As you synthesise new compounds, I wanted to know and understand why is the magic number of chemistry 8? Why do atoms

Question: As you synthesise new compounds, I wanted to know and understand why is the magic number of chemistry 8? Why do atoms with 8 electrons in there outer shell become noble and why do all other atoms try to steal and share their electrons in an attempt to reach 8? Does this mean chemistry should be done on base 8 counting?
- Keywords:
  chemistry,
  subatomic
Asked by Lewis Johns to Aaron on 12 Nov 2014.
- Aaron Acton answered on 12 Nov 2014:
  
  Good question, atoms are happy and least reactive when they are in their lowest energy conformation and as you probably know atoms contain electrons in orbitals that surround the nucleus of the atom. As your teachers have probably taught you there can be 2 electrons in the first orbital shell and a maximum of 8 in the second and 18 in the third.
  
  So atoms can react until they have a full amount of electrons in each ‘shell’ so for example atoms in the first column of the periodic table like Li which has a total of 3 electrons so 2 in the first shell and only 1 in the second shell is reactive. As it only has one electron in the second shell and 7 empty spaces so it wants to lose that 1 electron to form Li+ (which only has 2 electrons).
  
  Whereas, halogen elements like F has a total of 9 electrons so 2 in the first orbital and 7 in the second so it really wants an extra electron to fill up the last orbital and make 8. So it forms F- (which has a total of 10 electrons, 2 in the first and 8 in the second).
  
  The atoms can fit a maximum of 2 and 8 electrons in the first and second shells due to the size of the electrons and charge repulsions between the electrons. Any more and its too crowded so they cant all fit and the electrons repel each other as they are negatively charged.
  
  Things do get slightly more complicated as the orbitals that contain 8 electrons actually are made up of a combination of different orbitals called S and P orbitals S orbitals contain 2 electrons and P orbitals contain 6 giving a total number of 8. I think this may be going into a bit too much detail but you will learn more of this if you choose A-level chemistry 😉
  
  But the rule of 8 is only a very rough guide!