atoms molecule nuclei grade 12

1. Atoms , molecules & nuclei
By Prof. Smt Sanchita Jadhav Yadav
Prof. Mr .Vipinkumar Yadav

2. Geiger – Marsden Experiment

3. Rutherford’s Model of Atom

4. Bohr’s Theory of Hydrogen Atom
Postulate 1:
The electron in a hydrogen
atom revolves in circular orbit
around the nucleus with nucleus
as the centre of the orbit.
The necessary centripetal force
for circular motion is provided by
electrostatic force of attraction
between the positively charged
nucleus & negatively charged
electron.

5. Postulate 2:
The electron
revolves round the
nucleus only in those
orbits for which the
angular momentum
is equal to an integral
multiple of h/2π ,
where h is planck’s
constant.

6. Postulate 3:
when electrons
jumps from orbit of
higher energy to an
orbit of lower energy,
it radiates energy in
the form of photon.

7. Hydrogen spectrum

8. 1.Lyman series:
This series arises due to transitions of electrons from
different outer orbits to the first Bohr’s orbit (p = 1).
Therefore the wavelength for Lyman series is given by
n = 2,3,4……
For n = 2 & 3 , the wave lengths are 1216 AU & 1025 AU
respectively i.e this series lies in the ultra violet region of
electromagnetic spectrum.

9. 2.Balmer series:
This series arises due to transitions of electrons from
different outer orbits to the second Bohr’s orbit (p = 2).
Therefore the wavelength for Balmer series is given by
n = 3,4……
For n = 3 & 4 , the wave lengths are 6563 AU & 4868 AU
respectively i.e this series lies in visible region of
electromagnetic spectrum.

10. 3.Paschen series:
This series arises due to transitions of electrons from
different outer orbits to the third Bohr’s orbit (p = 3).
Therefore the wavelength for Paschen series is given by
n = 4,5,6,7……
For n = 4 & 5 , the wavelengths are 18750 AU & 12820 AU
respectively i.e this series lies in infrared region of
electromagnetic spectrum.

11. 4.Brackett series:
This series arises due to transitions of electrons from
different outer orbits to the fourth Bohr’s orbit (p = 4).
Therefore the wavelength for Brackett series is given by
n = 5,6,7……
For n = 5 & 6 , the wavelengths are 40518 AU & 26253 AU
respectively i.e this series lies near infrared region of
electromagnetic spectrum.

12. 5.Pfund series:
This series arises due to transitions of electrons from
different outer orbits to the fifth Bohr’s orbit (p = 5).
Therefore the wavelength for Pfund series is given by
n = 6,7……
For n = 6 & 7 , the wavelengths are 75587 AU & 46533 AU
respectively i.e this series lies far infrared region of
electromagnetic spectrum.

13. Energy level diagram for hydrogen
atom