9th science

# Structure of The Atom

## Arrangement of electrons in an atom – Electronic Configuration

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.

## 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.

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

Thomson Model

Bohr Model

Atomic Number

Electronic Configuration

Elec Config N to Mg

Elec Config Al to Ca

Valency

In Text Solution

NCERT Solution