## Friday, 5 January 2018

### Summarise the rules for writing of distribution of electrons in various shells for the first eighteen elements.

Answer : The following rules are followed for writing the distribution of electrons in different energy
levels or shells for the first eighteen elements :
(i) The maximum number of electrons present in a shell is given by the formula 2n2, where 'n' is the orbit
number or energy level index, 1,2,3,….Hence the maximum number of electrons in different shells are as
follows:
first orbit or K-shell will be = 2 × 12 = 2,
second orbit or L-shell will be = 2 × 2= 8,
third orbit or M-shell will be = 2 × 32= 18,
fourth orbit or N-shell will be = 2 × 42= 32,
(ii) The maximum number of electrons that can be accommodated in the outermost orbit is 8.
(iii) Electrons are not accommodated in a given shell, unless the inner shells are filled. That is, the shells are filled in a step-wise manner.

Distribution of electrons in various shells for the first eighteen elements
ElementSymbolAtomic NumberNumber of Electron
Distribution of electrons
 K L M N
Hydrogen
Helium
Lithium
Beryllium
Boron
Carbon
Nitrogen
Oxygen
Fluorine
Neon
Sodium
Magnesium
Aluminium
Silicon
Phosphorus
Sulphur
Chlorine
Argon
H
He
Li
Be
B
C
N
O
F
Ne
Na
Mg
Al
Si
P
S
Cl
A
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
 1 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 - - - - - - - - - - 1 2 3 4 5 6 7 8 - - - - - - - - - - - - - - - - - -