Acid A compound that yields H+ ions in solution or a solution with the concentration of H+ exceeding OH-. Acid ionization constant The equilibrium constant describing the degree of dissociation of an acid. Actinides The row of elements below the periodic table, from thorium to lawrencium. Alkali Synonym for base. Alkali metals The column of elements from lithium to francium. Alkaline earths The column of elements from beryllium to radium. Alkane A hydrocarbon without a double bond, triple bond or ring structure. Alkene A hydrocarbon with one or more double bonds and no triple bond. Alkyne A hydrocarbon with one or more triple bonds. Alpha particle A cluster of 2 protons and 2 neutrons emitted from a nucleus in one type of radioactivity. Anion An atom or molecule with a negative charge. Anode The negative electrode at which oxidation occurs. Aqueous Refers to a solution with water as solvent. Aromatic Refers to an organic compound with a benzene-like ring. Atom The smallest amount of an element; a nucleus surrounded by electrons. Atomic number The number of protons in the nucleus of the chemical element. Atomic weight The weight in grams of one mole of the chemical element; approximately the number of protons and neutrons in the nucleus. Avogadro's Law Equal volumes of gases contain the same number of molecules. Avogadro's Number 6.02 x 1023 , the number of molecules in 1 mole of a substance.