JEE MAIN - Chemistry (2006 - No. 37)
The increasing order of the first ionization enthalpies of the elements B, P, S and F (lowest first) is :
F < S < P < B
P < S < B < F
B < P < S < F
B < S < P < F
Explanation
The correct order of ionisation enthalpies is $$F > P > S > B$$
NOTE : On moving along a period ionization enthalpy increases from left to right and decreases from top to bottom in a group. But this trend breaks up in case of atom having fully or half filled stable orbitals.
In this case $$P$$ has a stable half filled electronic configuration hence its ionisation enthalpy is greater in comparison to $$S.$$ For B(5) electronic configuration is = 1s22s22p1 and P(15) electronic configuration is = 1s22s22p63s23p3. As P has half filled valence shell so removing electron will be harder compare to B. Hence by checking all options the correct possible order is
B < S < P < F
NOTE : On moving along a period ionization enthalpy increases from left to right and decreases from top to bottom in a group. But this trend breaks up in case of atom having fully or half filled stable orbitals.
In this case $$P$$ has a stable half filled electronic configuration hence its ionisation enthalpy is greater in comparison to $$S.$$ For B(5) electronic configuration is = 1s22s22p1 and P(15) electronic configuration is = 1s22s22p63s23p3. As P has half filled valence shell so removing electron will be harder compare to B. Hence by checking all options the correct possible order is
B < S < P < F
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