Chapter 13 : Atomic spectra

موضوع: Chapter 13 : Atomic spectra السبت يناير 12, 2008 2:40 am

1- Bohr's postulates and model of the hydrogen atom:
When an electron jumps from a high level to a lower level, it produces radiation in the form of a photon of frequency n and energy hn, which is equal to the difference between two levels: hn = E₂ - E₁ , E₂ > E₁

2- The line spectrum of hydrogen consists of 5 series. Each line corresponds to a definite energy difference, frequency and wave length.
Leyman UV: (electrons move Down to K ( n = 1) level from higher levels.
Balmer visible: (electrons move down to L (n = 2) level from higher levels.
Paschen IR (infrared) (electrons move down to M (n = 2) level from higher levels.
Bracket IR (infrared) (electrons move down N ( n = 4) level from higher levels.
Pfund far IR (electrons move down to O ( n = 5) level from higher levels.

3- The spectrometer is an apparatus used to decompose light to its components (visible and invisible), to obtain a pure spectrum.

4- X-rays are an invisible em radiation of short wave lengths, first discovered by Rontengen (1895). He called them the unknown (X) rays.

5- X- ray diffraction is used in studying the crystalline structure, and also in the industrial and medical applications.

6- Line spectra:
Is the spectra of elements which have a discrete nature, occurring at wavelengths characteristic of the element. Or It is the spectrum occurring at specified frequencies and not continuously distributed.

7- The emission spectrum: The spectrum resulting from the transfer of excited atoms from a high level to lower level.

8- Continuous spectrum: consists of all wavelengths in a continuous manner.

9- Absorption spectrum: When white light passes through a certain gas, some wavelengths in the continuous spectrum are missing, these wave lengths are the same as those which appear in the emission spectrum of the gas.