Question

(15The successive ionization energies for element X is
given below
IE, : 250 kJ mol-1
IE : 820 kJ mot
IEZ : 1100 kJ mol-1
IE : 1400 kJ mol-1
Find out the number of valence electrons for the
element X​

Answer 1

explanation : before going to check out valency of element X . let's understand what is the meaning of ionisation energy ?

“ it is the amount of energy required to remove an electron from an isolated gaseous atom. ”

it is easy to understand, ionisation energy will be lower in value, when we remove an electron from an outermost shell (known as valence shell) which has unstable configuration.

if an element has successive ionisation energies are I.E1 , I.E2 , I.E3, ....

in such a way that,

I.E1 < (I.E2 - I.E1),

then, definitely valency of element is 1. [ because if we assume valency of element is 1 , then after removing an electron , made ion has stable configuration which has require lot of energy to remove another element. that's why (I.E2 - I.E1) > I.E1 ]

here same case is appearing.

I.E1 = 250 , (I.E2 - I.E1) = (820 - 250) = 570

i.e., (I.E2 - I.E1) > I.E1

so, valency of element is 1.

hence, number of valence electron for the element X is 1.