First 20 elements
Now that we understand what symbols, atomic numbers and atomic masses are, we are ready to focus on the first 20 elements of the periodic table.
A list of the first 20 elements is shown below:
| Element | Symbol | Atomic Number | Atomic Mass | Number of Protons | Number of Neutrons |
| Hydrogen | H | 1 | 1 | 1 | 0 |
| Helium | He | 2 | 4 | 2 | 2 |
| Lithium | Li | 3 | 7 | 3 | 4 |
| Beryllium | Be | 4 | 9 | 4 | 9 |
| Boron | B | 5 | 11 | 5 | 6 |
| Carbon | C | 6 | 12 | 6 | 6 |
| Nitrogen | N | 7 | 14 | 7 | 7 |
| Oxygen | O | 8 | 16 | 8 | 8 |
| Fluorine | F | 9 | 18 | 9 | 9 |
| Neon | Ne | 10 | 20 | 10 | 20 |
| Sodium | Na | 11 | 23 | 11 | 12 |
| Magnesium | Mg | 12 | 24 | 12 | 12 |
| Aluminum | Al | 13 | 27 | 13 | 14 |
| Silicon | Si | 14 | 28 | 14 | 14 |
| Phosphorous | P | 15 | 31 | 15 | 16 |
| Sulphur | S | 16 | 32 | 16 | 16 |
| Chlorine | Cl | 17 | 35 | 17 | 16 |
| Argon | Ar | 18 | 40 | 18 | 22 |
| Potassium | K | 19 | 39 | 19 | 20 |
| Calcium | Ca | 20 | 40 | 20 | 20 |