MOLECULAR COMPOUNDS

Science 10

What is a molecular compound?

A substance made up of molecules that is only composed of nonmetals

They are different from ionic compounds because those are made up of a metal and nonmetal

Electrons are shared between nonmetals to form a covalent bond

The simplest molecules are diatomic (composed of two nonmetals) Ex. Cl2

Other molecules are composed of different nonmetals Ex. C6H12O6, H2O

How to Write the Formula of a Molecular Compound

The number of electrons that a nonmetal can share is called its combining capacity

When predicting the formula of a molecule, use the combining capacity (group number) of the nonmetal

Ex. C = group 14 (loss of 4 e-), O = group 16 (gain of 2e-)C4O2

C2O4

These formulas are not reduced

Combining Capacities of Nonmetals

4 3 2 1

H

C N O F

Si P S Cl

As Se Br

I

Naming Molecular Compounds

Instead of using the ionic compound naming rules, we use the prefix system to name molecules

Prefix Number Example

mono- 1 carbon monoxide (CO)

di- 2 carbon dioxide (CO2)

tri- 3 carbon trioxide (CO3)

tetra- 4 carbon tetrafluoride (CF4)

penta- 5 phosphorous pentafluoride (PF5)

Some Rules to Remember

If there is not a subscript on the first nonmetal, the prefix mono does not have to be used

If there are subscripts on both nonmetals, use prefixes for both

Use the common name for the compound when applicable Ex. H2O is dihydrogen monoxide but you can call it

water