Ionic bonds occur between a metal and a nonmetal, where one atom donates an electron to the other atom. In this case, lithium (Li) is a metal and chlorine (C) is a nonmetal, resulting in the formation of an ionic bond. Covalent bonds occur between two nonmetals, where the atoms share electrons. Nitrogen (N) and oxygen (O) are both nonmetals, so they form a covalent bond by sharing electrons. Metallic bonds occur between metals, where the atoms share a 'sea' of electrons, which is the case with gold (Au) bonding with itself.