<u>Answer:</u>
Atoms tend to gain or lose of shares electron in order to get 8 electrons in the outer shell which is called as Octet Rule. “Octa” means 8.
All atoms except noble gases have less than 8 electrons in its outer shell.
These atoms are unstable.
To attain stability atoms either gains or losses or shares electron to get 8 electrons in its outer shell.
Noble gases having 8 electrons in the outer shell is inert and non reactive.
Atomic number = number of electrons = number of protons.
Atomic number of sodium is 11
So the atom contains 11 protons and 11 electrons
To find the number of neutrons we make use of the formula
Mass number - atomic number = number of neutrons
From the periodic table, we know mass number of sodium is 23
So number of neutron = 23 - 11 = 12.
When a sodium atom loses an electron it will have 11 positive protons and 10 negative electrons. Since 1 positive charge is more, Na becomes 
.
Positively charged ion is called as cation
Chlorine atomic number is 17 so it has 17 protons and 17 electrons.
When it gains an electrons it will have 17 positive protons and 18 negative electrons since 1 negative charge is more, Cl becomes 
.
Negatively charged ion is called as anion.
The electrostatic attraction between Na+ and Cl- due to the opposite charges gets attracted and forms a bond called ionic bond.
Covalent bond is the bond formed by sharing of electrons. Covalent bond is found among non metals.
For example
are some examples in which we can see covalant bonds
Two atoms of chlorine shares its electrons to form a covalent bond. Chlorine contains 7 electrons in its outer shell.
First chlorine shares its electron with the second one to make it get 8 electrons in its outer shell.
Same way second chlorine shares its electron with the second one to make it get 8 electrons in its outer shell
Each chlorine shares one of its electron with the other to make the other atom to get 8 electrons in the outer shell.
Oxygen contains 6 electrons in its outer shell. Each Oxygen atom shares two of its electron with the other oxygen atom to make it get 8 in the outer shell.
Having 8 electrons in the outer shell makes the atom stable. Thats why atoms either gains or loss or shares electrons to get 8 electrons in the outer shell.
