* Fluorine (F): Fluorine is in Group 17 (also known as Group VIIA) of the periodic table, the halogens. Halogens have a strong tendency to gain one electron to achieve a stable octet (8 electrons) in their outer shell. This makes fluorine a highly electronegative element. Therefore, the most stable ion of fluorine is F⁻ (fluoride ion).
* Bromine (Br): Like fluorine, bromine is also a halogen. It also has a high electronegativity and readily gains one electron to achieve a stable octet. The most stable ion of bromine is Br⁻ (bromide ion).
