How to find the valency of a given element?

CBSE Class 9
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How to find the valency of a given element?

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Valency

  • Valency of an element represents the combining capacity of the element.
  • Valency of an element can also be defined as the number of electrons lost, gained or shared by its atom during chemical combination.

Valence shell
The outermost shell or orbit of an atom is known as valence shell or valence orbit.

Valence electrons

  • The electrons present in the outermost valence shell of an atom are called valence electrons.
  • The number of valence electrons varies from 1 to 8 for the atoms of the different elements.
  • The valence electrons of an atom determine the valency of that element.

If the atom has less than 4 electrons in its outermost shell then the atom will loose them and will gain plus (+) charge and will become positively charged ion called cation.

  • If 1 electron is lost then +1 charge
  • If 2 electrons are lost then+2 charge
  • If 3 electrons are lost then +3 charge

For example,

Sodium with atomic number 11 and electronic configuration 2, 8, 1 has one electron in its outermost shell. It will loose this electron to acheive stable electronic configuration of nearest noble gas and will become positively charged cation Na+.

If the atom has more than 4 electrons in its outermost shell then the atom will gain electrons and to acheive inert gas configuration and will become negatively charged anion.

  • If 1 electron is gained then -1 charge
  • If 2 electrons are gained then -2 charge
  • If 3 electrons are gained then -3 charge

For example,

Chlorine with atomic number 17 and electronic configuration 2, 8, 7 has seven electrons in its outermost shell. It will gain one more electron from the other atom to acheive stable electronic configuration of nearest noble gas and will become negatively charged ion called anion Cl-.

If there are 4 electrons in the outermost shell/valence shell of an atom, then, atom will share these electrons with other atom to acheive stable electronic configuration of nearest noble gas.

For example, Carbon atom in methane.

Atomic number of carbon is 6. Its electronic configurtion is 2, 4. It has 4 electrons in its outermost shell. Carbon atom will share these 4 electrons with other atom like hydrogen and will form covalent bond. The compond will be formed is methane with the molecular formula CH4.