1. Original slide prepared for the Electrons in atoms. As atoms are neutral the number of electrons is given by the atomic number.

2. Original slide prepared for the Electron shells Electrons orbit the nucleus in shells. The first shell, the one nearest the nucleus, can only have two electrons. The next shell can have 8. The third shell 18. (Although it can be partially full with 8). The lower shells must be filled first before electrons can be put into the upper shells.

3. Original slide prepared for the carbon atom C 6 atomic number so six electrons X X X 2, 4 XX X X X X

4. Original slide prepared for the lithium atom Li 3 atomic number so three electrons X X X 2, 1 XX X

5. Original slide prepared for the sodium atom Na 11 atomic number so eleven electrons X X X X X 2, 8, 1 X XX X X X X X X X X X

6. Original slide prepared for the calcium atom Ca 20 atomic number so twenty electrons X X X X X 2, 8, 2, 2 X X X X X XX X X X X X X X X X XX X X X XX XX

7. Original slide prepared for the calcium ion 20 atomic number positive ion X X X X X 2, 8 XX X X X X X X X X Ca 2+ so 20-2 electrons = 18 [ ] 2+ X X X X X X XX XX X X X X XX

8. Original slide prepared for the [ ] magnesium ion 12 atomic number positive ion X X X X X 2, 8 XX X X X X X X X X Mg 2+ so 12-2 electrons = 10 2+

9. Original slide prepared for the chloride ion 17 atomic number negative ion X X X X X 2, 8 XX X X X X X X X X X X X X X X X X X X X X X X XX Cl - - so 17+1 electrons = 18 [ ] -

10. Original slide prepared for the oxide ion 8 atomic number negative ion X X X X X 2, 8 O 2-2- 2- so 8+2 electrons = 10 [ ] 2-2- X X X X X X X X XX

11. Original slide prepared for the electron shells (atom)

12. Original slide prepared for the electron shells (ion)

13. Original slide prepared for the References Steve Lewis for the Royal Society of Chemistry