Chemistry - Key definitions and formulas

Key terms for OCR exam board

HideShow resource information




  • N= VC /1000
  • C= 1000N/V
  • N=m/Mr
  • m=N/Mr
1 of 3


  • Relative atomic mass ; This is the mass of an atom compared to 1/12 of the mass of an atom of carbon 12. Where carbon is exactly 12.
  • Relative isotopic mass ; The mass of an isotope compared to 1/12 the mass of a carbon 12 atom, where carbon is exactly 12.
  • Relative formula mass ; The mass of a compound compared to 1/12 the mass of a carbon 12 atom, where carbon is exactly 12.
  • The mole is a unit of measurement used in chemistry to allow us to weigh out the correct number of particles, (ions, electrons, compounds etc ... for a chemiscal reaction)
  • Ionisation energy ; Is the energy required to remove 1 mole of electrons from1 mole of gaseous atoms to form 1 mole of gaseous ions.
  • Periodicity ; A graph has this when a repeated pattern is apparent... E.g... First Ionisation energies.
  • Electron ; Cloud of negative charge, it fills a volume in space called an orbital.
  • Orbital ; A space of volume
2 of 3

Explaining Electrons

The electon configuration is now using S,P,D and F's...

  • E.g Hydrogen would be 1s1... :)
  • So it goes up like... :
  • 1s2, 2s2, 2p6,3s2,3p6,4s2,3d10,4p6...
  • The 4s2 gets filled before the 3d10 because it is easier to fill the 4s2.... after the 4th s - orbital is completed, it goes back to filling up the 3d- orbital
3 of 3



Very helpful, thanks :)

Similar Chemistry resources:

See all Chemistry resources »See all Calculations resources »