MAGNESIUM OXIDE, Magnesium oxide is also an ionic compound, In the formation of this ionic compound magnesium loses two electrons successively, COVALENT BONDING

MAGNESIUM OXIDE:

             Magnesium oxide is also an ionic compound. In the formation of this ionic compound magnesium loses two electrons successively.

                         Mg                               e^- + Mg⁺

                        Mg⁺                             e^- + Mg2⁺

            Where as oxygen after gaining two electrons become oxide ion.

                         O + e^-                           O^-

                        O^- + e^-                          O^2-

2+

Mg

2-

O

            After the formation of ions, the oppositely charged attract each other and from a stable crystal lattice. The shape of this lattice is also face centred cubic but its cube is mole compact and have strong electrostatic forces of attraction as are present in the crystal lattice of sodium chloride. This is because magnesium ion and oxide have more charge on them as completed to sodium ion and chloride ion. Mostly melting point and boiling point of ionic compounds increases as the charge on ions increases. Hence sodium chloride with its uni-charged ions has a melting point of 801 ⁰C and magnesium oxide with it di-charged ions has a melting point of 2852 ⁰C. The dot-and-cross diagram of magnesium oxide is;

COVALENT BONDING:

             The chemical bond which is formed due sharing of electrons between adjacent atoms is called covalent of electrons between adjacent atoms is called covalent bond. Mostly due to mutual sharing each atom going to fill its outer most shell and tends to attain noble gas electronic configuration.

             If there is one shared pair of electrons i.e; one electron contributed by each atom then it is called single covalent bond and is represented by one short line (-) between two bonded atoms. Similarly if covalent bond is due to mutual sharing of two pairs of electrons i.e; two electrons by each atom then it is called double covalent bond and is represented by two short lines (=) between covalently bonded atoms and if covalent bond is formed due to mutual sharing of three electrons by each atom i.e; three shared pair between two adjacent atoms; then it is called triple  covalent bond and is represented by three short lines (  between two bonded atoms. A covalent bond may be represented by a dot-and-cross diagram. Each dot and cross represents an electron in the valence shell of an atom. 

 Another important fact that covalently bonded compounds are different from ionic compounds. They are mostly liquid, gases or solids with low melting points because group of covalently bonded atoms may exist separately hence they are called molecules. No doubt some covalent compounds also exist as gaint covalent crystalline lattice but they are very few e.g; Diamond, graphite,  Quartz crystals, solid iodine crystals etc.