Bohr showed that the energy levels were proportional to 1/n

When an electron falls from one energy level E

Where n

The term me

Putting n

Therefore:

n

n

n

Every electron within an atom is described by four numbers called quantum numbers:

(a) the principal quantum number (n), representing the energy level

(b) the orbital quantum number (L), which may have any integral value between 0 and n -1

(c) the magnetic quantum number (m), which may have any integral value between - L and + L

(NB it is normal to write the orbital quantum number as l but we are using L to make it clearly different from 1.)

(d) the spin quantum number (s), which may have values of + ½ or ½ .

Related to these quantum numbers is the

This important statement may be used to predict the numbers of electrons in the shells of an atom.

Lets think about the K-shell and L-shell.

(a) In the K-shell, n = 1. The only possible values for L and m are 0, s can be + ½ or ½, and so only two electrons can exist in this shell.

(b) In the L-shell, n = 2. In this shell eight electrons are possible, as shown by the following table:

n | L | m | s | n | L | m | s | |

2 | 0 | 0 | + ½ | 2 | 0 | 0 | ½ | |

2 | 1 | -1 | + ½ | 2 | 1 | -1 | ½ | |

2 | 1 | 0 | + ½ | 2 | 1 | 0 | ½ | |

2 | 1 | +1 | + ½ | 2 | 1 | +1 | ½ |

One result of this principle is that you can never squeeze two particles together to such an extent that they occupy the same state - objects must have a finite volume! It also means that if the exclusion principle did not apply then all electrons in an atom would end up in the lowest possible energy state. Chemistry would be changed forever and the world as we know it would not exist.