Reactivity of Non-Metals
The elements of group 7 (7B) are the halogens, fluorine, chlorine, bromine and iodine, whose atoms have outer shells with one electron short of a full set. They react strongly with atoms with surplus electrons, to form negative ions. This activity decreases from fluorine to iodine. Atoms which need two electrons to complete their outer shells (oxygen, sulphur, selenium, tellurium and the radioactive metal polonium) are rather less active. Besides the inert gases, there are only 15 non-metals, of which some, arsenic and tellurium, are border-line cases and sometimes behave as metals.
Carbon, which forms strong covalent bonds with other carbon atoms, as well as with hydrogen, oxygen, sulphur, nitrogen, phosphorus and the halogens, is the cornerstone of organic chemistry. Single carbon-carbon bonds are less reactive than double bonds which, in turn, are less reactive than triple bonds, although six-membered aromatic rings with alternate single and
While some elements are much more reactive than others, their reactivity usually only manifests itself when one element is brought into contact with other elements and compounds. The greatest activity occurs when elements with opposite and complementary properties are brought together, e.g. caesium and fluorine. In the same way, compounds with opposite and complementary properties show the greatest activity when they mix, e.g. acids with bases and oxidising agents with reducing agents.