Period 3 of the Periodic Table
Period 3 of the periodic table has 8 elements, from Sodium (Na) to Argon (Ar). The period number usually equals the number of electron shells of the atom, and in this period the 3s and 3p subshells are filled. Moving left to right across a period, the atomic number increases and the atomic radius usually decreases.
Element list
| Atomic no. | Symbol | Name | Atomic mass | Phase | Short configuration |
|---|---|---|---|---|---|
| 11 | Na | Sodium | 22.99 | Solid | [Ne] 3s¹ |
| 12 | Mg | Magnesium | 24.305 | Solid | [Ne] 3s² |
| 13 | Al | Aluminum | 26.982 | Solid | [Ne] 3s² 3p¹ |
| 14 | Si | Silicon | 28.085 | Solid | [Ne] 3s² 3p² |
| 15 | P | Phosphorus | 30.974 | Solid | [Ne] 3s² 3p³ |
| 16 | S | Sulfur | 32.06 | Solid | [Ne] 3s² 3p⁴ |
| 17 | Cl | Chlorine | 35.45 | Gas | [Ne] 3s² 3p⁵ |
| 18 | Ar | Argon | 39.95 | Gas | [Ne] 3s² 3p⁶ |
Frequently asked questions
How many elements are in period 3 of the periodic table?
Period 3 of the periodic table has 8 elements.
Which elements are in period 3?
The elements of period 3 run from Sodium to Argon: Sodium (Na), Magnesium (Mg), Aluminum (Al), Silicon (Si), Phosphorus (P), Sulfur (S), Chlorine (Cl) and Argon (Ar).