Name: The d-block Elements
Uploaded: 2019-07-19
Duration: 8 min 21 s
Description: The periodic table started with elements arranged in increasing order of Z. Now, it can tell us much more about an element. Watch this video to learn more.

Question

How would you account for irregular variation of 1st and 2nd ionisation enthalpies in the 1st series of transition elements?

Accepted Answer

In the first transition series, ionization enthalpy increase from left to right due to the continuous filling of electrons in $d$ orbital. The irregular variation occurs in ionization enthalpy is due to the extra stable configuration of elements like $d^{5}, d^{10}$ . Since these states are stable so, their ionization enthalpy is high.

In case of first ionization energy, $Cr$ has low ionization energy. This is because after losing one electron, it attains the stable configuration $(3 d^{5})$ . On the other hand, $Zn$ has exceptionally high first ionization energy as an electron has to be removed from stable and fully filled orbitals $(3 d^{10} 4 s^{2})$ .

The second ionization energy is higher than the first ionization enthalpy. Elements like $Cr$ and $Cu$ have exceptionally high second ionization energies as after losing the first electron, they have attained the stable configuration. Hence, taking out one electron more from this stable configuration will require a lot of energy.

How would you account for irregular variation of 1st and 2nd ionisation enthalpies in the 1st series of transition elements?

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