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# Quantum Number

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Definition: Energy levels of electron in an atom are indicated by integers called quantum number. In an atom, the relative distance of electron from the nucleus, types of orbital, and direction of spin is shown by the quantum numbers. They are divided into 4 types.
Principal quantum number
Angular momentum quantum number
Magnetic quantum number
Spin quantum number.

Principal quantum number (n):

It indicates the value of energy level and the order, n = 1, 2, 3… and so on but not zero.

It determines the total energy (En) of an atom and ions containing one electron. It indicates the relative distance of electrons having different n values in multi-electron atom from nucleus. An electron having higher value of n is away from a nucleus compared to another electron having a lower value of n in the same atom.

n = 1,  Orbit or shell is K
n = 2,    Orbit or shell is L
n = 3,  Orbit or shell is M
n = 4,  Orbit or shell is N

Angular momentum quantum number (l):

It relates to principal quantum number and has value zero to (n-1) integer.
l = 1,  the orbital is s

l = 2,    the orbital is p

l = 3,  the orbital is d

l = 4,  the orbital is f
The values of
l determine the angular momentum of an electron which has kinetic energy due to angular motion.

The shapes of orbital are determined by angular momentum quantum number.

Magnetic quantum number (m):

It describes orientation of orbital in space under magnetic field which obtained due to angular momentum of electron and thus it relates to the value of l.
m = 2
l + 1   (values of l = +1 to -1 including zero)

l = 0,  m = 0  the orbital is s

l = 1,   m = +1, 0,-1  the orbital is p

l = 2,  m = +2, +1, 0,-1, -2  the orbital is d

l = 3,  m = +3, +2, +1, 0,-1, -2, -3  the orbital is f

The number of value of m determines the number of orbital of a particular type.

Spin quantum number (s):

Electron has two types of velocity – orbital velocity and axial velocity. Orbital velocity is velocity obtained by movement of electrons around nucleus. Axial velocity is velocity obtained by movement of electrons around its own axis.

Electron revolves clockwise and anticlockwise around its own axis and produce magnetic field. This is shown by spin quantum number and value of spin quantum number is +1/2 or -1/2

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