L3 Che101

Department of Mathematics and Natural Sciences
Content: Different quantum numbers, orbit and orbital,

electronic configurations
Quantum Numbers
Quantum numbers are a set of values that describes the state of an electron
including the size of an electron orbit (energy levels), the shape of the orbitals,
orientation of orbital in the magnetic field and the spin of electrons about its
own axis.
The above four characteristics are represented by

four Quantum Numbers
i. Principal quantum number (n)
ii. Azimuthal or subsidiary quantum number (l)
iii. Magnetic quantum number (ml)
iv. Spin quantum number (ms)
i) Principal quantum number (n)
Express Number of energy level
distance of
size of
Indicates orbit from
orbit (n = 1)
nucleus
(n = 2)
Energy of
electrons (n = 3)
total number of electrons

Determine
in a shell (by 2n2)
K L M N …..
Shells are designated by
letters also
1 2 3 4 …..
Orbit
▪ In an atom electrons move around the nucleus in a two dimensional, spherical
fixed energy levels which is called the orbit.

▪ The orbit nearest to the nucleus is the first energy level and is called ‘K shell’. The
next orbits are named as L, M, N and so on.
ii) Azimuthal quantum number (l)
Concepts of orbitals of
Express
different shapes
possible 0 to (n-1)
values of l e.g. n = 3, l = 0, 1, 2
Indicates shapes of orbitals in a shell
total number of electrons in an

Determine
orbital as 2(2l+1)
Subshells are denoted Letter s p d f g …

by letters as
l 0 1 2 3 4 ...
Maximum number of
electrons
2 6 10 14
Orbital
The three dimensional region in space around the nucleus where the probability of
finding an electron is maximum (90-95 %) is called orbital. These are s,p,d,f.

iii) Magnetic quantum number (ml)
orientation of orbitals in 3
indicates dimensional space
-l through 0 to +l
allowed
For l = 0, ml = 0 (s subshell)
values
For l = 1, ml = -1, 0, +1 (p subshell)
total number of orbitals in a

Determine
subshell
Different types of orbitals
There are four types of orbital: s, p, d and f
1) s-orbital is spherical shaped with nucleus at the center
2) p-orbital is dumbbell shaped
❖ It’s divided into three orbital with same energy
❖ They are px py, pz
❖ They lie on x, y and z axis perpendicular to each other
3) d-orbital - there are five different orbitals
4) f-orbital - there are seven f orbitals

Shapes of different types of orbital
s-orbital
(spherical shape)
p-orbitals (dumbbell shaped)

Different types of orbital with different
quantum numbers
s
l=0, m=0
l=1, m=-1 l=1, m=0 l=1, m=+1

Difference between orbit and orbital
Orbit Orbital
Orbits are definite path or energy level The three dimensional region in space
followed by an electron, according to Bohr around the nucleus where the probability of
finding an electron is maximum (90-95 % )
is called orbital.
It is represented two dimensionally. An orbital is three dimensional
representation.
The orbits may be circular or elliptical. Different orbitals have different shapes.
e.g. s orbital spherical, p orbital dumbbell
shaped
Two orbits in an atom cannot have the Two orbitals can have the same energy
same energy. e.g., px py, pz have the same energy.
An orbit can hold 2n2 number of electrons Each orbital can hold maximum two
where n is the principle quantum number electrons of opposite spin e.g. s orbital
having the values 1, 2, 3 etc. holds 2, three p orbitals hold 6 and 5d
orbitals hold 10 electrons.
iv) Spin quantum number (ms)
Two possible orientation of the spin
indicates
axis of an electron
possible values +1/2 or -1/2 for each value of m

Quantum Numbers
Quantum Numbers
Quantum Numbers & related informations
Q: Determine the values of the missing
quantum numbers and sublevel names.
n l ml Name
(i) ? ? 0 4p
(ii) 2 1 0 ?
(iii) 3 2 -2 ?
(iv) ? ? ? 2s
DIY
Q: According to the concept of the quantum numbers which of
the following orbitals are possible and which are not? Give
possible explanation against your reasons.
i) 2p ii) 2d iii) 3d iv) 1p
Q: Explain why each of the following sets of quantum numbers

is not permissible for an orbital
(i) n = 0, l = 1, ml = 0, ms = +1/2
(ii ) n = 3, l = 2, ml = +3, ms = -1/2

