9. Energy Levels in Atoms

- The electron volt is the kinetic energy carried by an electron after being accelerated at rest through a PD of 1 volt.

- Therefore 1eV = 1.6x10^-19J

- Electrons in atoms can only exsist at pre-defined levels. They can move to higher levels by gaing photons of energy, and move lower by emitting photons.

- The energy of the photons is the same as the difference between the energy at two levels.

Change in E = E1 - E2 = hf = hc/l

- When an electron is removed from the atom it is ionised. The ionisation energy is the amount needed to remove it from ground state (n=1)

- Flourscent tubes use this excitation and emission for visible light.

- They contain mercury vapour which a high voltage is put across, this accelerates the free electrons which ionises some of the mercury atoms producing more. When the free electrons collide with the mercury electrons, the mercury electrons are excited. They then de-excite and loose energy by emitting photons in the UV range. The phospurus coating then absorps these photons exciting it's electrons which then cascade down and de-excite, emitting lower photon energies of visible light.

- If you split the light emitted by a prism or diffraction grating a line emission spectra is produced as a series of lines, where each corresponds to a particular wavelength.

- Line spectra provide evidence that electrons can only exsist in pre-set energy levels, since only…