Question

The electron identified by quantum number n and l

1. n=4, l=1 2. n=4, l=0

3. n=3, l=2 4. n=3, l=1

Can be placed in the order of increasing energy from the lowest to highest as

A) 4<2<3<1 B) 2<4<1<3

C) 1<3<2<4 D) 3<1<4<2

Answer 1

According to Aufbau principle,
(i) Greater the (n+l) value, greater the energy of the orbital.
(ii) For sub-shell with the same value of (n+l), greater the "n" value, more will be the energy.
Hence, energies of above mentioned orbitals are in the order of
(1) n = 4, l = 1 ⇒ 4p orbital, (n+l)= 5
(2) n = 4, l = 0 ⇒ 4s orbital, (n+l)= 4
(3) n = 3, l = 2 ⇒ 3d orbital, (n+l)= 5
(4) n = 3, l = 1 ⇒ 3p orbital, (n+l)= 4

3p < 4s < 3d < 4p.