Arrangement of Sub-atomic Particles

• Electron shells


  • an atom has one or more electron shells
  • the first electron shells is the lowest energy level and is closest to the nucleus. Electrons occupy the inner shells with the lowest energy first, the first electron shell can have at most 2 electrons
  • the valence electron shell is the highest energy level and is furthest from the nucleus, electrons found in the valence electron shell are valence electrons
• Valence Shells


  • atoms with fully filled valence Shells are unreactive and stable (noble gases)
  • atoms with valence shells that are not fully filled are reactive, and tend to gain or lose or share electrons to achieve a stable electronic configuration