ICSE Class 6 Answered

How to find valency of element? Also why there are negative and positive valent elements?

Asked by nandhithaaumbarish | 10 Nov, 2022, 04:40: PM

Expert Answer

Dear Student,

Importance of Valency:

Valency of any element is the number of electrons it has to lose or gain in order to become stable.

Reason for negative and positive valence elements:

If the atom has to lose electrons to become stable, then the valency will be positive and if the atom has to gain electrons to become stable, then the valency will be negative.

For example:

Sodium (Na) = E.C. = [Ne]3s¹

Sodium tries to donate one outermost valence shell i.e. 3s orbital to achieve nearest stable noble gas configuration i.e. of neon. Here, by donating nuclear charge of sodium remains same due to same number of protons but, due to loss of 1 electron having 1 negative charge, the overall charge on sodium ion after loss of 1 electron is +1 and represented as Na⁺¹

Thus, valency of alkali and alkaline earth metals is always positive.

In case of halogens such as chlorine,

Chlorine (Cl) = E.C= [Ne]3s² 3p⁵

Clorine by accepting 1 electron in outermost valence 3p shell, tries to achieve, closest inert gas configuration i.e. argon.

Here also, nuclear charge of chlorine remains same but, due to acceptance of 1 extra electron carrying 1 negative charge, chlorine ion fomred has −1 charge and represented as Cl⁻¹.

Thus, all halogens show negative valency.

Thanks and Regards

Answered by | 11 Nov, 2022, 12:16: PM