Chemistry Unit 2 AS

Group 7, the halogens

- Physical properties, fluorine is a pale yellow gas, chlorine a greenish gas, bromine a red-brown liquid and iodine a black solid

o Fluorine is small and leads to the repulsion between non-bonding electrons because they are so close together

o The atoms get bigger as we go down the group because each element has one extra filled main level of electrons compared with the one above it

|Halogen |Atomic number |Electron Arrangement |Electronegativity |Atomic radius nm |Melting point K |Boiling Point K |
|Fluorine |9 |[He]2s22p5 |4.0 |0.071 |53 |85 |
|Bromine |35 |[Ar]3d104s24p5 |2.8 |0.114 |266 |332 |

Electronegativity

- This is a measure of the ability of an atom to attract electrons, or electron density towards itself within a covalent bond

o This depends on the attraction between the nucleus and bonding electrons in the outer shell, which depends on the balance between the nuclear charge and the distance between the nucleus and the bonding pairs plus the shielding effect of inner shells of electrons

Melting and boiling points

- Melting and boiling points involve weakening and breaking van der Waals forces only, the covalent bonds in the halogen molecules stay intact

o The lower the boiling point the more volatile the element

Chemical reactions of the halogens

- The oxidising ability of the halogens increases as we go up the group

Displacement reactions

- Halogens will react with metal halides in solution in such a way that the halide in