When a non-metal element reacts with a non-metal element, a covalent bond is formed
Covalent bonds
They are strong - a lot of energy is needed to break them
Substances with covalent bonds often form molecules with low melting and boiling points
There are strong covalent bonds within the molecules (between the atoms), but weak intermolecular forces between the molecules
Formation of a covalent bond
1. Two non-metal atoms share a pair of electrons in their outer shells
2. The electrons involved are in the outer shells of the atoms
3. An atom that shares one or more of its electrons will complete its outer shell
Molecule
A collection of two or more atoms held together by chemical bonds
Covalent bonds are strong - a lot of energy is needed to break them
Substances with covalent bonds often form molecules with low melting and boiling points
There are strong covalent bonds within the molecules (between the atoms), but weak intermolecular forces between the molecules
Only a small amount of heat energy is required to separate the molecules from each other
Stable
Atoms are stable if their outer shell contains its maximum number of electrons
Both nuclei are strongly attracted to the shared pair of electrons in the covalent bond, so covalent bonds are very strong and require a lot of energy to break
Multiple covalent bonds
Atoms may form not only one pair of shared electrons, but two or more pairs
Number of covalent bonds an element will form
1
2
3
4
Rule for number of covalent bonds
Number of covalent bonds = 8 - group number
Hydrogen forms one covalent bond
The noble gases in Group 0 do not form any covalent bonds
