Chlorine is an element of atomic number 17 and atomic mass of 35.45 atomic mass units. It belongs to Group 17 of the periodic table and is thus a halogen. Halogens are a highly reactive group of elements that, in addition to chlorine, include fluorine, iodine, bromine and another element that does not occur in nature, astatine, but is produced by bombarding bismuth with alpha particles. Halogens are extremely reactive because they have an unpaired electron in their outermost electron shell. Thus so highly reactive, chlorine is usually not found in a pure form in nature, but is rather typically bound to other elements such as sodium, calcium, or potassium. In its pure form, chlorine exists as a diatomic molecule, meaning a molecule containing two of the same atoms. This form of chlorine is a yellow-green gas at room temperature. Chlorine gas is more dense than air, condenses to form a...