1. Covalent bonding:
When two non-metal atoms join to one another they tend not to form ions. Why do you think this is?
Clue: What happens to non-metals when they form ions?

2. Covalent bonding:
Instead of losing and gaining electrons, the non-metal atoms share electrons.

3. Covalent bonding:
Definition: A covalent bond is a shared pair of electrons

4. Covalent Bonding Cl Cl
How many electrons are there in the outer shell of and atom of 17Cl?
If two atoms of chlorine form one covalent bond, each of the atoms would then have eight electrons in its outer shell.

5. If an atom needs to share more than one electron to obtain a Nobel gas configuration, it can form more than one covalent bond.
These bonds could be between the same two atoms, giving rise to double or triple bonds
Or they could be between several atoms
For GCSE purposes you can assume that each atom involved in a covalent bond provides one electron. O O H C H H H

6. A molecule is two or more atoms joined by covalent bonds.
Molecules
The word “molecule” is one which is often misused. What does it mean?
Definition:
A molecule is two or more atoms joined by covalent bonds.

7. Draw dot and cross diagrams for the following molecules
Draw dot and cross diagrams for the following molecules. Show outer shell electrons only.
Bromine (Br2)
Hydrogen (H2)
Nitrogen (N2)
Water
(clue: put the oxygen in the middle)
Carbon dioxide
(clue: put the carbon in the middle)

8. Top tips for covalent dot and cross diagrams:
Work out number of outer shell electrons
Work out the number of covalent bonds needed to get a noble gas configuration.
Draw those covalent bonds
Fill in any left-over electrons in the outer shells not involved in bonding.

9. Simple covalent molecules
Most molecules are made of a finite number of atoms.
For example H2, NH3, or C10H22
These are described as simple molecules.

10. Examples of simple covalent moleculesCl Cl H C H H
Chlorine (Cl2) H O O
Methane (CH4)
Oxygen (O2)

11. Simple covalent molecules
The bonds within the molecules are covalent.
The bonds between the molecules are much weaker bonds often referred to as intermolecular bonds.
Because these intermolecular bonds are weak, simple covalent substances will have low melting and boiling points.

12. Giant covalent molecules
Some molecules are very large and, in theory, could contain any number of atoms.
These are called giant molecules.

13. Examples of giant covalent molecules
Diamond
Graphite

14. Molecules are very large and could contain any number of atoms.
Sort the following properties into the table below:
Molecules are very large and could contain any number of atoms.
All the atoms are interconnected by strong covalent bonds
Bonds between the molecules are much weaker bonds often referred to as intermolecular bonds.
Have high melting points and boiling points.
Have low melting and boiling points.
Properties of simple covalent structures
Properties of giant covalent structures
Finite number of atoms

15. Properties of giant covalent molecules:
In giant covalent molecules all the atoms are interconnected by strong covalent bonds.
This means that giant covalent structures will generally have very high boiling points (also known as fixed points)

16. Conductivity of giant covalent molecules
Most giant covalent structures do not have charged particles which are free to move.
Therefore most giant covalent substances will not conduct electricity.
One exception to this rule that you should know is graphite.

17. Conductivity of graphite
Graphite consists of layers of covalently bonded carbon atoms, resembling a honeycomb structure
Between these layers are delocalised (free) electrons.
These electrons are free to move through the graphite.
Therefore graphite can conduct electricity.
Electrical current

18. Graphite is also slippery
The covalent bonds between the carbon atoms in graphite are very strong, giving it a high melting point. However, between the layers of graphite there are weak intermolecular forces. These intermolecular forces can break and reform relatively easily allowing the layers to slide over one another. This makes graphite soft and slippery.

19. 6 Mark Question
Explain how you would prove whether a compound is ionic rather than giant covalent or simple molecular. You may use diagrams in your answer.

20. 6 Mark Question – Mark Scheme
SM will have low boiling point
SM was be a gas at room temp
GC and Ionic will have high boiling points
GC insoluble in water (or reverse)
GC and Ionic will not conduct electricity when solid
Ionic will conduct electricity with molten or in solution
Graphite conducts electricity