For 10 points, give the collective for these five elements of group 17, which includes the most electronegative element and others such as astatine, bromine and chlorine.
The heaviest one is extremely rare and is produced by bombardment of bismuth with helium. The lightest one forms a diatomic acid useful in etching glass. The least reactive is the second-heaviest one, a purple solid first isolated from seaweed. A silver salt of the third heaviest is used in photography, and the second lightest is abundant in seawater. For 10 points, give the collective for these five elements of group 17, which includes the most electronegative element and others such as astatine, bromine and chlorine.
The heaviest one is extremely rare and is produced by bombardment of bismuth with helium.
{halogens} [accept early {Group 17} or {Group 7A}]