Hydrogen Spectrum:-

Definition:-
Line spectrum obtained by passing the radiations emitted from the Hydrogen through a prism is called hydrogen spectrum.

Explanation (Origin of Hydrogen Spectrum):-
When hydrogen is heated its electron absorb energy and jump from lower energy level 1 to higher energy level 2,3,4,5,6 and when it jump back to the lower energy level 1 then it emit energy in the form of radiations, when these radiation pass through a prism then gives line of spectrum called Hydrogen spectrum. Each line of spectrum corresponds to a radiation.
Different scientist discover different series of lines of hydrogen spectrum which are known by their names.

Different Series of Spectral Lines of Hydrogen Spectrum:-

1) Balmer's Series:-
In 1885 Balmer found a series of lines of Hydrogen spectrum in visible region ( lemda = 4000 Angstrom to 7500 Angstrom) when elecctron jumps to higher energy levels to lower energy level 2 This series is called Balmer's series.
Wave number of the radiations in this series is calculated by formula.
Here lower energy level is 2 and higher energy levels is 3,4,5,6.

2) Layman's Series:-
Layman found a series of lines of hydrogen spectrum in ultra violet (u.v) region when electron jumps from higher energy level to lower energy level 1. This series is called layman's series. Wave number of radiation of this series is calculated by the same formula.
Here lower energy levels in 1 and higher energy levels is 2,3,4,5

3) Paschen's Series:-
 Paschen found a series of lines of Hydrogen spectrum in Infra red (I.R) region when electron is jumps from the higher energy levels to the lower the energy level 3. This series is called paschen series. Wave number of the radiation of this series is calculated by same formula. Here lower energy level is 3 and higher energy levels is 4,5,6,7.

4)Bracket's Series:-
Bracket found a series of line of hydrogen spectrum in infra red (far I.R) region when  electrons jumps from the higher energy level to the lower energy level 4 this series is called Bracket's series. Wave number of the radiations in this series is calculated by the same formula. Here lower energy level is 4 and higher energy levels is 5,6.

Pfund's Series:-
Pfund also found the series of lines of Hydrogen spectrum in far infra red (far I.R) region when electron jumps from higher energy level to the lower energy level 5 this series is called pfund's series. Wave number of the radiation of this series is calculated by same formula. Here lower energy level is 5 and higher energy level is 6.

Two Concept about Electron (Dual nature of Electron):-
There are two concept about electron:
• Bohr's Concept.
• ‎Debrogile's Concept.

1) Bohr's Concept:-
 According to the Bohr's concept electron is a particle which moves around the nucleus of an atom in circular orbit at a definite distance from the nucleus and its position and momentum both can be calculated.

2) Debrogile's Concept:-
 According to the Debrogile's concept electron is wave particle and has wave motion around the nucleus of an atom.

 "Thus electron has dual nature one particle nature and other wave nature."

Heisenberg's Uncertainty Principle:-
(Given by Heisenberg)

Definition:-
It is impossible to measure the exact position and the momentum of an electron simultaneously.

Explanation:-
According to the Heisenberg's principle, due to dual nature of electron, it is impossible to measure the exact position and momentum of electron at the same time. If momentum of moving electron is measured then its position becomes uncertain and if position of electron is measured suppose by stopping electron at any point then its momentum becomes uncertain.
If uncertainty in momentum of particle (electron) is change in P (momentum)x and uncertainty in position is change in x then according to the Heisenberg's principle product of two uncertainties is equal to Plank's constant which is h.
Thus px. x = h.

Electron Affinity (E.A):-
Change in enthalpy when an electron in the valence shell of an atom to form an anion is called electron affinity. Mostly electron affinity is exothermic.
When an electron is added in the valence shell of an atom then the nucleus of an atom attracts that electron and the electron already present in the atom repel that electron. If the attraction of nucleus on that electron is more than the repulsion of that electrons then energy is released and if the repulsion of electrons is more than the attraction of nucleus then energy is absorbed.
Stability of anion depends on the amount of energy released, if more energy is released then the anion is more stable.
Example
F + 1e ------> F.       H = -342KJ/mol

Cl + 1e ------> Cl.     H = +348 KJ/mol
Thus Cl is more stable than F. Electron affinity of group IIA elements ( Be, Mg, Ca, Sr, Ba), Nitrogen and noble gasses is positive, it means their anions are unstable.
Noble gasses is positive, it means their anions are unstable.
In periodic table E.A decreases in a group form top to bottom and increases in period from left to right.