1. Electronic structure and the periodic table

2. Properties of the nucleus and electrons

3. How are electrons arranged?
Electrons are not evenly spread but exist in layers called shells.
The arrangement of electrons in these shells is often called the electron configuration.
1st shell
2nd shell
3rd shell

4. How many electrons per shell?
Each shell has a maximum number of electrons that it can hold. Electrons will fill the shells nearest the nucleus first.
1st shell holds a maximum of 2 electrons
2nd shell holds a maximum of 8 electrons
3rd shell holds a maximum of 8 electrons

5. Calculating electron configurations

6. Summary: the atom so far
The nucleus is:
Dense – it contains nearly all the mass of the atom in a tiny space.
Made up of protons and neutrons.
Positively charged because of the protons.
Electrons are:
Thinly spread around the outside of the atom.
Very small and light.
Negatively charged.
Found orbiting the nucleus in layers called shells.
Able to be lost or gained in chemical reactions.

7. Which element am I?

8. I am made up of 7 electrons.

9. Answer: Nitrogen

10. I am made up of 12 electrons

11. Answer: Magnesium

12. I have 2 electrons in my first shell and 3 electrons in my second shell.

13. Answer: I am Boron

14. I have 2 electrons in my first shell, 8 in my second shell and 7 in my third shell.

15. Answer: I am Chlorine

16. I have two shells. In my second shell I have 6 electrons.

17. I am oxygen

18. I have 3 shells. In my outer shell I have 3 electrons.

19. Answer: I am Aluminium

20. Electron shells
Electrons are arranged in shells around an atom’s nucleus.
Each shell has a maximum number of electrons that it can hold. Electrons will fill the shells nearest the nucleus first.
2nd shell holds a maximum of 8 electrons
1st shell holds a maximum of 2 electrons
3rd shell holds a maximum of 8 electrons
This electron arrangement is written as 2,8,8

21. What’s the electron arrangement?