Phosphorus vs Arsenic
Phosphorus and Arsenic 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 Arsenic wears.
Side by side
| Property | Phosphorus | Arsenic |
|---|---|---|
| Symbol | P | As |
| Atomic number (Z) | 15 | 33 |
| Atomic mass | 30.974 u | 74.922 u |
| Category | Nonmetal | Metalloid |
| Group | 15 | 15 |
| Period | 3 | 4 |
| Phase at room temp | solid | solid |
| Electron configuration | [Ne] 3s^2 3p^3 | [Ar] 3d^10 4s^2 4p^3 |
| Valence electrons | 5 | 5 |
| Atomic radius | 98 pm | 114 pm |
| Electronegativity | 2.19 | 2.18 |
| First ionisation energy | 1012 kJ/mol | 947 kJ/mol |
The verdicts
- Bigger atom: Arsenic — the lower an element sits in its group, the more shells it wears.
- Greedy electron-taker: Phosphorus — higher electronegativity means it pulls shared electrons harder.
- Heavier: Arsenic — 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.