HOW TO DECIDE WHICH VALENCY TO BE TAKEN IN CASE OF ELEMENTS WITH VARIABLE VAlLANCY, WHILEWRITING CHEMICAL FORMULA OF A COMPOUND. FOR EXAMPLE, SULPHER IS HAVING VALENCY 2 AND 4 BUT WHILE WRITING CHEMICAL FORMULA OF SULPHER DIOXIDE. WE TAKE VALENCY 4. IN THIS CASE WHY  VALECY 2 CANNOT BE TAKEN. PLEASE EXPLAIN.

Asked by rajib.tripathi | 14th May, 2017, 12:29: PM

Expert Answer:

In case of SO2 for example:
  • Sulphur form higher oxidation state than oxygen as it can utilize all six outer electrons in bonding by promoting some of its to its higher 3d orbital.
  • But in case of oxygen, the next empty orbital is 3s which is considerable of higher energy than the highest occupied orbital 2p.
  • Oxygen can form positive oxidation state only with fluorine which is highly electronegative.
  • Hence, sulphur can show +4 oxidation state in SO2.
  • Sulphur show variable oxidation states such as +4,+5, +6 with oxygen in different compounds. Example: SO2, SO3, SO32- , SO42-.

Answered by Vaibhav Chavan | 15th May, 2017, 12:38: PM

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