Covalent Compounds

Covalent compounds are formed when two or more atoms, usually nonmetal atoms, share electrons more or less equally.  The names of some covalent compounds were so well-known before the standard IUPAC naming systems were developed and are still referred to by their "common" names, for example, water ( H₂O) and ammonia (NH₃).  However, for most covalent  inorganic compounds, a few simple rules can be used to consistently name molecules.
 
 

Naming Covalent Compounds

 

• The element with the lower group number in the periodic table is named first.

• The element with the higher group number is second, except when the compound contains oxygen and a halogen -- halogen goes first.

• If both elements are in the same group, the one with the higher period number is named first.

• The second element is named with its root and the suffix "ide".

• The number of atoms in a molecule is signaled in the name by the use of Greek mumerical prefixes. For example, N₂O₄ is dinitrogen tetroxide >but NO₂ would be nitrogen dioxide.

Formulas for Covalent Compounds Since covalent compounds involve only neutral atoms, there is no need to balance the charge.  The order of the elements follows the same rules as the order for naming the moledules.     For example: Dichlorine heptoxide is Cl2O6 an exception to the rule that the element with the higher group number comes second since chlorine is a halogen. Bromine trichloride is BrCl3 because both bromine and chlorine are halogens but bromie is has the higher group number and so comes first.