Question

what is meant by quantum number

Answer 1

Quantum Number Definition

A quantum number is a value that is used when describing the energy  levels available to atoms and molecules . An electron  in an atom or ion has four quantum number to describe its state and yield solutions to the Schrödinger wave equation for the hydrogen atom.

Answer 2

Quantum numbers are the numbers which give us the information about the location , the shell , sub shell , orbitals to which the electrons of an atom belongs to and quantum numbers also gives us the information about the various energy  levels and distance between the electrons from the nucleus , it also gives information about the nodes of electrons etc
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there are 4 types of quantum numbers

1)principal quantum number 
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1)it represents the main shell  to which an electron belong and also the approx energy , approx distance between the nucleus and an electron
2)it is represented by the letter 'n'
3)where 'n' =1 2 3 .............
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2)azimuthal quantum number
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1)it represents the subshell to which an electrons belong
2)it also determines the shape and angular momentum of electrons
3)it is represented by letter l
4)where l = (n-1)
5)it is also called as orbital angular momentum quantum number, orbital quantum number or second quantum number
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3)magnetic quantum number 
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1)it represents the orientation of the atomic orbitals around the nucleus 
2)it is represented by the letter 'm'
3)where no of values for m =( 2l +1)
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4)spin quantum number
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1)it says how do the electrons revolve around the nucleus weather clock wise or anti clockwise
2)it is represented by letter s
3)its values are +1/2 or -1/2
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