Some preventive steps, including bathing after exposure, may reduce symptoms. Chlorine is an element added to pools and hot tubs to help disinfect water, making it safer to swim in. It’s also ...

There are only seven diatomic elements that default to this double bond. Five of them — hydrogen, nitrogen, fluorine, oxygen and chlorine — are gases at room temperature and normal pressure.

We also, confusingly, tend to refer to pure substances made of one kind of atom, like chlorine gas, as elements. But these are very different from the isolated atoms depicted on the periodic table.