What is the order of ionisation enthalpy of group 13 elements ?
Dear Student,
Ionisation enthalpy decreases as we move down the group. This is due to increase in atomic size and screening effect which is more than to compensate the effect of increase in nuclear charge. Consequently, the electron becomes less and less tightly held by the nucleus as we move down the group. Hence , ionisation enthalpy decreases down the group.
The increasing order of atomic size is as follows : B < Al < Ga< In < Tl
So the expected decreasing order of ionisation enthalpy is as: B > Al > Ga > In > Tl
However, ionisation enthalpy of Ga is greater than that of Al. In the case of Gallium, there are ten d-electrons in its inner electronic configuration. Since the d-electrons shield the nuclear charge less effectively than the s- and p-electrons, the outer electron is held fairly strongly by the nucleus. As a result, the ionisation enthalpy increases slightly. The similar increase is observed from In to Tℓ, which is due to the presence of 14 f-electrons in the inner electronic configuration of Tℓ which have very poor shielding effect.
Therefore, the order becomes : B > Ga > Al > Tl > In
Ionisation enthalpy decreases as we move down the group. This is due to increase in atomic size and screening effect which is more than to compensate the effect of increase in nuclear charge. Consequently, the electron becomes less and less tightly held by the nucleus as we move down the group. Hence , ionisation enthalpy decreases down the group.
The increasing order of atomic size is as follows : B < Al < Ga< In < Tl
So the expected decreasing order of ionisation enthalpy is as: B > Al > Ga > In > Tl
However, ionisation enthalpy of Ga is greater than that of Al. In the case of Gallium, there are ten d-electrons in its inner electronic configuration. Since the d-electrons shield the nuclear charge less effectively than the s- and p-electrons, the outer electron is held fairly strongly by the nucleus. As a result, the ionisation enthalpy increases slightly. The similar increase is observed from In to Tℓ, which is due to the presence of 14 f-electrons in the inner electronic configuration of Tℓ which have very poor shielding effect.
Therefore, the order becomes : B > Ga > Al > Tl > In