Unit 1 – Day 8

Naming Covalent Compounds

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.

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

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

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

Practice…

Carbon dioxide

Phosphorus trichloride

Sulfur hexaiodide

Nitrogen monoxide

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

Practice…

N2O4

CF4

SO2

P2O5

Diatomic ElementsSome elements are diatomic – they exist naturally as two atoms of the same element bonded together.

Hydrogen gas H2 BromineBr2

Oxygen gas O2 Iodine I2

Nitrogen gas N2

Chlorine gas Cl2

Fluorine gas F2