What are the atomic numbers of first 20 elements?

Answer 1

Atomic Mass of the mainly occurring isotopes) of the first 20 elements (rounded figures)

Ordering on atomic number 1 - 20

1 H

4 He

7 Li

9 Be

11 B

12 C

14 N

16 O

19 F

20 Ne

23 Na

24 Mg

27 Al

28 Si

31 P

32 S

35.5 Cl

36 Ar

39 K

40 Ca

*) But actually there are about 85 'different mass' isotopes from these 20 elements.

• K on its own already has 4 different isotopes with mass numbers, ranging from 39 to 42

• Ca on its own already has 9 different isotopes with mass numbers, ranging from 40 to 48

Answer 2

The Atomic number is the number of protons (positive charges) in the nucleus. So the very simple answer is Hydrogen has 1 proton, so Atomic number is 1 all the way up to Calcium, 20 protons with Atomic number 20. The significant fact here is that the atomic number defines the element.

Answer 3

These are the atomic mass values of the first 20 atoms, numbered 1 to 20:

1. Hydrogen = 1.0079
2. Helium = 4.0026
3. Lithium = 6.941
4. Berillium = 9.0122
5. Boron = 10.811
6. Carbon = 12.011
7. Nitrogen = 14.0067
8. Oxygen = 15.999
9. Fluorine = 18.998
10. Neon = 20.1797
11. Sodium = 22.9897
12. Magnesium = 24.305
13. Aluminium = 26.9815
14. Silicon = 28.0855
15. Phosphorus = 30.97376
16. Sulphur = 32.066
17. Chlorine = 35.4527
18. Argon = 39.948
19. Potassium = 39.0983
20. Calcium = 40.078

Answer 4

This question can be answered by any Periodic Table. The atomic number is the number of protons in the nucleus of an atom of that particular element. The atomic number must be a counting number (1,2,3,4...) and the atomic number increases by increments of one from left to right across each row. The sequence is continued of the next row, for instance neon's atomic number is 10, the next row starts with sodium; atomic number 11.

Answer 5

Hydrogen: 0 Helium: 2 Lithium: 4 Beryllium: 5 Boron: 6 Carbon: 6 Nitrogen: 7 Oxygen: 8 Fluorine: 10 Neon: 10 Sodium: 12 Magnesium: 12 Aluminum: 14 Silicon: 14 Phosphorus: 16 Sulfur: 16 Chlorine: 18 Argon: 22 Potassium: 20 Calcium: 20

Answer 6

The number of neutrons in an element is not fixed. This is why "isotopes" of elements exist. Take the simplest atom, that of Hydrogen, this can have 0, 1 or 2 neutrons.

Thus you can see that your question is far to broad to elicit a simple answer.

Answer 7

Starting from

Hydrogen (H) atomic number 1

Helium (He) atomic number 2

Lithium (Li) atomic number 3

Beryllium (Be) atomic number 4

Boron (B) atomic number 5

Carbon (C) atomic number 6

Nitrogen (N) atomic number 7

Oxygen (O) atomic number 8

Fluorine (F) atomic number 9

Neon (Ne) atomic number 10

Sodium (Na) atomic number 11

Magnesium (Mg) atomic number 12

Aluminum (Al) atomic number 13

Silicon (Si) atomic number 14

Phosphorus (P) atomic number 15

Sulfur (S) atomic number 16

Chlorine (Cl) atomic number 17

Argon (Ar) atomic number 18

Potassium (K) atomic number 19

Calcium (Ca) atomic number 20.

Answer 8

Hydrogen: 1 proton

Helium: 2 protons

Lithium: 3

Beryllium: 4

Boron: 5

Carbon: 6

Nitrogen: 7

Oxygen: 8

Fluorine: 9

Neon: 10

Sodium: 11

Magnesium: 12

Aluminum: 13

Silicon: 14

Phosphorus: 15

Sulfur: 16

Chlorine: 17

Argon: 18

Potassium: 19

Calcium: 20

Answer 9

Mass numbers refer to the numbers of protons and neutrons in the nuclei of specific isotopes. It would be easier to ask for the atomic weights of the first 20 elements on the periodic table, because they are written along with element's symbol and atomic number. If you really want to know the mass numbers of the isotopes of the first 20 elements, I recommend looking up the Wikipedia article for each element.