How are the naming systems of ionic and molecular compounds different?

1 Answer
Jan 8, 2015

The naming of ionic compounds is dependent upon the type of ionic molecule formed from alkali metals, alkaline earth metals or transition metals.

Binary Metal to Non-Metal

When a metal and non-metal form an ionic molecule the metal will retain the element name and the non-metal will taken the suffix -ide.

#NaCl# = Sodium Chloride
#KBr# = Potassium Bromide
#CaI_2# = Calcium Iodide

For Transition Metals we are reminded that these elements can carry more than one charge and can be named with stock naming using roman numerals to indicate the ionic charge or common naming using the suffixes -ic and -ous. The -ic suffix is used for the greater charge and -ous for the lesser charge. Examples would include #Fe^+3# is ferric and #Fe^+2# is ferrous, #Sn^+4# is stannic and #Sn^+2# is stannous.

#Fe_2O_3# is ferric oxide or Iron III oxide
The iron ion is +3 to balance the -2 oxide ion

#FeO# is ferrous oxide or Iron II oxide
The iron ion is +2 to balance the -2 oxide ion

Molecular Compounds also known as covalent compounds involve bonds between two non-metals. These bonds are dependent upon the number of atoms sharing electrons and therefore are named using numeric prefixes to identify atom counts.

mono = 1
di = 2
tri = 3
tetra = 4 (tetris four block per piece)
penta = 5
hexa = 6
hepta = 7
octa = 8
nona = 9
deca = 10

The prefix mono is never used with the first element.
The suffix -ide is always added to the second element.

#NO_2# is nitrogen dioxide
#N_2O_5# is dinitrogen pentoxide
#SiCl_4# is silicon tetrachloride
#P_6F_8# is hexaphosphorus octafluoride