SPECTRAL LINE FORMATION AND ATOMS

To understand spectral lines you have to understand some Atomic Physics.

• What makes an element?

  The number of protons in the nucleus of an atom is what defines an atom.

• For example: Hydrogen (H) atoms have 1 proton ( )
  • H with  and 1 electron ( )  is ``neutral'' hydrogen ( ).
  • H with  and  and a neutron ( ) is a ``heavy'' of Hydrogen called deuterium ( ).
  • If a is added to Hydrogen, we then have a different element - Helium ( ).

  

  Q.) How many neutrons in ?

  

• What does this have to do with light and spectral lines? Lots of clever experiments around the turn of the century demonstrated that:
  1. light can be thought of as a stream of ``quanta'' called photons. Each photon carries an energy (h is ``Planck's constant'', is the frequency).

  2. Atoms had a crazy structure in which only certain orbits were allowed for the electrons - that word again, the orbits are ``quantized''.

  

• ``g'' = ``ground'' state = lowest energy configuration

• ``1'' = 1st excited state = higher energy configuration

• ``2'' = 2nd excited state = higher energy yet

• etc. right on up to where the electron is no longer bound to the atom.