Question

An atom of an element has 4th shell as the valence shell . The difference between electrons present in L and M,K and N shells are 1 and 0 respectively. Find the atomic number of the element.

Answer 1

Dear Student,

K = 1^st shell
L = 2^nd shell
M = 3^rd shell
N = 4^th shell
​​​​​​electrons are fully filled till second shell, that means K shell contains 2 electron in the 1s atomic orbital and L shell contains 8 electrons with 2 electrons in 2s and 6 electrons in 2p atomic orbitals.
M - L = 1
M - 8 = 1
M = 9 which means, these 9 electrons will be arranged as 2 in 3s, 6 in 3p and 1 in 3d atomic orbital.
​​​​​and, K - N = 0, which is possible only when K shell contains 2 electrons in 4s atomic orbital
Therefore, electronic configuration of atom will be
1s²2s²2p⁶3s²3p⁶3d¹4s²
So, the atomic number will be 21 and the element will be Scandium.

Regards.