Key Terms

Acid A substance that produces H(aq) ions in aqueous solution. Strong acids ionize completely or almost completely in dilute aqueous solution. Weak acids ionize only slightly.

Acid-base reaction See Neutralization reaction.

Active metal A metal that readily loses electrons to form cations.

Activity series A listing of metals (and hydrogen) in order of decreasing activity.

Alkali metals Elements of Group IA in the periodic table, except hydrogen.

Alkaline earth metals Group IIA elements in the periodic table.

Atomic number The number of protons in the nucleus of an atom of an element.

Base A substance that produces OH(aq) ions in aqueous solution. Strong bases are soluble in water and are completely dissociated. Weak bases ionize only slightly.

Binary acid A binary compound in which H is bonded to a nonmetal in Group VIIA or a nonmetal other than oxygen in Group VIA.

Binary compound A compound consisting of two elements; may be ionic or molecular.

Chemical periodicity The variation in properties of elements with their positions in the periodic table.

Combination reaction Reaction in which two substances (elements or compounds) combine to form one compound.

Decomposition reaction Reaction in which a compound decomposes to form two or more products (elements, compounds, or some combination of these).

Displacement reaction A reaction in which one element displaces another from a compound.

Disproportionation reaction A redox reaction in which the oxidizing agent and the reducing agent are the same element.

Dissociation In aqueous solution, the process in which a solid ionic compound separates into its ions.

Electrolyte A substance whose aqueous solutions conduct electricity.

Formula unit equation An equation for a chemical reaction in which all formulas are written as complete formulas.

Gas-formation reaction A metathesis reaction in which an insoluble or slightly soluble gas is formed as a product.

Group (family) The elements in a vertical column of the periodic table.

Halogens Group VIIA elements in the periodic table.

Ionization In aqueous solution, the process in which a molecular compound separates to form ions.

Metal An element below and to the left of the stepwise division (metalloids) of the periodic table; about 80% of the known elements are metals.

Metalloids Elements with properties intermediate between metals and nonmetals: B, Si, Ge, As, Sb, Te, Po, and At.

Metathesis reaction A reaction in which the positive and negative ions in two compounds “change partners,” with no change in oxidation numbers, to form two new compounds.

Net ionic equation An equation that results from canceling spectator ions from a total ionic equation.

Neutralization reaction The reaction of an acid with a base to form a salt. Often, the reaction of hydrogen ions with hydroxide ions to form water molecules.

Noble (rare) gases Elements of Group VIIIA in the periodic table.

Nonelectrolyte A substance whose aqueous solutions do not conduct electricity.

Nonmetals Elements above and to the right of the metalloids in the periodic table.

Oxidation An increase in oxidation number; corresponds to a loss of electrons.

Oxidation numbers Arbitrary numbers that can be used as mechanical aids in writing formulas and balancing equations; for single-atom ions they correspond to the charge on the ion; less metallic atoms are assigned negative oxidation numbers in compounds and polyatomic ions.

Oxidation–reduction reaction A reaction in which oxidation and reduction occur; also called a redox reaction.

Oxidation states See Oxidation numbers.

Oxidizing agent The substance that oxidizes another substance and is reduced.

Period The elements in a horizontal row of the periodic table.

Periodic law The properties of the elements are periodic functions of their atomic numbers.

Periodic table An arrangement of elements in order of increasing atomic number that also emphasizes periodicity.

Periodicity Regular periodic variations of properties of elements with atomic number (and position in the periodic table).

Precipitate An insoluble solid that forms and separates from a solution.

Precipitation reaction A reaction in which a solid (precipitate) forms.

Pseudobinary ionic compound A compound that contains more than two elements but is named like a binary compound.

Redox reaction See Oxidation–reduction reaction.

Reducing agent The substance that reduces another substance and is oxidized.

Reduction A decrease in oxidation number; corresponds to a gain of electrons.

Reversible reaction A reaction that occurs in both directions; described with double arrows (34).

Salt A compound that contains a cation other than H and an anion other than OH or O2.

Semiconductor A substance that does not conduct electricity at low temperatures but does so at higher temperatures.

Spectator ions Ions in solution that do not participate in a chemical reaction. They do not appear in net ionic equations.

Strong acid An acid that ionizes (separates into ions) completely, or very nearly completely, in dilute aqueous solution.

Strong electrolyte A substance that conducts electricity well in dilute aqueous solution.

Strong base Metal hydroxide that is soluble in water and dissociates completely in dilute aqueous solution.

Ternary acid A ternary compound containing H, O, and another element, usually a nonmetal.

Ternary compound A compound consisting of three elements;may be ionic or molecular.

Total ionic equation An equation for a chemical reaction written to show the predominant form of all species in aqueous solution or in contact with water.

Weak acid An acid that ionizes only slightly in dilute aqueous solution.

Weak base A molecular substance that ionizes only slightly in water to produce an alkaline (base) solution.

Weak electrolyte A substance that conducts electricity poorly in dilute aqueous solution.