Question

7. The following is the Lewis dot structures (that is satisfying octet rule) for sulfate ions, SO42-, (1) Calculate the formal charge of the Sulfur and oxygen atoms. (2) Update the Lewis structure to one that have the most favorable formal charge. (S ?s in 3rd period and can possess expanded octet)

Answer 1

1) According to the given Lewis structure sulphur has formal charge = +2 because unbonded atom has 6 electrons, 4 used in forming 4 bonds and no lone pair shown on S.

each oxygen has one negative formal charge , as each of them have 3 lone pairs,and one bonded electron to their share. hence formal charge =6-(6+1) = -1

Total charge on the species = sum of formal charges = +2 -4 = -2

2) The structure that has most favorable formal charge is

In this structure , sulphur has no formal charge , two oxygens having double bonds also no formal charge, the remaining two oxygens have one negative formal charge.

   formal charge of sulpur= 6-( 6) = 0

formal charge of oxygens with double bond = 6-[2x2 +2(bonded electrons)]= 0

formal charge of xygens with single bond = 6- [3x2 + 1] = -1

(unable to show the lone pairs in diagram)