Electronic Configuration
of Atoms
In an atom the electrons are held in different orbits, sub-shells
and orbital in a regular way. This arrangement of electrons in
an atom is called the electronic configuration.
Principles that influence the electronic configuration of atom:

⮚ Pauli’s exclusion principle
⮚ Aufbau principle
⮚ Hund’s rule
Wolfgang Pauli 1900-1958
Nobel Prize in Physics

1945
"for the discovery
of the Exclusion
Principle, also
called the Pauli
Principle."
Pauli’s exclusion principle
According to this principle, ‘no two electrons in the same atom can
have the same values for the four quantum numbers’.
For example, He (helium) had two electrons in 1s orbital and their electronic
configuration is 1s2, that means they had two electrons in the 1s orbital. This two
electrons can have same values for three of their quantum numbers, but the fourth
quantum number must be different for the two electrons.
Electronic configuration of helium atom is:

He (2) = 1s2
For the first electron, n = 1, l = 0, ml = 0, ms = +1/2

And for the second electron, n = 1, l = 0, ml = 0, ms = -1/2
So, these two electrons have different values of their spin quantum
number.
Aufbau principle
According to this principle, ‘the electrons will first occupy the
lowest energy levels’.
❖ The energy of the levels are determined by their (n + l) values.
❖ The electron will first occupy the orbital having the lowest value of (n + l)
Q. In which orbital the electron will

go first if the values of (n + l) is same
for both of the orbital?
Ans: In that case the electron goes to
the orbital with lowest value of ‘n’.
Figure: Filling of electrons in various

orbitals according to (n+1) rules
Increasing order of energies of the atomic
orbitals:
1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s…………
Friedrich Hund 1896-1997
Max Planck Medal in

Physics 1943
Hund’s rule
According to this rule, ‘electron pairing in any orbital of same sub
level will not occur until each orbital contains one electron’.
For example:
Electronic configuration of nitrogen atom is: N (7) = 1s2 2s2 2px1 2py1 2pz1
The electrons of p orbital will be equally distributed in three p orbital ant the configuration
of N will be:
O (8) = 1s2 2s2 2px2 2py1 2pz1
The fourth electron become paired up in px and is of opposite spin as electron of

same spin repel each other.
Electronic configuration of elements following Hund’s rule
List of Electron Configurations of Elements
(sciencenotes.org)
Periodic Table - Ptable

L3 Che101

Uploaded by

Copyright:

Available Formats

L3 Che101

Uploaded by

Document Information

Original Description:

Original Title

Copyright

Available Formats

Share this document

Share or Embed Document

Sharing Options

Did you find this document useful?

Is this content inappropriate?

Copyright:

Available Formats

L3 Che101

Uploaded by

Copyright:

Available Formats

Department of Mathematics and Natural Sciences

Content: Different quantum numbers, orbit and orbital,

The above four characteristics are represented by

total number of electrons

fixed energy levels which is called the orbit.

Indicates shapes of orbitals in a shell

total number of electrons in an

Subshells are denoted Letter s p d f g …

finding an electron is maximum (90-95 %) is called orbital. These are s,p,d,f.

total number of orbitals in a

1) s-orbital is spherical shaped with nucleus at the center

2) p-orbital is dumbbell shaped

❖ It’s divided into three orbital with same energy

❖ They are px py, pz

❖ They lie on x, y and z axis perpendicular to each other

3) d-orbital - there are five different orbitals

4) f-orbital - there are seven f orbitals

p-orbitals (dumbbell shaped)

l=1, m=-1 l=1, m=0 l=1, m=+1

possible values +1/2 or -1/2 for each value of m

i) 2p ii) 2d iii) 3d iv) 1p

Q: Explain why each of the following sets of quantum numbers

(ii ) n = 3, l = 2, ml = +3, ms = -1/2

Principles that influence the electronic configuration of atom:

Nobel Prize in Physics

Electronic configuration of helium atom is:

For the first electron, n = 1, l = 0, ml = 0, ms = +1/2

Q. In which orbital the electron will

Figure: Filling of electrons in various

Max Planck Medal in

O (8) = 1s2 2s2 2px2 2py1 2pz1

The fourth electron become paired up in px and is of opposite spin as electron of

Periodic Table - Ptable

You might also like