Chemistry - Mass Number of first 20 elements

Hydrogen (H)

Atomic Number:1

Mass Number : 1

Helium(He)

Atomic Number : 2

Mass Number: 2

Lithium (Li)

Atomic Number: 3

Mass Number: 7

Beryllium (Be)

Atomic Number: 4

Mass Number: 9

Boron (B)

Atomic Number: 5

Mass Number: 11

Carbon (C)

Atomic Number: 6

Mass Number: 12

Nitrogen (N)

Atomic Number: 7

Mass Number: 14

Oxygen (O)

Atomic Number: 8

Mass Number: 16

Fluorine (F)

Atomic Number: 9

Mass Number: 19

Neon (Ne)

Atomic Number: 10

Mass Number: 20

Sodium (Na)

Atomic Number: 11

Mass Number: 23

Magnesium(Mg)

Atomic Number: 12

Mass Number: 24

Aluminium (Al)

Atomic Number: 13

Mass Number: 27

Silicon (Si)

Atomic Number: 14

Mass Number: 28

Phosphorus (P)

Atomic Number: 15

Mass Number: 31

Sulphur (S)

Atomic Number: 16

Mass Number: 32

Chlorine (Cl)

Atomic Number: 17

Mass Number: 35.5

Argon (Ar)

Atomic Number: 18

Mass Number: 40

Potassium (K)

Atomic Number: 19

Mass Number: 39

Calcium (Ca)

Atomic Number: 20

Mass Number: 40