Electron Shells

Electron Shells

1. Electron shell rules

   • Electrons always occupy shells
   • The lowest shells 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, 2nd shell 8, 3rd shell 8
   • 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 and this makes the atom want to react to fill it

2. Working out electronic structures

   • Nitrogen
     • The periodic table tells us that nitrogen has seven protons so it must have seven electrons. The first shell can only take 2 electrons and the second shell can have a maximum of 8 electrons. The electronic structure must be 2,5
   • Argon
     • The periodic table tells us that argon has eighteen protons so it must have eighteen electrons. The first shell can only take 2 electrons and the second shell can have a maximum of 8 electrons, the third shell also has a maximum of 8 electrons The electronic structure must be 2,8,8
   • Sodium
     • The periodic table tells us that sodium has eleven protons so it must have eleven electrons. The first shell can only take 2 electrons and the second shell can have a maximum of 8 electrons, the third shell also has a maximum of 8 electrons. The electronic structure must be 2,8,1
   • Phosphorus
     • The periodic table tells us that phosphorus has 15 protons so it must have 15 electrons. The first shell can only take 2 electrons and the second shell can have a maximum of 8 electrons, the third shell also has a maximum of 8 electrons. The electronic structure must be 2,8,5