it is given that ionisation enthalpy of carbon is more than that of beryylium due to its comparitively small size shouldnt beryllium have higher ionisation enthalpy  due to its fully filled s subshell ???

Asked by Viswanath | 15th Aug, 2014, 11:12: AM

Expert Answer:

  • Ionisation energy of Be (Z = 4 1s22s2) is less than that of C (Z = 6 1s22s2 2p2) because the nuclear charge of C is greater than Be and the atomic size of C (77 pm) is smaller than Be (152 pm).
  • Higher the nuclear charge, greater would be the force of attraction between the nucleus and outermost electrons and thus more energy is required to remove the electrons.
  • Hence, the  I.E of C(1088 kJmol-1 ) would be greater than that of Be ( 899 kJmol-1).

Answered by Vaibhav Chavan | 18th Aug, 2014, 11:19: AM