Matter around us is made up of varieties of molecules. Atoms of different elements form these molecules. A force of attraction between the atoms holds them in the molecules. These forces of attraction that bind the atoms are called chemical bonds.
To attain stability the atoms need 8 electrons in their outermost shell for which they lose or gain electrons. Some atoms share electrons. This results in the formation of bonds. There are two main types of bonds. They are ionic/electrovalent bonds and covalent bonds
Formation of ions:
When an atom loses electrons to get 8 electrons it its outer most shell, it becomes positively charged ion called ‘cation’.
On the other hand when an atom gains electrons, it becomes a negatively charged ion called ‘anion’.
The electrostatic force of attraction between the cation and the anion produced by the transfer of electrons from one atom to the other is called i0nic or electrovalent bond. The compounds that contain such bonds are called ionic compounds.
Atoms with 1, 2 or 3 electrons in their outermost shell lose electrons to form cations
Atoms with 5, 6 or 7 electrons in their outermost shell gain electrons to form anions.
Metals form positively charged cations and nonmetals form negatively charged anions.
Alkali metals are highly reactive as they have just one electron in their outermost shell.
Halogens, which are also highly reactive, need just one electron to fill their outermost shell.
Ionic bonding are formed between metals and nonmetals.
The electronic configuration of sodium is 2, 8, and 1. Neutral sodium atom loses one electron to form positively charged sodium ion.
The electronic configuration of chlorine is 2, 8, and 7. Chlorine atom accepts one electron from sodium and become negatively charged chloride ion.
The two atoms are held closer with an electro static force of attraction resulting in the formation of sodium chloride molecule which is neutral.
The electronic configuration of Mg is 2, 8, 2. and it donates 2 elctrons to form 'Magnesium ion' with two positve charge. Mg++
The electronic configuration of chlorine is 2, 8, and 7. Two chlorine atoms accept one electron each from magnesium. Thus one magnesium atom is bonded to two chlorine atoms.
The following diagram shows the bond formation in MgCl2