Acids and Bases - Key terms
A substance that, in its edible form, is sour to the taste, and in non-edible forms, is often capable of dissolving metals. Acids and bases react to form salts and water. These are all phenomenological definitions, however, in contrast to the three structural definitions of acids and bases—the Arrhenius, Brønsted-Lowry, and Lewis acid-base theories.
A term referring to the soluble hydroxides of the alkali and alkaline earth metals. Once "alkali" was used for the class of substances that react with acids to form salts; today, however, the more general term base is preferred.
An adjectival term used to identify the degree to which a substance displays the properties of a base.
The negatively charged ion that results when an atom gains one or more electrons. "Anion" is pronounced "AN-ie-un".
A substance in which water constitutes the solvent. A large number of chemical reactions take place in an aqueous solution.
ARRHENIUS ACID-BASE THEORY:
The first of three structural definitions of acids and bases. Formulated by Swedish chemist Svante Arrhenius (1859-1927), the Arrhenius theory defines acids and bases according to the ions they produce in an aqueous solution: an acid produces hydrogen ions (H + ), and a base hydroxide ions (OH − ).
A substance that, in its edible form, is bitter to the taste. Bases tend to be slippery to the touch, and in reaction with acids they produce salts and water. Bases and acids are most properly defined, however, not in these phenomenological terms, but by the three structural definitions of acids and bases—the Arrhenius, Brønsted-Lowry, and Lewis acid-base theories.
BRØNSTED-LOWRY ACID-BASE THEORY:
The second of three structural definitions of acids and bases. Formulated by English chemist Thomas Lowry (1874-1936) and Danish chemist J. N. Brønsted (1879-1947), Brønsted-Lowry theory defines an acid as a proton (H + ) donor, and a base as a proton acceptor.
The positively charged ion that results when an atom loses one or more electrons. "Cation" is pronounced "KAT-ie-un".
A generic term used for any substance studied in chemistry—whether it be an element, compound, mixture, atom, molecule, ion, and so forth.
An acid formed when a base accepts a proton (H + ).
CONJUGATE ACID-BASE PAIR:
The acid and base produced when an acid donates a single proton to a base. In the reaction that produces this pair, the acid and base switch identities. By donating aproton, the acid becomes a conjugate base, and by receiving the proton, the base becomes a conjugate acid.
A base formed when an acid releases a proton.
An atom or atoms that has lost or gained one or more electrons, and thus has a net electric charge. There are two types of ions: anions and cations.
A form of chemical bonding that results from attractions between ions with opposite electric charges.
A compound in which ions are present. Ionic compounds contain at least one metal and non metal joined by an ionic bond.
LEWIS ACID-BASE THEORY:
The third of three structural definitions of acids and bases. Formulated by American chemist Gilbert N. Lewis (1875-1946), Lewis theory defines an acid as the reactant that accepts an electron pair from another reactant in a chemical reaction, and a base as the reactant that donates an electron pair to another reactant.
A logarithmic scale for determining the acidity or alkalinity of a substance, from 0 (virtually pure acid) to 7(neutral) to 14 (virtually pure base).
A term describing scientific definitions based purely on experimental phenomena. These convey only part of the picture, however—primarily, the part a chemist can perceive either through measurement or through the senses, such as sight. A structural definition is therefore usually preferable to a phenomenological one.
A substance that interacts with another substance in a chemical reaction, resulting in the creation of a product.
Ionic compounds formed by the reaction between an acid and a base. In this reaction, one or more of the hydrogenions of an acid is replaced with another positive ion. In addition to producing salts, acid-base reactions produce water.
A homogeneous mixture in which one or more substances (thesolute) is dissolved in one or more other substances (the solvent)—for example, sugar dissolved in water.
A substance that dissolvesanother, called a solute, in a solution.
A term describing scientific definitions based on aspects of molecular structure and behavior rather than purely phenomenological data.