1. Naming Covalent Compounds
Unit 1 – Day 8
Naming Covalent Compounds

2. Covalent Compounds
Covalent bonds form when two non-metals share electrons.
When electrons are shared, there is no charge on elements.
Because of this we can NOT use the criss cross method, or roman numerals.
Instead, we use prefixes.

3. To name molecular compounds:
A prefix is used to indicate the number of each atom present.
Prefix Atoms Example
mono 1 carbon monoxide
di 2 carbon dioxide
tri 3 sulfur trioxide
tetra 4 carbon tetrafluoride
penta 5 phosphorus pentabromide
hexa 6 sulfur hexafluoride

4. Writing Formulas Step 1: Write the symbols of the elements.
Step 2: Write the subscript for the number of atoms represented by the prefix.
E.g. sulfur trioxide
E.g. diphosphorus pentasulfide

5. Which goes first?
With two non-metals, how do you decide which one goes first?
We need to look at a value called “electronegativity” on the periodic table.
Whichever element has the lowest electronegativity will go first.
Example: Circle the correct formula.
Cl2S or SCl2 - NH3 or H3N

6. Practice… Carbon dioxide Phosphorus trichloride Sulfur hexaiodide
Nitrogen monoxide

7. Writing Names
Step 1: Determine the appropriate prefix for each element.
Step 2: Write the prefix and the name of the elements. Change the ending of the second one to –ide.
E.g. N2O
E.g. BrI

8. Practice…
N2O4
CF4
SO2
P2O5

9. Diatomic Elements
Some elements are diatomic – they exist naturally as two atoms of the same element bonded together.
Hydrogen gas H2 Bromine Br2
Oxygen gas O2 Iodine I2
Nitrogen gas N2
Chlorine gas Cl2
Fluorine gas F2