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

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

…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

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

…electron orbitals and quantum numbers… Keywords: Excited State

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

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

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

…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…?

…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

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

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

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

…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

…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

…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

…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

…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…

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