The Chemistry of Life Life depends on chemical reactions. It is thus important to understand a little chemistry in order to do biology. An element is any substance that contains just one type of atoms. Such isotopes are often used to follow biological reactions e.g. in medical diagnosis. A compound is a molecule made of at least two different atoms.
Bonds can be covalent or ionic.
Cl becomes Cl- when it gains one. These types of bonds are typically found in inorganic compounds. There are many important ions in the human body. Covalent reactions occur when atoms share electrons in o rder to fill an orbital. They are typically found in organic compounds.