Ionic bonds, as you can probably surmise form from ions. Ions are made when an atom gains an electron to form a negative ion or loses an electron to form a positively charged ion. As an example of an ionic bond let's used the elements Cl and Na. First, we must understand that there is an attraction between them because one is positive and the other negative and that the Cl atom contains seven valence electrons and Na one. So, as the atoms bond the Na loses its valence electron and Cl gains it making its outer shell complete and it more stable. During this reaction light and heat are given off. This shows an exothermic reaction, which is a release of energy. The electrostatic energy between the two holds them together. Ionic bonds are useful because in a liquid state it can conduct electricity. This is possible because it contains ions. That doesn't conduct electricity in the solid state because there is not enough room within the molecule. The substance produced by this bond is table salt. Other salts, such as CaCl (rock salt) are formed in the same way and although they have a different crystalline structure they do possess the same physical properties.
Covalent bonds, as stated earlier, are when the atoms share electrons with each other. Covalent bonds can exist in each of the phases of matter. As a covalent bond is formed energy is released, sometimes violently as in the case of