The correct trend in the first ionization enthalpies of the elements in the 3rd period of periodic table is :
- Si < S < Al < P < Cl
- Al < Si < S < P < Cl
- S < Si < Al < P < Cl
- Al < S < P < Si < Cl
Answer
(2) Al < Si < S < P < Cl
Solution
Across period 3, i H1 generally increases (nuclear charge increases, size decreases).
Al (3s2 3p1): the single 3p electron is well shielded and easily removed lowest
P (3s2 3p3): stable half-filled 3p subshell higher than S (3s2 3p4), where the paired electron is removed easily
Values ( kJ mol-1): Al 577, Si 786, S 999, P 1011, Cl 1255
Al < Si < S < P < Cl
Answer: (2)