In GCSE Chemistry students must have a good knowledge of the periodic table. Most UK exam boards still follow the convention that the number of electrons in the outer shell = number of group. Since most schools teach to that convention, we use it in our quizzes. If you study chemistry to higher levels, you will find that this is no longer the case other than for groups 1 and 2.
In this quiz we look at the group 7 elements - the halogens.
Halogens is a combination of ancient Greek words that mean 'salt formers'. This refers to the fact that the group 7 elements will produce salts directly with metals. The combination of sodium and chlorine for example produces sodium chloride - common salt.
Naming the salts formed from the halogens is fairly straightforward: remove the ending -ine and replace it with the ending -ide. So if the halogen iodine reacts with the metal potassium, the salt formed will be potassium iodide.
On the periodic table, the halogens are the last but one group (vertical column), right next to the noble gases. The group number is 7 which indicates that halogen atoms contain seven electrons in the outer shell (energy level). In order to achieve stability and have the same structure as the nearest noble gas, these atoms gain a single electron (rather than losing seven electrons which would take much more energy).