The Arrangement of Electrons in Atoms

Although the nucleus of an atom contain the heavier sub-atomic particles (Protons and Neutrons), there is also another major sub-atomic particle. - ELECTRONS

Electrons

• From far distances away (relative to their size), electrons move around the nucleus
• They travel very quickly in electron energy levels
  • Very much like how the planets orbit the sun
• The exact position of an electron in an energy level cannot be said

Energy Levels (electron shells)

• Electrons only occupy certain, definite energy levels
• Electrons cannot exist BETWEEN energy levels
• Each energy level can only hold a certain number of electrons
  • First energy level - up to 2 electrons
  • Second energy level - up to 8 electrons
  • Third energy level - up to 18 electrons
    • Fourth energy level - up to 32 electrons
    • Fifth energy level - up to 50 electrons
    • Sxth energy level - up to 72 electrons
    • This.. we don't really need to know.
    • Energy levels are called K, L, M, N, O, P
      • K- 1st - 2 electrons
      • L- 2nd - 8 electrons
      • M- 3rd - 18 electrons
      • N- 4th - 32 electrons
      • O- 5th - 50 electrons
      • P- 6th - 72 electrons
    • Some energy levels reach a certain stability even when the number of electrons that has occupied that level is not the maximum number of electrons that can be occupied.
    • This whole 'super indented' bit is extra and it is not necessary to know this.

'The third energy level can be occupied by a maximum of 18 electrons'

from page 36 IGCSE Chemistry Second Edition

• When the maximum number of electrons a level can hold have occupied that level, the atom reaches a certain stability.
  • The next electrons go into the next energy level
• **Energy level three is a little 'special'
  • When it is occupied by 8 electrons, a certain stability is given to the atom and the next 2 electrons go into the FOURTH energy level.
  • However, after that, the there cannot be a 2,8,8,3 because after the 2 electrons occupy the fourth level, the next 10 electrons go back to the third energy level and fill up the remaining spaces.**
  • Electrons fill energy levels starting form the one nearest to the nucleus
  • The energy level nearest to the nucleus has the least energy

Atomic Structure and Periodic Table

links to other subtopics in this section can be found here.

Chemistry-IGCSE