how can i memorise the vlancies for writing a chemical formula \? i feel this is tough

Asked by snborah | 12th May, 2014, 11:21: PM

Expert Answer:

The key for learning valency is to understand it rather than mugging.

Valency of an element represents the combining capacity of the element.

Or Valency of an element can be defined as the number of electrons lost, gained or shared by its atom during chemical combination.

There are few skills you have to develop in this area:

  • Starting from the basics, you should be aware of all the symbols and atomic numbers of elements.
  • The valence electrons of an atom determine the valency of that element.
  • The number of valence electrons varies from 1 to 8 for the atoms of the different elements.
  • Atoms react with each other to achieve an octet in their valence shell. Atoms complete their octets by sharing, accepting or donating electrons.
  • If the atom has more than 4 electrons in its outermost shell then the atom will gain electrons and to achieve inert gas configuration and will become negatively (-) charged ion called anion.
  • 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 achieve stable electronic configuration of nearest noble gas and will become negatively charged ion called anion Cl_. Valency of chlorine is -1.
  • 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.
  • Sodium with atomic number 11 and electronic configuration 2, 8, 1 has one electron in its outermost shell. It will lose this electron to achieve inert gas configuration and will become positively charged cation Na+. Valency of chlorine is +1.
  • If the atom has exactly 4 electrons in its outermost shell then the valency of atom will be 4.

Using the valency of the ions we can write the formulae of compounds.

Answered by Hanisha Vyas | 14th May, 2014, 10:27: AM