylic acid.

A simple organic acid that gives vinegar its characteristic odor and flavor. Glacial acetic acid is pure acetic acid.

acid. ([Lat. acidus, sour]) Compare with base.

1. a compound which releases hydrogen ions (H⁺) in solution (Arrhenius). 2. a compound containing detachable hydrogen ions (Bronsted-Lowry). 3. a compound that can accept a pair of electrons from a base (Lewis)..

addition compound. complex compound. Compare with hydrate.

An addition compound contains two or more simpler compounds that can be packed in a definite ratio into a crystal. A dot is used to separate the compounds in the formula. For example, ZnSO₄·7 H₂O is an addition compound of zinc sulfate and water. This represents a compound, and not a mixture, because there is a definite 1:7 ratio of zinc sulfate to water in the compound. Hydrates are a common type of addition compound.

alkaline earth.

An oxide of an alkaline earth metal, which produces an alkaline solution in reaction with water.

alkane. paraffin. Compare with hydrocarbon and alkene.

A series of organic compounds with general formula C_nH_2n+2. Alkane names end with -ane. Examples are propane (with n=3) and octane (with n=8).

ammonia. (NH₃) Compare with ammonium.

Pure NH₃ is a colorless gas with a sharp, characteristic odor. It is easily liquified by pressure, and is very soluble in water. Ammonia acts as a weak base. Aqueous solutions of ammonia are (incorrectly) referred to as "ammonium hydroxide".

ammonium ion. (NH₄⁺) ammonium.

NH₄⁺ is a cation formed by neutralization of ammonia, which acts as a weak base.

anhydrous. anhydrous compound; anhydride. Compare with hydrate.

A compound with all water removed, especially water of hydration. For example, strongly heating copper(II) sulfate pentahydrate (CuSO₄·5H₂O) produces anhydrous copper(II) sulfate (CuSO₄).

anion. Compare with cation.

An anion is a negatively charged ion. Nonmetals typically form anions.

base. alkali; alkaline; basic. Compare with acid.

1. a compound that reacts with an acid to form a salt. 2. a compound that produces hydroxide ions in aqueous solution (Arrhenius). 3. a molecule or ion that captures hydrogen ions.(Bronsted-Lowry). 4. a molecule or ion that donates an electron pair to form a chemical bond.(Lewis).

binary compound. Compare with compound.

A compound that contains two different elements. NaCl is a binary compound; NaClO is not.

Brösted acid. Compare with acid.

A material that gives up hydrogen ions in a chemical reaction.

Brösted base. Compare with base.

A material that accepts hydrogen ions in a chemical reaction.

cation. Compare with anion.

A cation is a positively charged ion. Metals typically form cations.

chemical bond. bond; bonding; chemical bonding.

A chemical bond is a strong attraction between two or more atoms. Bonds hold atoms in molecules and crystals together. There are many types of chemical bonds, but all involve electrons which are either shared or transferred between the bonded atoms.

covalent bond. covalent; covalently bound. Compare with covalent compound and ionic bond.

A covalent bond is a very strong attraction between two or more atoms that are sharing their electrons. In structural formulas, covalent bonds are represented by a line drawn between the symbols of the bonded atoms.

covalent compound. molecular compound. Compare with ionic bond and ionic compound.

A compound made of molecules- not ions. The atoms in the compound are bound together by shared electrons. Also called a molecular compound.

cupric. (Cu²⁺) cupric ion.

Deprecated. 1. the copper(II) ion, Cu²⁺. 2. A compound that contains copper in the +2 oxidation state.

cuprous. (Cu⁺) cuprous ion.

Deprecated. 1. the copper(I) ion, Cu⁺. 2. A compound that contains copper in the +1 oxidation state.

diatomic molecule. Compare with binary compound and polyatomic molecule.

A molecule that contains only two atoms. All of the noninert gases occur as diatomic molecules; e. g. hydrogen, oxygen, nitrogen, fluorine, and chlorine are H₂, O₂, N₂, F₂, and Cl₂, respectively.

efflorescent. efflorescence; efflorescing. Compare with deliquescent and hygroscopic.

