Question

The ionisation enthalpy also depends upon the electronic configuration of the atom. It has been  observed that certain electronic configurations are more stable than others. For example half filled and  completely filled shell have extra stability associated with them. Consequently it is difficult to remove  electron from these stable configurations.  Answer the following on the basis of the above paragraph:  (i) Why the noble gases have highest value of ionisation enthalpies in their respective period ?  (ii) Out of Li, Be, Mg, Al, P and Cl which have completely filled and half-filled orbitals consequently  large ionisation enthalpies​

Answer 1

The answers are:

• The noble gases have highest value of ionization enthalpies in their respective period because they have extra stability as compared to others in the same period due to attaining a completely filled octet in the outer shell.
• Elements with half filled orbitals = Li, P.
• Elements with completely filled orbitals = Be,  Mg.
• None of them= Al and Cl.
• The electronic configuration of the various elements are given below which help us to decide that whether they have half filled orbitals or full filled orbitals or neither of them.

1.Li : 1s² 2s¹ ( half filled orbitals)

2. Be : 1s² 2s² ( full filled orbitals)

3. Mg : 1s² 2s² 2p⁶ 3s² ( full filled orbitals)

4. Al : 1s² 2s² 2p⁶ 3s² 3p¹ (none of them)

5. P : 1s² 2s² 2p⁶ 3s² 3p³ (half filled orbitals)

6. Cl : 1s² 2s² 2p⁶ 3s² 3p⁵ (none of them)

Answer 2

Question 1:

Why the noble gases have highest value of ionisation enthalpies in their respective period ?

Answer:

• The ionization enthalpy of any element depends upon the amount of energy required to remove an electron from the the valence shell.

• Now , in a particular period noble gases have the maximum stability because of their complete octet configuration in their valence shell.

• So, noble gases do not have any intention to change their stable state.

• Hence, a very large amount of energy is required to remove a single electron from valence shell of noble gases.

• So, Ionisation enthalpy is very high.

Question 2:

Out of Li, Be, Mg, Al, P and Cl which have completely filled and half-filled orbitals consequently  large ionisation enthalpies?

Answer:

In this question , let's see the electronic configuration of each of the elements given in the question :

1. Li : 1s² 2s¹ (hence half filled orbital)

2. Be : 1s² 2s² (hence full filled orbital)

3. Mg : 1s² 2s² 2p⁶ 3s² (hence full filled orbital)

4. Al : 1s² 2s² 2p⁶ 3s² 3p¹ (no half /full filled orbital)

5. P : 1s² 2s² 2p⁶ 3s² 3p³ (half filled orbital)

6. Cl : 1s² 2s² 2p⁶ 3s² 3p⁵ (no half/full filled orbital)

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