The halogens are highly reactive elements residing in column 7A of the periodic table that commonly form ions with a -1 charge. They are recognizable by their -ine ending. They consist of fluorine, chlorine, bromine, iodine, and astatine. The four lightest halogens can all form stable hydrogen halides with hydrogen; three of these, hydrogen iodide, hydrogen bromide, and hydrogen chloride, are strong acids, though hydrogen fluoride is arguably the most dangerous. Halogens see extensive use in organic chemistry as well as inorganic, particularly in the case of fluorine and chlorine.