ORBITALS

Structure of atom of Class 9

ORBITALS

Like shells are divided into subshells, subshells further contain orbitals.

An orbital may be defined as a

“Region in the three - dimensional space around the nucleus where the probability of finding an electron is maximum. The maximum capacity of each orbital is that of two electrons.”

Sub shell 

Orbital (s)

Max. no. of electrons 

s

1

2

p

3

6

d

5

10

f

7

14

  The total number of nucleons is equal to the mass number (A) of the atom.

BOHR-BURY SCHEME OF DISTRIBUTION OF ELECTRONS:

The following rules are given by Bohr and Bury for writing the number of electrons in different energy levels or shells:

(i) The maximum number of electrons that can be present in a given shell is equal to 2n2, where n = number of shell.

Hence, the maximum number of electrons in different shells can be given as follows: 

Shell

Maximum No. of electrons present

(a) 1st shell or K-shell (n = 1)

2 × (1)2 = 2

(b) 2nd shell or L-shell (n = 2)

2 × (2)2 = 8

(c) 3rd shell or M-shell (n = 3) 

2 × (3)2 = 18

(d) 4th shell or N-shell (n = 4)

2 × (4)2 = 32

  •  The maximum number of electrons that can be accommodated in the outermost orbit is 8.
  • Electrons do not enter into a new shell until and unless the inner shells are completely filled or we can say that shells are filled in a step-wise manner.

Element

Symbol

Atomic No. (No. of electrons)

Distribution of electrons in different shells

Short representation of electronic configuration

K

L

M

N

Hydrogen

Helium

Lithium

Beryllium

Boron

Carbon

Nitrogen

Oxygen

Fluorine

Neon

Sodium

Magnesium

Aluminium

Silicon

Phosphorus

Sulphur

Chlorine

Argon

Potassium

Calcium

H

He

Li

Be

B

C

N

O

F

Ne

Na

Mg

Al

Si

P

S

Cl

Ar

K

Ca

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

1

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

1

2

3

4

5

6

7

8

8

8

8

8

8

8

8

8

8

8

1

2

3

4

5

6

7

8

8

8

1

2

1

2

2, 1

2, 2

2, 3

2, 4

2, 5

2, 6

2, 7

2, 8

2, 8, 1

2, 8, 2

2, 8, 3

2, 8, 4

2, 8, 5

2, 8, 6

2, 8, 7

2, 8, 8

2, 8, 8, 1

2, 8, 8, 2

Diagrammatically, the nuclear structure and the distribution of electrons can be represented as below:

ORBITALS

Schematic atomic structure of the first eighteen elements

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