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Sodium (Na), element 11
Sodium (Na) is the chemical element with atomic number 11: an alkali metal in group 1, period 3. At 25 °C it is a solid, with an atomic mass of 22.99 u.
Physical and chemical data
| Atomic number | 11 |
|---|---|
| Symbol | Na |
| Atomic mass | 22.99 u |
| Density | 0.97 g/cm³ |
| Melting point | 97.8 °C (370.95 K) |
| Boiling point | 882.85 °C (1,156 K) |
| Electronegativity (Pauling) | 0.93 |
| Electron configuration | [Ne]3s1 |
| Atomic radius (van der Waals) | 227 pm |
| Oxidation states | +1 |
| Physical state at 25 °C | solid |
| Family | alkali metal |
| Group and period | 1 / 3 |
| Discoverer and year | Humphry Davy (1807) |
The discovery record belongs to Humphry Davy, in 1807.
Neighbours on the table
Horizontally, one proton less lands on Neon (Z=10); one more lands on Magnesium (Z=12). Vertically, group 1 gathers relatives with similar behaviour: Hydrogen, Lithium, Potassium, Rubidium.
The story behind the name
The English and Portuguese names come from soda, the sodium carbonate of plant ashes; but the symbol Na comes from the Latin natrium, heir to natron, the salt of Lake Natrun that Egyptians used to dry out mummies. Humphry Davy isolated it in 1807 by running electric current through molten caustic soda, days after doing the same for potassium, and watched metallic globules catch fire on contact with water. That is why sodium explodes in water and still seasons your food: in table salt it is chained to chlorine, tamed.
Physical and chemical data: PubChem Periodic Table (NCBI, compiling NIST and IUPAC), public domain, snapshot of 2026-07-10. Temperatures converted from kelvin; historical notes cross checked against classic chemistry references.
Last updated: · Methodology and sources