2. Purpose
• One needs to be able to correctly name a covalent substance
and determine a formula from a name.
3. Naming Covalent Compounds
• Naming covalent compounds is fairly straight forward
– First
• Name of the first atom with prefix indicating the number of atoms
– Second
• Name of the second atom ending in –ide with a prefix indicating the
number of atoms
[prefix] atom name [prefix] atom name ending in –ide
– Example:
• N2O5
– contains two nitrogen – dinitrogen
– contains five oxygens – pentoxide
– Together: dinitrogen pentoxide
4. Covalent Prefixes – Memorize Them
• The prefixes to use with the atom names are:
Number of atoms Prefix
1 mono-
2 di-
3 tri-
4 tetra-
5 penta-
6 hexa-
7 hept-
8 octa-
9 nona-
10 deca-
5. An important exception
• The one case where you do not use a prefix when naming a covalent
compound is when there is only one of the first atom in the formula. In
other words, if it will begin with mono-, you leave the mono- prefix off.
– Example:
• NO – nitrogen monoxide
6. Pause and practice
• Name the following:
– H2O
– P4O10
– SO2
• Give the formulas of the following:
– Dinitrogen monoxide
– Boron trihydride
– Silicon tetrachloride
7. Pause and practice Answers
• Name the following:
– H2O
• dihydrogen monoxide
– P4O10
• tetraphosphorus decoxide
– SO2
• sulfur dioxide
• Give the formulas of the following:
– Dinitrogen monoxide
• N2O
– Boron trihydride
• BH3
– Silicon tetrachloride
• SiCl4
