1. Rules for filling electrons in
various orbitals
Dr. Mithil Fal Desai
Shree Mallikarjun and Shri Chetan Manju Desai College
Canacona Goa
2. Principal
quantum
number- n
Azimuthal quantum
number
0,….,(n-1)
1 0
2 0,1
3 0,1, 2
4 0,1,2,3
Azimuthal
quantum
number -l
Magnetic quantum
number ml
(-l,..0..,+l)
Orbital
0 0 s
1 -1,0,+1 p
2 -2,-1,0,+1,+2 d
3 -3,-2,-1,0,+1,+2,+3 f
Spin quantum
number -s
+½ or -½
Orbital Number of radial nodes
(n-l-1)
1s 1-0-1=0
2s 2-0-1=1
2p 2-1-1=0
3s 3-0-1=2
3p 3-1-1=1
3d 3-2-1=0
State of electron is given
by set of four quantum
numbers.
(n, l, ml, s)
3. Aufbau’s principle
The electrons are added one by
one to the various orbitals in
order of their increasing energy
starting with the orbital of
lowest energy. The increasing
order of energy of various
orbitals is
1s<2s<2p<3s<3p<4s<3d<3d<5s<
5p<6s<4f<5d<6p<7s<5f<6d<7p
1s
2s 2p
3s 3p 3d
4s 4p 4d 4f
5s 5p 5d 5f
6s 6p 6d
7s 7p
4. Pauli’s exclusion principle
No two electrons in an atom will have same value of all the four quantum
numbers.
If one electron in an atom has n = 1, l=0, m = 0, and s = +1/2, the quantum
numbers no other electron can have the same four quantum numbers.
n = 1, l=0, ml = 0, and s = +1/2
n = 1, l=0, ml = 0, and s = +1/2
1s
n = 1, l=0, ml = 0, and s = +1/2
n = 1, l=0, ml = 0, and s = -1/2
1s
n = 1, l=0, ml = 0, and s = +1/2
n = 1, l=0, ml = 0, and s = -1/2
1s
n = 1, l=0, ml = 0, and s = +1/2
5. Hund’s Rule of maximum multiplicity
Electron pairing in p, d and f orbitals cannot occur until each orbitals of a given
subshell contains one electron each or is singly occupied.
2p
2px 2py 2pz
2p
2px 2py 2pz
3- electrons in p orbital
E
n
e
r
g
y