Efflorescent substances lose water of crystallization to the air. The loss of water changes the crystal structure, often producing a powdery crust.

element Compare with compound and mixture.

An element is a substance composed of atoms with identical atomic number. The older definition of element (an element is a pure substance that can't be decomposed chemically) was made obsolete by the discovery of isotopes.

empirical formula. simplest formula. Compare with molecular formula.

Empirical formulas show which elements are present in a compound, with their mole ratios indicated as subscripts. For example, the empirical formula of glucose is CH₂O, which means that for every mole of carbon in the compound, there are 2 moles of hydrogen and one mole of oxygen.

ferric. ferric ion.

Deprecated. 1. the iron(III) ion, Fe³⁺. 2. A compound that contains iron in the +3 oxidation state.

ferrous. ferrous ion.

Deprecated. 1. the iron(II) ion, Fe²⁺. 2. A compound that contains iron in the +2 oxidation state.

formula weight. formula mass. Compare with molecular weight and empirical formula.

The formula weight is the sum of the atomic weights of the atoms in an empirical formula. Formula weights are usually written in atomic mass units (u).

formula unit. Compare with empirical formula.

One formula weight of a compound.

halide. halide ion.

A compound or ion containing fluorine, chlorine, bromine, iodine, or astatine.

hydrate. Compare with addition compound.

A hydrate is an addition compound that contains water in weak chemical combination with another compound. For example, crystals of CuSO₄·5 H₂O (copper sulfate pentahydrate) are made of regularly repeating units, each containing 5 molecules of water weakly bound to a copper(II) ion and a sulfate ion.

hydrazine. (NH₂NH₂)

A colorless, fuming, corrosive liquid that is a powerful reducing agent. NH₂NH₂ is used in jet and rocket fuels, and as an intermediate in the manufacture of agricultural, textile, photographic, and industrial chemicals.

hydrocarbon. Compare with alkane, alkene, alkyne, and organic.

Hydrocarbons are organic compounds that contain only hydrogen and carbon. The simplest hydrocarbons are the alkanes.

hydronium ion. (H₃O⁺) hydronium.

The H₃O⁺ ion, formed by capture of a hydrogen ion by a water molecule. A strong covalent bond is formed between the hydrogen ion and water oxygen; all hydrogen ions in aqueous solution are bound inside hydronium ions.

hydroxide. (OH^-) hydroxide ion. Compare with hydroxyl.

1. The OH^- ion. 2. Compounds containing the OH^- ion. See also: hydroxide compounds.

hygroscopic.

Able to absorb moisture from air. For example, sodium hydroxide pellets are so hygroscopic that they dissolve in the water they absorb from the air.

hygroscopicity.

The ability of a substance to absorb moisture from air. For example, sodium hydroxide pellets are so hygroscopic that they dissolve in the water they absorb from the air.

inorganic compound. inorganic. Compare with organic.

A compound that does not contain carbon chemically bound to hydrogen. Carbonates, bicarbonates, carbides, and carbon oxides are considered inorganic compounds, even though they contain carbon.

ionic bond. ionically bound; ionic bonding. Compare with covalent bond.

An attraction between ions of opposite charge. Potassium bromide consists of potassium ions (K⁺) ionically bound to bromide ions (Br^-). Unlike covalent bonds, ionic bond formation involves transfer of electrons, and ionic bonding is not directional.

ionic compound. salt. Compare with covalent compound and ionic bond.

A compound made of distinguishable cations and anions, held together by electrostatic forces.

IUPAC

International Union of Pure and Applied Chemistry, an organization which sets international standards for chemical nomenclature, atomic weights, and the names of newly discovered elements.

law of conservation of mass.

There is no change in total mass during a chemical change. The demonstration of conservation of mass by Antoine Lavoisier in the late 18th century was a milestone in the development of modern chemistry.

law of definite proportions.

When two pure substances react to form a compound, they do so in a definite proportion by mass. For example, when water is formed from the reaction between hydrogen and oxygen, the 'definite proportion' is 1 g of H for every 8 g of O.

law of multiple proportions.

