Gourary and Adrian 1 have derived a set of new ionic radii for the alkali metal and halide ions using the experimental radii of sodium (1.17 Å) and chloride (1.64 Å) ions 2 as standard.

The word ‘halogen’ means 'salt former'. Group 0 and testing ions Flame tests identify alkali metal ions in compounds. The noble gases are very unreactive.