Class 9 Chemistry Atoms and Molecules Valency

Valency

It is the ability of an atom to gain or lose electron in order to achieve the noble gas configuration. It refers to the ability of an element to combine with other element. It is obtained by determining the number of electrons in the outermost shell (also called valence shell) of each atom of an element. For instance, sodium has 1 electron in its outermost shell and hence valency of sodium is 1.

Fig. Atomic number of sodium is 11. So the electronic configuration stands out to be 2,8,1 i.e. there is one electron in the outermost shell. In order to gain inert gas configuration it is better for sodium to lose one electron and achieve the nearest noble gas configuration of neon with atomic number 10.

 On the other hand atomic number of chlorine is 17. So electronic configuration stands out to be 2,8,7. In order to achieve noble gas configuration to become stable it requires one electron then it will acquire the configuration of neon (noble gas). Therefore valency of chlorine is1.

That means the every element tries attain stability by acquiring noble gas configuration for which it tries to either gain electron or donate electron. Na donates 1 electron in its outermost shell to attain noble gas configuration whereas chlorine acquires 1 electron in its outermost shell to acquire noble gas configuration.

Metals are electropositive because they have tendency to lose electrons. E.g. Na+ whereas non-metals are electronegative since they have a tendency to gain electrons. E.g. Cl-.

We can find the valency of an element through its atomic number and its electronic configuration. For instance,

  • In Boron with atomic number 5, the configuration stands out to be 2,3 and it has 3 electrons in its outermost shell. Being a metal Boron has a tendency to lose its electrons to gain noble gas configuration and shows its valency 3.
  • Whereas in Fluorine with atomic number 9, the configuration stands out to be 2,7 and it has 7 electrons in its valence shell and needs to gain 1 more electron to achieve noble gas configuration and hence its valency is 1.

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