Region around the nucleus of an atom where probability of finding electron is maximum or where the electron density is maximun is called orbit or Energy level or shell.
Representation Of Orbits or Energy Levels or Shells:-
Bohr represented Orbits or energy levels or shell's by the capital letters of alphabet as K, L, M, N, O, P, Q shells.Sub Orbit or Sub Energy Level or Sub Shell:-
Different spaces of an orbit or Energy level or shell where electron revolves with different energy are called sub orbits or sub energy levels or sub shelle. There are four orbits or sub energy levels or sub shells given below:Four Sub orbits Sub energy levels or sub shells:-
• S- sub shell
• p - sub shell
• d - sub shell
• f - sub shell
s stand for sharp
p stand for principle
d stand for diffuse
f stand for fundamental.
Orbitals:-
Orientation of a sub shell in space or directions of motion of electrons in space in a sub shell are called orbitals.Orbital of S- Sub Shell:-
There is one orbital of s- sub shell, which is spherical in shape.
Orbitals of P- Sub Shell:-
There are three orbital of p- sub shell, which are called px, py and pz and are dumbbell in shape.
Orbitals of d- Sub Shell:-
There are five orbitals of d-sub shell, which are dxy, dyz, dxz, dx^2y^2 and dz^2 difficult to give names of seven orbitals in three dimensional space.
Quantum Numbers:-
Numbers or integral which shows the behaviour of an electron in an atom are called quantum numbers. There are four quantum numbers which are given below:1) Principle Quantum Number (n):
• Principle quantum numbers shows the number of orbitals and energy levels, size of shells and energy of shells. Greater the value of n larger the size of shell and more will be the energy.
• Its shows the number of sub shell and sub energy levels in the shell or energy level, and it is equal to the value of n for a shell.
• Value of n shows the number of electron to be filled in the shell of energy level it is equal to 2n^2
2) Azimuthal Quantum Number or Subsidiary Quantum Number (l) :-
• value of l is depend on the value of n its from the 0 to n-1.
• value of l show the number of sub shell in a shell, thus for k, L, M and N value of l are (0), two (0,1), three (0,1,2) , four (0,1,2,3) so they have one (s) two (s,p) three (s,p,d) four (s,p,d,f).
• Value of l is 0 for s, 1 for p, 2 for d, 3 for f sub shell.
• value of l shows the number of electron to be filled in a sub shell. It is equal to l+2 thus in s we can fill 4(0) + 2 = 2 electrons, in p we can fill 4(1) + 2 = electrons, in d we can fill 4(2) + 2 = 10, in f we can fill 4(3) + 2 = 14 electrons.
• Value of l shows number of orbitals in sub shell it is equal to 2l + 1. Thus s has 2(0) + 1 = 1 orbitals, p has 2(1) + 1 = 3 orbitals (px, py, pz), d has 2(2) + 1 = 5 orbitals and f has 2(3) + 1 = 7 orbitals.
3)Magnetic Quantum Number (m):
This quantum number shows the magnetic property of an element in an orbital under the influence of an external magnetic field. Its shows the number or orientations of a sub shell in space.
Value of (m):-
Value of m depened on the value of l and s from +l to 0 to -l. Values of m for s, p, d and f are given below:
For s, l = 0 thus m = 0, for p, l = 1 thus m = +1, 0, -1, for d l = 2 thus m = +2, +1, 0, -1, -2 and for f, l = 3 thus m = +3, +2, +1, 0, -1, -2, -3.
4) Spin Quantum Number (s):
This quantum number shows the spin of an electron in an orbital. If there is one electron in an orbital than 50% probability for it is to spin clockwise and 50% to spin anticlock wise, so value of s for it is +1/2 or -1/2. But if there are two electrons in an orbital then always one spins clockwise and other anticlock wise, so the value of s for one electron is always +1/2 and for other always -1/2.
Paulli's exclusion Principle:-
Definition:-No two electron in an orbital have same values of all the four quantum numbers.
Expanation:-
According to Paulli's exclusion principle if two electron are present in the same orbital then they can not have same values for all the four quantum numbers.
They have same values of first three quantum numbers which are for the orbital, but always value of fourth spin quantum number is different because one electron move clock wise and other moves anticlock wise.
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