ChemistsOnline*

 ionisation energy down a group , usually decreases due:

  • more electrons as you go down the group are added to the atoms 
  • more shells created 
  • causing the outer shells to have more shielding from the nucleus
  • less attraction towards the nucleus, therefore its easier to remove them 

ionisation energy increases across a period 

  •  because as you go across the period number of protons increase
  • stronger positive charge in the nucleus 
  • more attraction is created between the nucleus and the electrons 
  • more energy is needed to remove the outer shell electrons 
  1. between Mg and Al, ionisation energy decreases 
  2. the outer electron of Al is found in a 3p orbital 
  3. which has a higher energy than the 3s orbital 
  4. less energy will be needed to remove the electron 
  • between the ie of p and ie of s  there is a drop
  • in the 3p orbital of p it will be very stable because there is only one electron in each 
  •  in the 3p orbital of s , one of the orbitals has 2 electrons 
  • the two paired electrons repel more making it easier to remove it with less ionasation energy

atomic radius  

increase down the group because

  •  number of electrons increase so size increases 
  • more shells are filled 
  • one extra main level is now in place 

decreases across the period

  •  one more proton is added in the nucleus and one more electron is added in the outer shell
  • the charge in the nucleus increases and there is more attraction between the electrons and in the nucleus 

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