A neutral atom of element has 2K, 8K and 5M electrons. Find out the following : (a) Atomic No. of the element (b) Total No. of s electrons (c) Total No. of p- electrons (d) No. of protons in the nucleus and (e) Valency of the element.

Explanation

The electronic configuration of the element with with 2K, 8L and 5M electrons will be
`1s^(2)2s^(2) 2p_(x)^(2) 2p_(y)^(2) 2p_(z)^(2) 3s^(2) 3p_(x)^(1) 3p_(y)^(1) 3p_(z)^(1)`
(a) Total no. of electrons `=2+8+5=15 :.` Atomic No. of the element `=15`
(b) Total no. of s-electrons `=2+2+2=6`
(c) Total no. of p-electron `=6+3=9`
(d) Since the atom is neutral, `:.` No. of protons = No. of electrons = Atomic No. `=15`
(e) Since the element has only three half-filled atomic orbitals, therefore, valency of the element `=3`.