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### Quantum numbers

Quantum numbers are the address of electrons. These are numbers used to specify the position and energy of electrons in an atom. Four quantum numbers are usually used to designate the electrons present in an orbital.
1. Principal quantum number(n)
2. Azimuthal quantum number(l)
3. Magnetic quantum number(m)
4. Spin quantum number(s)
1. Principal quantum number(n)
This represents the main shells in an atom. It determines the size and energy of orbitals. It can have any positive value from 1 to infinity. Shells are designated as K, L, M, N etc., When n= 1, 2, 3, 4....etc respectively.
2. Azimuthal quantum number(l)
This represents the sub shell. It determines the shape of orbitals It also gives the orbital angular momentum quantum number. 'l' may have values from 0 to (n-1). If the principal quantum number n=1, 'l' has a value of '0', there will be only 's' subshell.
3. Magnetic quantum number(m)
This represents the orbitals. ie, the orientation of orbitals in sub shells. 'm' can have values from -l to +l including '0'. That is for an 'l' value, there are (2l+1) values for 'm'. If l=1 (p-sub shell), 'm' will have 3 values; m= +1, 0, -1. This means that 'p' sub shell have 3 orbitals. ie, there can be three possible orientations of p-orbitals in space.
4. Spin quantum number (s)
This represents the spin direction of electron. A charged particle which spins about its own axis behaves as a small magnet. Hence spinning of an electron generates a magnetic moment which combines with the magnetic moment generated due to orbital angular momentum of electron. This combination of magnetic moments modifies the energy of the electron in an orbital. Since the electron can spin in clockwise or anti clockwise directions, the spin quantum number may have two values; +1/2 and -1/2. +1/2 indicates the spinning of electron in clockwise direction and -1/2 in anti clockwise direction.