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Atomic Physics II. Hydrogen Atom Model. Thomson Model. - PowerPoint PPT Presentation
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Plumb Pudding Model (1897)- Joseph John Thomson proposed that the atom was a sphere of positive electricity (which was diffuse) with negative particles imbedded throughout after discovering the electron, a discovery for which he was awarded the Nobel Prize in physics in 1906.
Thomson Model
http://www.chem.rochester.edu/~chem131/wkshp/rutherford.mov
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Total Energy of the electron in the hydrogen atom
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Energy Levels on hydrogen atom
Rydberg constant and Atomic spectrum
The frequency of the radiant energy is Eh
where h is the Plank constant.
22
21
212
12
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11
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.
In particular if n1 = 2 n2 = 3, 4, 5, ....... this series is known as Balmer series.
Other series : n1 = 1 n2 = 2, 3, 4, ....... Lyman
n1 = 2 n2 = 3, 4, 5, ....... Balmer
n1 = 3 n2 = 4, 5, 6, ....... Paaschen
n1 = 4 n2 = 5, 6, 7, ....... Brackett
n1 = 5 n2 = 6, 7, 8, ....... Pfund
(n2 = ) of Paschen series with n2 > 3 and n1 = 3
and the corresponding energy.
Example 4.1
Calculate the limiting value
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4.31 Emission spectra
Line spectra
- separate bright lines with definite wavelength- produced by luminous gases at low pressure in the discharge tube- the atoms are far apart not to interact with each other- no 2 elements give the same spectrum
Band spectra
Spectrum produced by molecules or molecular vapour
- several well defined groups / bands of lines- closed together- obtained from molecules of glowing gases heated / excited at low pressure- arise from the interaction % atoms in each molecules e.g. blue inner cone of a Bunsen burner flame
Continuous spectra
-emitted by hot solid and liquid also by hot gases at high pressure
-atoms are so closed that interaction is inevitable
- all wavelengths are emitted
The Absorption Spectra
-line, band, continuous spectra are again obtained
- when white light passes through a cooler gas or vapour, the atom absorb the light of the wavelengths which they can emit and then re- radiate the same wavelengths almost at once but in all directions
- dark lines occur against the continuous spectrum of white light exactly at those wavelengths which are present in the line emission spectrum of the gas or vapour e.g. absorption spectrum of iodine vapour
Sun’s spectrum & the Fraunhofer dark lines
prescence of a layer of cooler gas round the sunabsorption spectrum
http://tycho.bgsu.edu/~laird/phys655/class/IC.html