The group 7 elements are also known as the halogens. They include fluorine, chlorine, bromine and iodine, which all have seven electrons in their outer shell.
In a displacement reaction, a less reactive element is displaced by a more reactive element.
The group 7 elements are placed in the vertical column second from right in the periodic table.
Chlorine, bromine and iodine are the three Group 7 elements you are likely to see at school. Fluorine is too reactive to keep or produce safely at school. Group 1 elements form salts when they react with metals, which is why they are called the halogens .
Properties & Uses
Group 7 elementPropertiesTypical use Chlorine Green gas Sterilising water Bromine Orange liquid Making pesticides and plastics Iodine Grey solid Sterilising wounds
Reactions with Group 1 Element
The group 7 elements react vigorously with group 1 elements such as sodium and potassium. In each case, a metal halide is formed (fluoride, chloride, bromide or iodide).
Group 1\7ChlorineBromineIodine Lithium Lithium chloride - LiCl Lithium bromide - LiBr Lithium iodide - LiI Sodium Sodium chloride - NaCl Sodium bromide - NaBr Sodium iodide - NaI Potassium Potassium chloride - KCl Potassium bromide - KBr Potassium iodide - KI
Displacement & Reactivity
If a reactive element comes into contact with the compound of a less reactive element a chemical reaction may take place. The less reactive element is removed from the compound and replaced by the more reactive element.
For example, if chlorine is added to a solution of potassium bromide, the bromine is replaced by the chlorine forming potassium chloride. Bromine is formed at the same time and can be detected by its colour.
Examples of Displacement Reactions
HalogenMetal halideThe most reactive halogenReaction Chlorine Sodium bromide Chlorine Chlorine + sodium bromide → sodium chloride + bromine Chlorine Sodium iodide Chlorine Chlorine + sodium iodide → sodium chloride + iodine Bromine Sodium chloride Chlorine No reaction Bromine Sodium iodide Bromine Bromine + sodium iodide → sodium bromide + iodine Iodine Sodium chloride Chlorine No reaction Iodine Sodium bromide Bromine No reaction