This is element #17, Chlorine. Chlorine is located in the halogen group, therefore it is extremely reactive since it is only 1 electron away from a full outer shell. NOTE: I meant to write that 1 mol of Cl2 occupies 22.37L, not 24.27, I apologize for the error. It covalently bonds with itself to exist as Cl2. Chlorine gas is extremely toxic and irritating, it reacts with water to make HCl and HClO, both of which are corrosive acids. Chlorine is deadly in elemental form and was used as a chemical weapon in World War I. It is highly reactive with metals and causes them to rust rapidly. Combustible materials burn vigorously in chlorine. When bound is Na or Ca and O, it makes the life saving disinfectants bleach (NaClO) and pool chlorine (Ca(ClO)2). To safely work with chlorine, you will need either a fume hood or: A respirator with sealed goggles, gloves, a lab coat and a spray bottle filled with sodium bicarbonate solution (NaHCO3). Enjoy!