Question

Define valency by taking examples of silicon and oxygen.

Answer 1

The number of electrons in the valence shell i.e. in the last shell of an atom is referred to as valence electrons. Valency is the number of electrons needed by the element to gain a stable configuration.

Complete Solution :
Firstly, let’s define valency and then we will discuss the examples.

- In chemistry, valency is the combining power of an element with other elements which leads to the formation of chemical compounds or molecules. We determine the affinity or the combining power of an atom by the number of hydrogen atoms (not necessarily hydrogen, it can be other atoms too) it combines with. For example, valency of oxygen in a water molecule is 2 as it combines with two hydrogen atoms.
- The electrons present in the outermost shell of an atom are known as valence electrons and they determine the valency. The valence electrons take part in a chemical reaction and they determine the chemical properties of the elements.
We should remember that, if the number of valence electrons of the atom of an element is less than or equal to four, then the valency of that element is equivalent to the number of valence electrons.
- On the other hand, when the number of valence electrons of the atom of an element is more than four, then the valency of that element is acquired by subtracting the number of valence electrons from eight.

- Now, let’s take an example of silicon and oxygen.
We know that the atomic number of silicon is 14. We can write its electronic configuration as 2, 8, 4. Now, to gain stable configuration i.e. 2, 8, 8 it needs 4 electrons. So, the valency of silicon is 4.
- Secondly, we have oxygen. We know the atomic number of oxygen is 8. So, we can write its electronic configuration as 2, 6. To gain stable configuration i.e. 2, 8 it needs 2 more electrons. So, its valency is 2.

Note: We often think that valency and oxidation number is the same thing but it is not. We should remember that oxidation number gives us the number of electrons the atom or molecule has gained or lost and we have already discussed valency in the above discussion.