Question

How can I learn valencies of the first 20 elements?

Answer 1

Hint:The number of valence electrons present in an atom or element can be determined by using the position of the element in the periodic table. For example nitrogen belongs to group 15 and it has 5 valence electrons.

Complete step-by-step answer:- In the question it is asked how we can learn the valencies of the first 20 elements in the periodic table.
- First we should have the first 20 elements which are present in the periodic table.
- The first 20 elements are as follows.
1. Hydrogen, 2. Helium, 3. Lithium, 4. Beryllium, 5. Boron, 6. Carbon, 7. Nitrogen, 8. Oxygen, 9. Fluorine, 10. Neon, 11. Sodium, 12. Magnesium, 13. Aluminum, 14. Silicon, 15. Phosphorus, 16. Sulphur, 17. Chlorine, 18. Argon, 19. Potassium and 20. Calcium.
- Now coming to the concept of learning the valencies of the elements.
- We have to find the valence electrons by using the group they are located in.
- Coming to the second period of the periodic table the elements which are present in second row of the periodic table are
Group 1 - Li - has 1 valence electron
Group 2 - Be - has 2 valence electrons
Group 13 - B - has 3 valence electrons
Group 14 - C - has 4 valence electrons
Group 15 - N - has 5 valence electrons
Group 16 - O - has 6 valence electrons
Group 17 - F - has 7 valence electrons
- Coming to third row of the periodic table the elements are
Group 1 - Na - has 1 valence electron
Group 2 - Mg - has 2 valence electrons
Group 13 - Al - has 3 valence electrons
Group 14 - Si - has 4 valence electrons
- Coming to fourth row of the periodic table
Group 1 - K - has 1 valence electron
Group 2 - Ca - has 2 valence electrons.

Note:In the above sequence groups from 3-12 are missed due to the absence of the first 20 elements in the respective groups. It is very easy to learn and remember the valence electrons by following the above said lines.