Energy levels and photon emission

what do electrons naturally occupy?

the lowest energy levels available, under these conditions the atom and its electrons are said to be in ground state.

what is an excited state?

when an electron absorbs a photon with enough energy to raise it to a higher energy level, this makes the atom unstable so after a short time the electron will de-excite.

what is a de-excited state?

when an electron loses energy by emitting a photon, so it can return to a lower energy level.

on an energy level what does photon absorbtion look like?

upward transition.

on an energy level diagram what does photon emission look like?

downward transition.

in relation to energy levels what is the energy of a photon given by?

hf= E2-E1 ,where E1=energy level of higher level and E2= energy level of lower energy level.

if there is a relation between speed of light, frequency, wavelength and energy levels, the wavelength of the emitted radiation is given by:

wavelength=hc/E2-E1

how can a line spectrum be created?

by passing a current through an ionised gas.

how are emission spectra created?

use an excited gas, the electrons in the excited atoms will de-excite, and photons will be emitted, pass the emitted light through a prism or difraction grating.

what does an emission spectrum look like?

Coloured lines on a black background

with regards to line spectra, how can elements be identified?

each element has a unique emission and absorbtion spectrum, we can use these to identify them.

what does each line in an emission spectrum correspond to?

a wavelength of light.

in regards to line spectra, what is the equation that links wavelength, and change in energy?

change in energy level= hc/wavelength

how are absorption spectra created?

when white light passes through a low pressure gas, some electrons absorb energy and are excited, the wavelengths of light they absorb corresponds exactly to the energy needed to make that particular upwards transition. when these electrons de-excite, photons are emitted in all directions rather than the original direction of white light. thus some wavelengths appear to be missing.

what does an absorption spectrum look like?

Black lines on a coloured background

for the same element, how are the absorption and emission spectra related?

they are the inverse of eachother.

what does the equation wavelength=hc/E2-E1 show?

the larger the change in energy level, the shorter the wavelength.

what is ionisation?

when a photon or another free electron gives an electron too much energy for it to go to the next energy level or the one after it and instead it completely leaves the atom, we are left with a free electron and an ion.

what is one eV equal to in joules?

1.6*10^-19

How do fluorescent tubes work?

• high voltage applied across the tube, electrons flow from cathode to anode producing an elctron beam

• beam electrons collide with electrons in mercury atoms transferring Ek in collision.

• atomic elctrons in mercury atoms are excited and move to higher energy level

• high energy level state is unstable so the electrons de-excite

• as they de-excite the lectrons release that energy by emitting photons in the UV range of wavelengths.

• the UV photons the collide with atoms of the phosphor coating and excite them into a higher energy level.

• as phosphor elctrons de-excite, they do so in stages of emitting photons in the visible light range of wavelengths.