Question

Exchange energy of an electron is the energy released when it exchanges its position with?
A. The electron having opposite spin present in non-degenerate orbitals
B. The electron having same spin present in degenerate orbitals
C. The electron having same spin present in non-degenerate orbitals
D. The electron having opposite spin present in degenerate orbitals

Answer 1

Hint: In chemistry, the exchange interaction is a quantum mechanical effect that only occurs between identical particles.

Complete step by step answer:

The exchange energy is the energy released when two or more electrons with the same spin exchange their positions in the degenerate orbitals of a subshell.
Significance - From above,you have got exchange energy definitions. Now Let's explain its significance:
Exchange energy = Calculated Orbital energy - Actual Orbital energy when electrons are present
You can see an increase of exchange energy would decrease actual orbital energy since calculated orbital energy is fixed. Less actual orbital energy means the orbital is more closer to the nucleus than it should be. Thus electrons are more tightly bound which gives extra stability of electrons of valence shell.
Exchange phenomena is only possible for valence shell orbitals where electron exchange is possible. Pairing of electrons decreases exchange energy to some extent.

Hence, we can conclude that the correct option is B.

Additional information: The exchange energy increases with the number of electrons with same spin
Exchange energy, $E\quad =\quad \dfrac { K\times n\times (n-1) }{ 2 } $
n= no. of electrons with the same spin.
K= exchange constant (different for different metals)
Now, as in the half filled configuration, the number of electrons with same spin i.e. n is maximum for the degenerate orbitals of a particular subshell, thus, the exchange energy is maximum for this configuration and thus stabilizes the most.
e.g. Cr (24) takes ${ d }^{ 5 }$ configuration instead of ${ d }^{ 4 }$ to gain more stabilization due to exchange energy.

Note: Exchange energy forms an important part of the covalent bond of many solids and is also responsible for ferromagnetic coupling.
Exchange energy decreases when you move from top to bottom in a group as in the bottom group elements, the nucleus the valence electrons have already a large amount of space to move owing to their presence in big orbitals and hence, they do not need the help of exchange energy.