Let us take a look at the following atoms and find out the valence electrons present in them.
Table lists out atomic number, electronic configuration
and valence electrons of some atoms
| Element | Atomic Number | Electronic Configuration | Valence Electrons |
|---|---|---|---|
| Sodium | 11 | 2,8,1 | 1 |
| Carbon | 6 | 2,4 | 4 |
| Oxygen | 8 | 2,6 | 6 |
| Calcium | 20 | 2,8,8,2 | 2 |
Valence electrons help in bonding between atoms in two ways:
a) By transferring an electron or electrons from one atom to another. The type of bond is called the ionic bond.
b) By sharing of electrons between two or more atoms. This type of bond formed is known as the covalent bond.
The atoms involved in bonding attain a stable configuration. Noble gases like neon, argon, xenon, helium or radon have the stable electronic configuration.
When chemical bonds are formed, the atoms involved in bond formation attain the electronic configuration of noble gases. Study the electronic configurations of the following noble gases :
He - 2
Ne - 2,8
Ar - 2,8,8
All these elements except helium have eight electrons in the outermost shell. This is known as the octet configuration. This octet configuration is attained by most ions. Some atoms also attain the helium configuration. This is known as the duplet configuration.
Kossel and Lewis, in 1916, came to the conclusion that the noble gases have stable electronic configuration and hence they are inactive. They also stated that a duplet or an octet configuration of electrons in the valence shell is the most stable. Any atom with this configuration will be in the minimum state of energy, hence stable.
Atoms try to attain the octet or the duplet configuration by either loss or gain of electrons.
- Metal atoms tend to lose electrons.
- Non metal atoms tend to gain electrons.
Example:
Lithium has an atomic number of 3.
Electronic configuration = 2,1.
A lithium atom loses one electron to attain the duplet configuration of the helium atom.
