For 10 points, identify this group of elements that lack one electron in their outer shell, examples of which are fluorine, chlorine, and bromine.
The 209 isotope of one member of this class of elements is produced by bombarding bismuth with alpha particles, while another of these elements is used as a mordant in Gram stains. Elements in this group are diatomic in their pure state, and this group has a name meaning salt-formers. Elements in this group can exist in solid, liquid, and gas phases, and the first element in this group is the most electronegative of all elements. For 10 points, identify this group of elements that lack one electron in their outer shell, examples of which are fluorine, chlorine, and bromine.
The 209 isotope of one member of this class of elements is produced by bombarding bismuth with alpha particles, while another of these elements is used as a mordant in Gram stains.
{halogens} [accept {group} 7A or {group 17}]