Class 9 Science

# Electronic Configuration

• Rules for electronic configuration
• Electronic configuration of H, He, Li, Be, B, C

Arrangement of electrons in different orbits is called electronic configuration. The maximum number of electrons can be obtained by 2n2 where n is the orbit number. Thus after knowing the maximum number of electrons for a particular shell, the arrangement of electrons in an atom can be identified. It is called Bohr Bury Schemes.

## Rules to write the electronic configuration of an atom

1. Maximum number of electrons in an orbit is calculated by 2n2, where n is number of orbit and may be equal to 1, 2, 3 , . . . .
2. Electrons occupy the next orbit only after filling the inner orbit completely.
3. The maximum number of electrons in outermost orbit will not be more than 8.

### Electronic configuration of Hydrogen

Atomic number of hydrogen = 1

Therefore number of electrons = 1

Maximum number of electrons in 1st orbit = 2

Since, hydrogen has only one electron, therefore, it will reside in 1st orbit.

Thus electronic configuration of hydrogen

Number of orbit present in hydrogen = 1

### Electronic configuration of Helium

Atomic number of helium = 2

Therefore number of electrons = 2

Therefore, electronic configuration of helium is

Number of orbit in helium atom = 1

### Electronic configuration of Lithium

Atomic number of Lithium = 3

Therefore number of electrons = 3

Since the maximum number of electrons in 1st orbit is equal to 2, therefore, after accommodating 2 electrons in 1st orbit, the third electron will go in 2nd orbit.

Thus, electronic configuration of lithium is

Number of orbit in Lithium atom = 3.

### Electronic configuration of Beryllium

Atomic number of beryllium = 4.

Therefore number of electrons = 4.

Thus, electronic configuration of Beryllium is

Number of orbit in beryllium = 2

### Electronic configuration of Boron

Atomic number of boron = 5

Therefore number of electrons = 5

Thus, electronic configuration of boron is

Number of orbit in boron = 2

### Electronic configuration of Carbon

Atomic number of carbon = 6

Therefore number of electrons = 6

Thus, electronic configuration of carbon is

Number of orbit in carbon = 2