Question

it is easy yo calculate valency of elements. but how to calculate valency of compounds like nitrate or oxide? plz explain full procedure​

Answer 1

Valency is calculated for atoms... not compounds.

All atoms don't have octet configuration and thus, are not stable. So, they can't exist independently.

Compounds are stable as they are formed by satisfying the octet configuration of the constituent atoms.

Hope u understand.....

Answer 2

We never calculate the valency of the compounds, we calculate the valency of the atoms of an element present in a compound.

Now what is a valency first?

⇒ Valency is the gaining or losing capacity of electrons of an atom.

If an atom loses electrons then it forms positive ion or cation and similarly when an atom gains electrons then it forms negative ion or anion.

*The metals always form cation because it has 3 or less than 3 electrons in its valence shell so, its tendency is more to be stable by losing electrons. Similarly, a non-metal always forms anion because a non-metal has 5 or more than 5 electrons in its valence shell so, tendency of a non-metal is more to be stable by losing electrons.

*An ionic bond is always formed between a metal and a non-metal and a co-valent bond is always formed between two non-metals as they mutually shares their electrons and become stable so, there is no formation of charge.

Now, how to calculate the valency of an atom?

⇒ Let's explain it by the example of an ionic compound. Say about magnesiumoxide.

It is a compound of of magnesium(Mg) and oxygen(O).

In the last orbit of Mg has 2 electrons.

The last orbit of O has 6 electrons.

We get the compound as_

Mg²⁺ O²⁻

= Mg₂O₂

= MgO

∵ The elements of a compound are always expressed in the simplest ratio.

Here we see that, to become stable Mg loses 2 electrons so, as per the definition the valency of Mg is 2 and similarly to become stable O accepts 2 electrons and the valency of O is 2.

For your own identifying:

For a metal:

The number of electrons in the valence shell is the valency of the atom.

For a non-metal:

Subtract the number of electrons in the valence shell of the atom from 8 and the result is the valency of the atom.