Electron Shells

Electron Shells

1. Electron shell rules

   • Electrons always occupy shells(sometimes called energy levels)
   • The lowest energy levels are always filled first
     • These are the ones closest to the nucleus
   • Only a certain number of electrons are allowed in each shell
     • 1st shell
       • 2 electrons
     • 2nd shell
       • 8 electrons
     • 3rd shell
       • 8 electrons
   • Atoms are much happier when they have full electron shells
     • Like the noble gases in group 0
   • in most atoms the outer shell is not full
     • This makes the atom want to react to fill it

2. Working out electronic structure

   • 1. Nitrogen has 7 protons so it must have 7 electrons
     • 2. The first shell can only hold 2 electrons and the second shell can hold a maximum of 8 electrons
       • 3. So the electronic structure for nitrogen must be 2,5
   • 1. Argon has 18 protons so it must have 18 electrons
     • 2. first shell must have 2 electrons, the second shell must have 8 electrons and so must the third
       • so the electronic structure for argon is 2,8,8
   • The structure must add up to what the protons and electrons are