Question

What is the atomic mass of elements from 1 to 20?

Answer 1

Atomic mass of an element is the sum of it's proton and neutron.
the atomic Mass of element s from one to twenty are given below
1 Hydrogen 1
2 Helium 4
3Lithium 7
4 Beryllium 9
5 Boron 10
6 Carbon 12
7 Nitrogen 14
8 Oxygen 16
9 Flourine 19
10. Neon 20
11 Sodium 23
12 Magnesium 24
13 aluminum 27
14 Silicon 28
15 Phosphorus 31
16 Sulphur 32
17 Chlorine 35.5
18 Argon 40
19 Potassium 39
20 Calcium 40

Answer 2

Atomic mass means the sum of the number of protons and number of neutrons in the nucleus.

At. Mass = No. of protons + No. of Neutrons

For neutral atom,

Atomic mass = No. of electrons + No. of neutrons.

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1. Hydrogen  = 1
2. Helium = 4
3. Lithium = 7
4. Beryllium = 9
5. Boron = 10
6. Carbon = 12
7. Nitrogen = 14
8. Oxygen = 16
9. Florine = 19
10. Neon = 20
11. Sodium = 23
12. Magnesium = 24
13. Aluminium = 27
14. Silicon = 28
15. Phosphorus = 31
16. Sulphur = 32
17. Chlorine = 35.5
18. Argon = 40
19. Potassium = 39
20. Calcium = 40

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Hope it helps.