2. hydrogen atom 1 atomic number so one electron 1 H X

3. helium atom 2 atomic number so two electrons 2 He XX

4. lithium atom 3 atomic number so three electrons 2, 1 Li X XX

5. beryllium atom 4 atomic number so four electrons 2, 2 Be XX XX

6. boron atom 5 atomic number so five electrons 2, 3 B XX XX X

7. carbon atom 6 atomic number so six electrons 2, 4 C XX XX XX

8. nitrogen atom 7 atomic number so seven electrons 2, 5 N XX XX XX X

9. oxygen atom 8 atomic number so eight electrons 2, 6 O XX XX XX XX

10. fluorine atom 9 atomic number so nine electrons 2, 7 F XX XX XX XX X

11. neon atom 10 atomic number so ten electrons 2, 8 Ne XX XX X X XX X X

12. sodium atom 11 atomic number so eleven electrons 2, 1, 8 Na X XX XX XX XX XX

13. magnesium atom 12 atomic number so twelve electrons 2, 2, 8 Mg XX XX XX XX XX XX

14. aluminium atom 13 atomic number so thirteen electrons 2, 3, 8 Al XX XX XX XX XX XX X

15. silicon atom 14 atomic number so fourteen electrons 2, 4, 8 Si XX XX XX XX XX XX XX

16. phosphorus atom 15 atomic number so fifteen electrons 2, 5, 8 P XX XX XX XX XX XX XX X

17. sulphur atom 16 atomic number so sixteen electrons 2, 6, 8 S XX XX XX XX XX XX XX XX

18. chlorine atom 17 atomic number so seventeen electrons 2, 7, 8 Cl XX XX XX XX XX XX XX XX X

19. argon atom 18 atomic number so eighteen electrons 2, 8 Ar XX XX XX XX XX XX XX XX XX

20. potassium atom 19 atomic number so nineteen electrons 2, 8 K XX XX XX XX XX XX XX XX XX, 1, 1 X

21. calcium atom 20 atomic number so twenty electrons 2, 8 Ca XX XX XX XX XX XX XX XX XX, 2, 2 XX