Class 11 Chemistry Structure of Atom Quantum Mechanics


It was given by Schrodinger. He said if we take both the characters in account that is particle character and wave character, we have to define a property that is a wave function.

Schrodinger wave equation

On the basis of it Schrodinger simplified equation as:


Physical significance of wavefunction:

  • It gives the amplitude associated with it. But if we do square of it, than it gives the probability of finding the electron in particular region.

Orbital: It is three-dimensional space, where probability of finding an electron in maximum.



Difference between orbit and orbital:


Orbital: They are of four types

  • s orbital: Spherical in shape, non-directional. It has only 1 orbital therefore, can accommodate only 2 electrons.
  • P-orbital: dumb-bell shaped and directional. It has 3 orbital (px, py, pz). It can accommodate maximum of 6 electrons.
  • d-orbital: It has double dumbbell, directional. It has 5 orbital (dxy,dyz,dzx,dx2-y2,dz2).It can accommodate maximum of 10 electrons
  • F-orbital: It has diffused shape. It has 7 orbital therefore, can accommodate maximum of 14 electrons.


Quantum numbers

They are set of 4 numbers, which give complete information about the address of electron.

There are 4 types of quantum numbers:

  • Principal quantum number.
  • Azimuthal quantum number.
  • Magnetic quantum number.
  • Spin quantum number.

Principal quantum number:

  • It is represented as ‘n’.
  • It was given by Bohr.
  • It represents the orbit where electron is going to be present.


  1. It gives number of electron in orbit by formula 2 n2.
  2. It gives angular momentum of electron.
  3. It gives energy of electron.
  4. It gives radius of orbit.


  1. Azimuthal quantum number:
  • It gives information about sub shell of an atom.
    • It is represented as ‘l’.
    • It was introduced by Somerfield.
    • It always has value (n-1).

Example: if n=1 ,l=0

If n=2,l=0,1

If n=3,l=0,1,2


  1. Magnetic quantum number:
  • It describes the behavior of electron in magnetic field.
  • It is represented as ‘m’.
  • It was given by land.
  • Its value is equal to –l,0, +l

For example: if n=1, l=0, m=0 that is only one orbital

If n=2, l=0,1, m=-1,0, +1 that is three orbitals


  1. Spin quantum number:
    • It gives the info about spinning of electron about its axis i.e. clockwise or anticlockwise
    • It is denoted by ‘s’.
    • Its value is either =+1/2, -1/2

          Problem: Write down the quantum numbers n , l and m for the

          Following orbitals:

  1. 3d x2 y2
  2. 4d z2   

Answer :-

n=3, l=2, m=+2

N = 4, l=2, m=0

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