1. 1.3 Molecular Elements Diatomic Elements
LO: I understand the bonding forces that exist in diatomic elements.

2. A covalent bond holds the two atoms in a diatomic molecule together, e
A covalent bond holds the two atoms in a diatomic molecule together, e.g. fluorine:
F — F
This bond is an bond
(intra = inside)
covalent bond
intramolecular
Fluorine also has weak forces holding the molecules together.
van der Waals
These forces are
forces.
(inter = between)
F — F
intermolecular
van der Waals forces
It is the forces that are responsible for physical properties like melting and boiling points.
intermolecular

3. Melting point trend in the halogens:
(˚C)
Period Number F2
Cl2
Br2 I2
At2
increases
The melting point of the halogens down the group.
This is because the van der Waals forces are increasing with increasing
atomic size
energy
More is needed to break these forces so the melting point increases.

4. Larger Covalent Molecules
LO: I understand how the intermolecular forces are affected by the size of molecules.

5. However, the number of in each molecule is not equal.
35.5
31.0
32.1
The atoms in these elements are of size and so the van der Waals attractions between them will be
similar
similar
atoms
However, the number of in each molecule is not equal.
number of atoms
The greater the in a molecule, the greater the number of between each molecule.
van der Waals
As the number of van der Waals attractions between the molecules increases, the melting point
increases

6. Molecular Carbon
LO: I know about the molecular form of carbon.

7. Molecular forms of carbon have been discovered with or more atoms per molecule.60
These carbon molecules are called
fullerenes
They are joined together to make spheres which have a low density due to the in the centre.
empty space
Fullerenes have a moderately high melting point due to the large number of between the molecules.
van der Waals forces