When one element can combine with another to form more than one compound, the mass ratios of the elements in the compounds are simple whole-number ratios of each other. For example, in CO and in CO₂, the oxygen-to-carbon ratios are 16:12 and 32:12, respectively. Note that the second ratio is exactly twice the first, because there are exactly twice as many oxygens in CO₂ per carbon as there are in CO.

molecular formula. formula; chemical formula. Compare with empirical formula.

A notation that indicates the type and number of atoms in a molecule. The molecular formula of glucose is C₆H₁₂O₆, which indicates that a molecule of glucose contains 6 atoms of carbon, 12 atoms of hydrogen, and 6 atoms of oxygen.

molecular model stick model; ball and stick model; spacefilling model.

A representation of a molecule. The model can be purely computational or it can be an actual physical object. Stick models show bonds, ball-and-stick models show bonds and atoms, and spacefilling models show relative atomic sizes.

molecular weight. molecular mass. Compare with formula weight and molecular formula.

The average mass of a molecule, calculated by summing the atomic weights of atoms in the molecular formula. Note that the words mass and weight are often used interchangeably in chemistry.

nomenclature.

A system for naming things. For example, "organic nomenclature" is the system used to name organic compounds.

octane. (C₈H₁₈) Compare with alkane and hydrocarbon.

Flammable liquid compounds found in petroleum and natural gas. There are 18 different octanes- they have different structural formulas but share the molecular formula C₈H₁₈. Octane is used as a fuel and as a raw material for building more complex organic molecules. It is the eighth member of the alkane series.

organic. organic compound. Compare with inorganic compound.

Compounds that contain carbon chemically bound to hydrogen. They often contain other elements (particularly O, N, halogens, or S). Organic compounds were once thought to be produced only by living things. We now know that any organic compound can be synthesized in the laboratory (although this can be extremely difficult in practice!)

polyatomic ion. Compare with molecule, ion and polyatomic molecule.

A polyatomic ion is a charged particle that contains more than two covalently bound atoms. See Polyatomic Ions for more.

polyatomic molecule. Compare with polyatomic ion and diatomic molecule.

A polyatomic molecule is an uncharged particle that contains more than two atoms.

propane. (C₃H₈) Compare with alkane and hydrocarbon.

A colorless, odorless, flammable gas, found in petroleum and natural gas. It is used as a fuel and as a raw material for building more complex organic molecules. Propane is the third member of the alkane series.

proton donor. acid. Compare with base.

Because a free H⁺ ion is technically a bare proton, acids are sometimes referred to as "proton donors" because they release hydrogen ions in solution. The term "proton donor" is misleading, since in aqueous solution, the hydrogen ion is never a bare proton- it's covalently bound to a water molecule as an H₃O⁺ ion. Further, acids don't "donate" protons; they yield them to bases with a stronger affinity for them.

stoichiometry.

1. Ratios of atoms in a compound. 2. Ratios of moles of compounds in a reaction. 3. A branch of chemistry that quantitatively relates amounts of elements and compounds involved in chemical reactions, based on the law of conservation of mass and the law of definite proportions.

structural formula. Compare with molecular formula and empirical formula.

A structural formula is a diagram that shows how the atoms in a molecule are bonded together. Atoms are represented by their element symbols and covalent bonds are represented by lines. The symbol for carbon is often not drawn. Most structural formulas don't show the actual shape of the molecule (they're like floor plans that show the layout but not the 3D shape of a house).

sugar.

A carbohydrate with a characteristically sweet taste. Sugars are classified as monosaccharides, disaccharides, or trisaccharides.

superoxide. superoxide ion.

A binary compound containing oxygen in the -½ oxidation state. For example, KO₂ is potassium superoxide, an ionic compound containing the superoxide ion, O₂^-.

thio-.

A prefix that means, "replace an oxygen with sulfur". For example, sulfate ion is SO₄^2-; thiosulfate ion is S₂O₃^2-. Cyanate ion is OCN^-; thiocyanate ion is SCN^-.

water of crystallization. water of hydration.

Water that is stoichiometrically bound in a crystal; for example, the waters in copper sulfate pentahydrate.

Copyright © 1997-2010 by Fred Senese
Comments & questions to fsenese@frostburg.edu
Last Revised 02/23/18.URL: http://antoine.frostburg.edu/chem/senese/101/compounds/glossary.shtml