Formulas and Names for Covalent
Compounds
• Ionic compounds bond in predictable
proportions
• Formulae for covalent compounds are hard to
predict b/c 2 non-metals can often bond in
different proportions
• Eg. sulfur and fluorine combine to form:
SF4
OR
SF6
• We need a way to tell them apart
Naming Covalent Compounds
• We add Greek prefixes to indicate the number
of each element
Prefix
Number
Prefix
Number
mono-
1
hexa-
6
di-
2
hepta-
7
tri-
3
octa-
8
tetra-
4
nona-
9
penta-
5
deca-
10
Naming Covalent Compounds
• Write the less electronegative element first
with the correct prefix
• Write the second element, with the correct
prefix
• Change the ending of the second element to
“ide”, just like ionic compounds
• “mono-” is only used for the second element.
If the first element has one atom, just use the
element name
Examples
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CO
CO2
SCl2
SF4
SF6
N2O5
P2O3
P4O10
Formulas for Covalent Compounds
• Use the prefixes to find the number of each
atom present
• Eg. disilicon hexabromide
• Exceptions for covalent compounds
H2O = water
NH3 = ammonia
CH4 = methane
Formulas and Names for Binary Acids
• Binary Acids – contain H and one other
element
• Many are gases at room temperature
– Only when dissolved in H2O do they become acids
• Use the prefix “Hydro” + second element
name + suffix “ic”, followed by acid
• Eg. HCl(aq) = hydrochloric acid
Note: aq = aqueous
Read as “in water”
Examples of Binary Acids
• HF(aq)
• H2S(aq)
• HCN(aq)
Formulas and Names for Ternary Acids
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Ternary Acids contain oxyanions
Oxyanions – polyatomic anions with oxygen
Anions ending in “ate” change to “ic”
Anions ending in “ite” change to “ous”
Write “acid” after the anion name
When writing chemical formulas (aq) must be
written after the formula
Examples
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HNO3
H2SO4
HClO4
HClO3
HClO2
HClO
=
=
=
=
=
=
nitric acid
sulfuric acid
perchloric acid
chloric acid
chlorous acid
hypochlorous acid
Try These
• HNO2
• H3PO4
• H2CO3