Notes on Atomic Physics
The hydrogen atom was initially viewed as an electron orbiting
a proton. However based on electomagnetic theory this model is not practical
because the atom would have an extremely short life.
Bohr proposed a model of a hydrogen atom in which the electron has a number of stable
orbits with set angular momentum in multiples of h / (2.p ).
i.e. electrons can only occupy orbits with angular momentum of n. h / (2.p )....
r n = n 2 r 1 n = 1, 2, 3...Energy Levels
Note : 1 eV (Electronvolt = 1,6 x 10-19 Joules
E n = E 1 / n 2 n = 1, 2, 3... .... ( E 1 = -13.6 eV = -2.18 x 10-18 J.)
These permitted energies
of an atom are called energy levels. The energy levels are all negative and as a result
the electron does not have enough energy to escape from the atom. As n increases En
approaches 0 , at this level the electron is no longer bound to the proton and the atom ceases to
exist. The work input to remove an electron from an atom in its ground state is
called the ionization energy; for hydrogen the ionization energy is 13.6 eV.
When a gas or vapor is excited by the passage of an electric current, light is given off is certain
specific wavelengths. Each element has characteristic emission line spectrum.
The wavelengths in this spectrum fall into fixed series with member wavelengths related by simple formula.
E initial - Efinal = h . fQuantum Theory of The Atom
In the Bohr model of the atom one quantum number is needed, in the quantum theory four quantum numbers are used.
This theory works for atoms with numerous electrons as well as for the hydrogen atom. The quantum numbers are identified below
The energy levels possible are mainly determined by n and only to a low extent by l and m l.
For the hydrogen atom the energy levels are the same as for the Bohr atom.
Every electron behaves as though it is a spinning charge sphere. The amount of spin
is fixed but there are two possible directions that the angular momentum vector
can point in the magnetic field : "up" (ms= + 1 / 2) and "down" (ms= - 1 / 2).
if n = 3 then l = 0, 1, 2
The maximum number of electrons in the M (n= 3)shell are 18Additional Information.
Sites & Links For Atomic Physics