b)
- For subshells with the same value of (n+ℓ), electrons are assigned first to the sub shell with lower n.
- A version of the aufbau principle known as the nuclear shell model is used to predict the configuration of protons and neutrons in an atomic nucleus.
Now we take a question to understand it clearly:
Q. n and l values of an orbital A are 3 and 2 and for other orbital B are 5 and 0. The energy of :
A) B is more than A
B) A is more than B
C) A and B are same
D) A is 4 times than B
Sol. Electrons are assigned to orbitals in order of increasing value of (n+l). For subshells with the same value of (n+l), electrons are assigned first to the subshell with lower n.
For orbital A,n = 3, l = 2, therefore, n+l=5
For orbital B,n = 5, l = 0, therefore, n+l =5
So, larger the n, greater is the energy.
So, the energy of B > energy of A.
c) (i)
- The exactly half-filled and fully filled orbitals have greater stability than other configurations.
- The reason for their stability are symmetry and exchange energy.
- The half-filled and fully-filled orbitals are more symmetrical than any other configuration and symmetry leads to greater stability.
(ii)
- The half-filled and fully-filled orbitals are more symmetrical than any other configuration and symmetry leads to greater stability.
- The electrons present in the different orbitals of the same sub-shell can exchange their positions.
- Each such exchange leads to the decrease in energy known as Exchange Energy