The atom is the smallest particle or fragment of an element that still retains its properties. It consists of a nucleus (made up of protons and neutrons) surrounded by electrons. Atoms combine with each other through chemical bonding to form molecules. Molecules are generally considered to be the smallest fragment that retains the properties of a chemical compound. Thus, atoms make molecules, molecules do not make atoms. A molecule is generally stable on its own, while an atom can be unstable depending on its electronic configuration. Unless the atom achieves the noble gas configuration, it can lose or gain electron (depending on its electronegativity) to achieve stability. Molecules can be made up of more than one atom, for example oxygen atoms can combine to form an oxygen molecule (O2), they can also combine with hydrogen to form a water molecule (H2O).