Question

Explain the trend of the following in group 13 elements:

ionization enthalpy

Answer 1

1. Ionization enthalpies show an irregular trend in the group 13 elements.
2. As we move down the group, effective nuclear charge decreases due to the addition of new shells in the atom of the elements which leads to an increased screening effect. Thus, it becomes easier to remove valence shell electrons, and hence, ionization enthalpy decreases from B to Al as expected.
3. However, there is a marginal difference in the ionization enthalpy from Al to Tl.
4. The ionization enthalpy increases slightly for Ga but decreases from Ga to In. In the case of Ga, there are 10 d-electrons in its inner electronic configuration which shield the nuclear charge less effectively than the s and p-electrons and therefore, the outer electron is held fairly strongly by the nucleus. As a result, the ionization enthalpy increases slightly.
5. Number of d electrons and the extent of screening effect in indium is the same as that in gallium. However, the atomic size increases from Ga to In. Due to this, the first ionization enthalpy of In decreases.
6. The last element Tl has 10 d-electrons and 14 f-electrons in its inner electronic configuration which exerts still smaller shielding effect on the outer electrons. Consequently, its first ionization enthalpy increases considerably.