1. atomic excitation and ionisation
…a mad scientist’s guide…

2. …so what do we need to know...?
about quantisation of electron orbitals
about energy levels
how excitation & ionisation work
what a line spectrum is

3. …so what do we need to know...?
how to calculate the frequencies of the photons emitted by transitions
how to convert between electron-volts
and Joules

4. …electron orbitals and quantum numbers…
Keywords:
Quantum number
Energy Level
Ground State

5. …electron orbitals and quantum numbers…
Keywords:
Excited State

6. …collisions (or absorption of a photon) can lead to excitation…
…and then subsequent relaxation leads to the emission of a photon.

7. …energy levels…
Because the energy levels are quantised the emitted photons will be discrete frequencies. The frequency is determined by the formula:

8. …line spectra…
…the emitted photons are at discrete wavelengths, corresponding to the transitions…

9. …so let’s try an example…
Consider…
…an excited hydrogen atom with quantum number n=4 relaxes to the ground state (n=1). What will be the wavelength of the emitted photon…?

10. …so let’s try an example…
So we start with electron in the excited state n=4
and we finish back in the ground state n=1

11. …so the energy of the emitted photon is…
∆E = –0.85 eV –(–13.6 eV)
= eV
= (12.75 eV)•(1.6x10-19 Joules/eV)
= 2.04x10-18 Joules

12. …and so…
…we use the formula
…and find…
(…or 97.5 nm or 975Å or…)

13. …you should also know…
…how to find de Broglie wavelengths…

14. …so a quick recap…
ground state – when the electron is in its lowest orbital, with quantum number n=1
excitation – when an electron is ‘kicked’ into a higher orbital by a collision
relaxation – when the electron
drops down to a lower energy
level, or back to ground state

15. …so a quick recap…
ionisation – when an atom completely loses an electron due to a collision
energy level – the energy associated with the quantum state of the atom
line spectrum – a graph showing
the wavelength or frequency of
the emitted photons

16. …so a quick recap…
electron-volt (eV) – a more practical unit of energy for working on these scales.
- to convert Joules to eV we just
multiply by the electronic charge
- to convert eV to Joules we just
divide by the electronic charge

17. …different approaches to the questions…
determine transition from wavelength of emitted radiation
determine transition and values of energy levels from energy of emitted radiation
find ionisation energy
find e.g. longest wavelength

18. …different approaches to the questions…
determine all frequencies of radiation that could be emitted given collision energy
label transitions on diagram
calculate de Broglie Wavelength of incident particles
…and lots of wordy ones…

19. …so now it’s your turn… …you’ll need some formulae…
…and some constants
…so that’s it!
enjoy…!!! 