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

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

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.

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

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

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

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