Question

Arrange the following in increasing order of radii:
a) $I,I^{+},I^{-}$
b)$C,N,Si,P$

Answer 1

• a)Cations are always smaller than their parent atoms this is because they have lesser electrons, while their nuclear charge remains the same. The remaining electrons are, therefore held more tightly by the protons in the nucleus and thus their radii.are smaller than the parent atoms. This is opposite in case of anions.
  
• Hence the correct order:$I^{+}<I<I^{-}$

b)Correct Order of atomic size:$N<C<S<P$

• Going down the group, due to increase in number of shells, atomic size increases hence P and S have relative greater sizes. {s-block metals are realtively large.]
  
• Across the period from left to right, atomic size decreases due to increase in effective nuclear charge hence Carbon atom and Sulfur atom are larger than the Nitrogen atom and Phosphorus atom respectively.