The maximum number of electrons can be obtained by 2n^{2}; 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

Maximum number of electrons in an orbit is calculated by 2n^{2}, where ‘n’ is number of orbit and may be equal to 1, 2, 3 , . . . .

Electrons occupy the next orbit only after filling the inner orbit completely.

The maximum number of electrons in outermost orbit will not be more than 8.

Chapter List

Electronic configuration of Hydrogen

Atomic number of hydrogen = 1

Therefore number of electrons = 1

Maximum number of electrons in 1^{st }orbit = 2

Since, hydrogen has only one electron, therefore, it will reside in 1^{st }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 1^{st }orbit is equal to 2, therefore, after accommodating 2 electrons in 1^{st }orbit, the third electron will go in 2^{nd} orbit.