Topic 1 - emission spectra Flashcards
light travels in photons
equation
each photon has its own discrete energy value which depends upon its frequency
E = hf
h = planks constant h = 6.63 x 10-34 js
Energy levels
electrons exist in shells around the nucleus
ground states
the 1st shell is called the ground state
the other shells are called exited levels
energy level facts
electrons only exist in discrete energy levels
electrons in the shell nearest the nucleus will have the least amount of energy
electrons in shells further out will have more energy
if an electron gets some extra energy it can jump up to the next energy level and we say it is an exited state
why are the energies getting bigger in a - direction as you head nearer the ground state
0 j is the point of ionisation (where the electron will finallt leave the atom)
excitation in genral
if electrons gain enough energy they will get really exited. if they get exited enough they ill jump to the next level
the amount of energy they need to jump an energy level is a quantised amount, it is different for every energy level and every different atom
if they don’t get the exact amount they won’t jump so they need particular frequencies
it can happen 2 ways
excitation by electron collision
an electron that is moving will have a particular kinetic energy
if this energy is the right amount it collides with an atom, it can transfer this kinetic energy
excitation by photon absorption
an electron can also jump to a higher energy level (if there is a gap) by absorbing a photon
again the energy must be exact
if the energy is high enough, it might even be able to jump 2 energy levels
de - excitation
electrons cannot stay in an exited state for very long. they like to be in the lowest possible energy level (ground state) and will go there if they are left alone
each time an electron falls to a lower energy level it loses energy. this energy is radiated as a photon of frequency ‘f’
E1 - E2 = △E = hf
where we get spectra lines from
every time electrons fall back down to a lower energy level, the energy that it loses is emitted as a photon
each energy level jump will produce a single photon. so an electron falling from the 2nd sate back to the ground state will emit 2 separate photons, each with different energies (as the amount of energy between each level is different
what can be shown on the emission spectra
if they electrons jump down an energy level they only emit photons of a certain energy - hence frequencies - which can be shown on an emission spectrum.
explain how the diffraction grating produces an emission spectra
light contains many wavelength
so light is diffracted in all directions when it leaves the grating
if phase difference half wavelength the the waves that meet will cancel out so destructive interference
if the phase difference is a wavelength the waves add up constructive interference
