Energy levels in hydrogen
If
an electron from a low level is given energy it will be raised to a higher, or excited, level. This can
be done electrically, by heat, by collision with another atom, by radiation or by a free electron hitting
the atom. However the electron in the atom will only be excited if the energy of the incoming
quantum of energy in whatever form is exactly the same as the difference in energy between the
two levels.
When an electron falls from one level to another energy is emitted in the form
of a quantum of radiation. The energy of this quantum and therefore its frequency and wavelength
is determined by the difference in energy between the two levels.
Example problem
Calculate the frequency and wavelength of a quantum of radiation emitted when an electron in level 4 falls to level 2.
Using the data in the table on page:
Energy of level 4 = - 1.36 x 10-19 J
Energy of level 2 = - 5.42 x 10-19 J
Energy difference (E) = + 4.06 x 10-19 J
Therefore frequency = E/h = 4.06 x 10-34/6.63 x 10-34 = 6.12 x 1014
Wavelength = c/f = 3 x 108/6.12 x 1014
= 4.9 x 10-7 m = 490 nm
This is in the deep blue to violet end of the visible spectrum.
N.B notice that joules have been used and not electron volts.
schoolphysics: Emission of radiation animation
To see an animation of the emission of radiation from an atom click on the animation link.
A VERSION IN WORD IS AVAILABLE ON THE SCHOOLPHYSICS USB
