The arrangement of orbitals on the basis of energy is based upon their (n+l) value. Lower the value of (n+l), lower is the energy . For orbitals having same values of (n+l). The orbital with lower value of n will have lower energy.
I. Based upon the baove information arrange the following orbitals in the increasing order of energy.
(a) 1s,2s,3s,2p (b) 4s,3s,3p,4d
(c) 25p,4d,5d,4f,6s (d) 5f,6d,7s,7p
II. Based upon the above information Solve the question. give below.
(a) hich of the following orbitals has the lowest energy
`4d,4f,5s,5p`
(b) which of the following orbitals has the higher energy?
`5p,5d,5f,6s,6p`

Explanation

(i) The statement represents Aufbau principle (n+l) rule :
(a) 1s=1+0=1 , 2s=2+0 , 2p=2+1 = , 3s = 3+0=3
The increasing order of energy : `1s lt 2s lt 2p lt 3s`.
(b) 3s=3+0=3 , 3p=3+1 =4 , 4s =4+0=4 , 4d = 4+2=6
The increasing order of energy : `3s lt 3p lt 4s lt 4d`.
(c) 5p = 5+1=6 , 4d=4+2=6 , 5d=5+2=7 , 4f = 4+3=7 , 6s = 6+0=6
The increasing order of energy : `4d lt 5p lt6s lt4f lt 5d`.
(d)` 5f=5+3=8 , 6d = 6+2=8 , 7p=7+0=7 , 7p=7+1=8`
The increasing order of energy `: 7s lt 5f lt 6d lt 7p`.
(ii) (a) 5s orbital with least (n+l) value (5+0)=5 has the lowest energy.
(b) 5f orbital with maximum (n+l) value (5+3)=8 has the highest energy.