1. 3.5 Energy levels and spectra

2. 3.5 Energy levels and spectra
DISPERSION

3. 3.5 Energy levels and spectra
DISPERSION
White light (from the
sun or a lamp) is made
up of different colours.
Raindrops or glass will
separate these colours
into a continuous spectrum
from about 400nm to 650nm.
This is called dispersion.

5. Line spectra discrete: coloured lines due to photons of certain energies only

6. Using a tube of glowing gas produces a line spectrum of discrete colours
whose wavelengths are unique to the element’s excited atoms’ energy levels .

7. Using a tube of glowing gas produces a line spectrum of discrete colours
whose wavelengths are unique to the element’s excited atoms’ energy levels .
The photons producing each line all have the same energy.

8. Energy of emitted photon = hf = E1- E2
Using a tube of glowing gas produces a line spectrum of discrete colours
whose wavelengths are unique to the element’s excited atoms’ energy levels .
The photons producing each line all have the same energy.
Each photon is emitted when an atom de-excites from a higher energy level
to a lower energy level.
Energy of emitted photon = hf = E1- E2

9. Band spectra: a fine structure is produced by the energies of chemical bonds in the molecules
Continuous spectra:
Continuous spread of wavelengths due to a continuous spread of photon energies

10. Band spectra: a fine structure is produced by the energies of chemical bonds in the molecules
Continuous spectra:
Continuous spread of wavelengths due to a continuous spread of photon energies

11. Band spectra: a fine structure is produced by the energies of chemical bonds in the molecules
Continuous spectra:
Continuous spread of wavelengths due to a continuous spread of photon energies

12. Band spectra: a fine structure is produced by the energies of chemical bonds in the molecules
Continuous spectra:
Continuous spread of wavelengths due to a continuous spread of photon energies

13. In the solar spectrum there is strong absorption at wavelengths corresponding
to the emission spectra of hydrogen and helium
This shows the presence of these elements in the hot gas around the sun.

14. E = 13.6 eV
E = 0 eV

15. E = 13.6 eV
E = 0 eV

16. visible
E = 13.6 eV
E = 0 eV

17. visible ir
E = 13.6 eV uv
E = 0 eV

18. visible ir
E = 13.6 eV
Energy of an emitted photon
= _ x 13.6eV
n n12 uv
E = 0 eV

19. Energy of emitted photon = hf = E1- E2

20. Energy of emitted photon = hf = E1- E2

21. Energy of emitted photon = hf = E1- E2

22. Energy of emitted photon = hf = E1- E2

23. Energy of emitted photon = hf = E1- E2