| Quantity | Value | Units | Value | Units |
| Atomic number | 18 | |||
| Atomic mass | 39.948(1) | g mole-1 | ||
| Density | 1.40 | g cm-3 | ||
| Mean excitation energy | 188.0 | eV | ||
| Minimum ionization | 1.508 | MeV g-1cm2 | 2.105 | MeV cm-1 |
| Nuclear collision length | 75.7 | g cm-2 | 54.25 | cm |
| Nuclear interaction length | 119.7 | g cm-2 | 85.77 | cm |
| Pion collision length | 101.3 | g cm-2 | 72.58 | cm |
| Pion interaction length | 149.0 | g cm-2 | 106.7 | cm |
| Radiation length | 19.55 | g cm-2 | 14.00 | cm |
| Critical energy | 32.84 | MeV (for e-) | 31.91 | MeV (for e+) |
| Molière radius | 12.62 | g cm-2 | 9.043 | cm |
| Plasma energy |
22.85 | eV | ||
| Muon critical energy | 485. | GeV | ||
| Melting point | 83.79 | K | -189.4 | C |
| Boiling point @ 1 atm | 87.30 | K | -185.9 | C |
| Index of refraction (@ STP, Na D) | 1.23 |