Define halogens.
Group 7 - The halogens The Group 7 elements are called the halogens. All the halogens' atoms 'go round in pairs'. They form diatomic molecules. In other words, ' two-atom' molecules , like F 2 and Cl 2 . Chlor ine changes to chlori de in its compounds. In general the halogens form halides . The halogens get less reactive going down the group.