Sulfur vs Selenium
Sulfur and Selenium sit in the same column of the periodic table — same family, one period apart — so almost every difference between them comes from one thing: the extra electron shell Selenium wears.
Side by side
| Property | Sulfur | Selenium |
|---|---|---|
| Symbol | S | Se |
| Atomic number (Z) | 16 | 34 |
| Atomic mass | 32.06 u | 78.971 u |
| Category | Nonmetal | Nonmetal |
| Group | 16 | 16 |
| Period | 3 | 4 |
| Phase at room temp | solid | solid |
| Electron configuration | [Ne] 3s^2 3p^4 | [Ar] 3d^10 4s^2 4p^4 |
| Valence electrons | 6 | 6 |
| Atomic radius | 88 pm | 103 pm |
| Electronegativity | 2.58 | 2.55 |
| First ionisation energy | 1000 kJ/mol | 941 kJ/mol |
The verdicts
- Bigger atom: Selenium — the lower an element sits in its group, the more shells it wears.
- Greedy electron-taker: Sulfur — higher electronegativity means it pulls shared electrons harder.
- Heavier: Selenium — compare the atomic masses in the table above.
Want the visual version with bars for radius, electronegativity and ionisation energy? Open the interactive compare tool with this pair already loaded.