What is the difference between Valency and Valence Electrons?

Atoms of elements combine with each other to become electrically neutral, and to attain their stable state. A molecule gets formed when two or more than two atoms from the same element, or from different elements react and make bonds with each other. An atom of sodium reacts with an atom of chlorine to make something which makes our food much more tastier, salt. Similarly, when iron is left outside for a few days, it reacts with the oxygen and moisture present in the air to form rust. In chemistry, one of the most important thing which we have to keep in mind whenever we are trying to combine or react two or more atoms with each other is its valency. But often we get confused between the terms valency and valence electrons.

No need to worry about it now, as in this article, I will be covering both the topics in detail along with an example to make it simple for you.

Valence Electrons

As we know that there are four main shells in an atom i.e. K (1st and the inner most shell), L (2nd shell), M (3rd shell) and N (4th shell). In an atom, the electrons are distributed from the inner most shell, that is the “K” shell.

In an electrically neutral atom (which has equal number of protons and electrons) of oxygen, there are 8 electrons which are spread across all its energy levels/shells. The electronic configuration of oxygen is 2 and 6, which means that it has 2 electrons in the K shell and 6 electrons in the L shell (using the formula 2n^2). Valence electrons are basically all the electrons in the outermost shell of an atom i.e. the 6 electrons in the L or the outermost shell of oxygen.

Valency

Now we know that the electrons in the outermost shell of an atom are called valence electrons, but do you know that we can use this to calculate its valency?

Most of the atoms like to have 8 electrons in its outermost shell, but sometimes the number of electrons present in an atom is not enough so that the atom can complete an octet (8 electrons in the outer shell) and to satisfy the octet rule. In such cases, the atom either loses these electrons or gains more electrons.

If an atom has more than 4 valence electrons and less than 8, we can subtract the number of valence electrons it has with 8 to get its valency. And if an atom has less than or equal to 4 valence electrons, and more than 0, its valency will be the number of electrons it has in its outermost shell.

As oxygen has 6 valence electrons, it’s valency will be 8 -VE (valence electrons) or 8 - 6, that is 2. Sodium has only 1 electron, therefore its valency will be 1.

So therefore, we can say that Valency is the combining capacity of an atom.

That’s it!

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