it really helped me.. but i want to know that can we find valence electrons in elements with help of 2n^2 formula if yes then how?

Asked by vans75a | 2nd Jan, 2016, 07:46: PM

Expert Answer:

The maximum number of electrons present in the shell is given by theformula (2n2), where n is the orbit number or shell number.

 First orbit or K shell will be = 2 X 1= 2, Second orbit or L shell will be = 2 X 22 = 8,   Third orbit or M shell will be = 2 X 32 = 18, Fourth orbit or shell will be = 2 X 42 = 32 and so on.

Shell designation

Shell number

 (n)

Formula

2n2

Maximum number ofelectrons in each shell

K-shell

1

2 x (1)2

2

L-shell

2

2 x (2)2

8

M-shell

3

2 x (3)2

18

N-shell

4

2 x (4)2

32

 

The maximum number of electrons that can be accommodated in the outermost orbit is 8.

Further,

Starting with the energy level/shell closest to the nucleus electrons fill the different shells in order of increasing energy.

Shell 1 (K shell)

Shell 2 (L shell)

Shell 3 (M shell)

Shell 4 (N shell)

------------------------------- Increasing Energy ----------------------------->

Energy levels or shells can be divided into sub-shells, which can hold different numbers of electrons.

 

Shell 1 (K shell)

Shell 2 (L shell)

Shell 3 (M shell)

Shell 4 (N shell)

Sub-Shell

s

s

p

s

p

d

s

p

d

f

                     

Within each sub-shell there are one or more orbitals. Each orbital canhold a maximum of two electrons (of opposite spin).

 

Shell 1

Shell 2

Shell 3

Shell 4

Sub-Shell

s

s

p

s

p

d

s

p

d

f

Number of orbitalsin sub-shell

1

1

3

1

3

5

1

3

5

7

Number of electronsallowed in each orbital

2

2

2

2

2

2

2

2

2

2

Total number ofelectrons in each sub-shell

2

2

6

2

6

10

2

6

10

14

 

Atomic number of magnesium is 12; therefore electronic configuration will be 1s22s2 2p63s2. 

There are three shells, out of that third shell consist of two electrons.

 Hence 3s is the valance shell and electrons in this shell are valence electrons of Mg.

Similarly there are seven valence electrons in bromine (Br = 1s22s22p63s2 3p6 3d104s2 4p5).

Answered by Vaibhav Chavan | 3rd Jan, 2016, 01:18: PM

Queries asked on Sunday & after 7pm from Monday to Saturday will be answered after 12pm the next working day.