2.4 group 7 - the halogens

The elements that are found in group 7 of the periodic table

A group of toxic non-metals that have coloured vapours

• low melting and boiling points • poor conductors of heat and electricity

Increase

As molecules made up of pairs of atoms, called diatomic molecules. The atoms in each pair are joined to each other by a covalent bond

They gain one electron to achieve the stable electronic structure of a noble gas

They gain an extra electron by sharing a pair of electrons with another atom

Less

They gain a single electron to five them a stable arrangement of electrons and form ions with a 1- charge (ionic compounds)

Using the following rule: A more reactive halogen will displace a less reactive halogen from solutions of its salts

• the number of electron shells increases • halogen atoms from negative ions when they gain an electron to obtain a full outer shell • increased distance between the nucleus and the outermost shell electron mean s the forces of attraction decrease going down the group • this makes it harder for atoms to gain electrons going down the group

when a more reactive hydrogen displaces a less reactive hydrogen from a solution of its halide

• the solution becomes orange as bromine is formed or brown as iodine is formed • because chlorine is above bromine and iodine in group 7 so it is more reactive • chlorine will displace bromine or iodine from an aqueous solution of the metal halide

chlorine + potassium bromide –> potassium chloride + bromine Cl2 + 2KBr → 2KCl + Br2

chlorine + potassium iodide → potassium chloride + iodine Cl2 + 2KI → 2KCl + I2

• bromine is above iodine in group 7 so it is more reactive • bromine will displace iodine in an aqueous solution of the metal iodide

bromine + potassium iodide → potassium bromide + iodine Br2 + 2KI → 2KBr + I2