Unlike covalent molecules, which consist of a small number of atoms, ionic compounds consist of large ions. They form as a result of the transfer of electrons between metal atoms and non-metal atoms. The process results in the formation of positively charged ions (cations) and negatively charged ions (anion). Ionic bonds are formed as a result of the metal atom losing electrons to form the cation and the non-metal atom gaining electrons to form the anion.
Compounds are usually named with the cation first and the anion second. However, some metals can form more than one ion. For these, a Roman numeral is added in parentheses after the metal name to show the number of ions present. For example, iron forms two ions with chlorine and is thus given the name iron(II) chloride.
Oxoanions often have suffixes, and sometimes prefixes, attached to their root to indicate the number of oxygen atoms present. For example, copper(II) sulfite has the formula CuSO45H2O. Similarly, calcium oxide has the formula CaO. Hydrates have a numerical prefix to indicate the number of water molecules. For example, barium hydroxide octahydrate has the formula Ba(C2H3O2)2.
Finding the molar mass of a compound is done by adding up the weights in kilograms per mole of all the atoms found in the formula. This is also called the formula weight. It is an essential step in calculating chemical equations, pressure and other types of compound properties. The molar mass of cesium sulfur is 0.998 g/mol.