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CBSE NOTES CLASS 12 PHYSICS

CHAPTER 12 ATOMS

Dalton’s atomic theory

Thomson’s atomic model

Limitations of Thomson’s atomic model

Rutherford’s atomic model

Scattering of alpha particles

Electrostatic force between the nucleus and α–particle

Distance of closest approach

Impact parameter

Rutherford’s scattering formula

Limitations of Rutherford atomic model

Bohr’s atomic model

Radius of orbit of electron

Velocity of electron in an orbit

Frequency of electron

Time period of revolution of an electron

Kinetic energy of an electron revolving in an orbit

Potential energy of an electron in an orbit

Total energy of an electron in an orbit

Wave number of an electron in an orbit

Quantum numbers

Hydrogen spectrum series

Lyman series

Balmer series

Paschen series

Brackett series

Pfund series

Line spectra and electron transitions between energy levels

de Broglie’s explanation of Bohr’s second postulate of quantisation

Limitations of Bohr’s atomic model

CBSE NOTES CLASS 12 PHYSICS

CHAPTER 12 ATOMS

Hydrogen spectrum series

Each element emits a spectrum of radiation, which is characteristic of the element itself. The spectrum consists of a set of isolated parallel lines and is called the line spectrum.

Hydrogen spectrum contains five series

Lyman Series - When electron jumps from n = 2, 3, 4, … to n = 1 orbit, a line of Lyman series is obtained. This series lies in ultra violet region.

Balmer Series - When electron jumps from n = 3, 4, 5,… to n = 2 orbit, a line of Balmer series is obtained. This series lies in visual region.

Paschen Series -When electron jumps from n = 4, 5, 6,… to n = 3 orbit, a line of Paschen series is obtained. This series lies in infrared region.

Brackett Series -When electron jumps from n = 5,6, 7…. to n = 4 orbit, a line of Brackett series is obtained. This series lies in infrared region.

Pfund Series -When electron jumps from n = 6,7,8, … to n = 5 orbit, a line of Pfund series is obtained. This series lies in infrared region.

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Emission lines in the spectrum of hydrogen

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