Sodium (Na)
Sodium (Na) is an alkali metal with atomic number 11 and a standard atomic weight of 22.990. At room temperature it is a solid that melts at 98 °C and boils at 883 °C.
Sodium key facts
Sodium at a glance
Identity
| Symbol | Na |
|---|---|
| Atomic number (Z) | 11 |
| Atomic weight | 22.990 ± 0.001 (CIAAW 2024) |
| Category | Alkali metal |
| Group | 1 — alkali metals (with hydrogen) |
| Period | 3 |
| Block | s-block |
| CAS number | 7440-23-5 |
Atomic properties
| Electron configuration | [Ne] 3s1 Full: 1s2 2s2 2p6 3s1 |
|---|---|
| Electrons per shell | 2, 8, 1 |
| Oxidation states | +1 Less common: -1, 0 |
| Electronegativity (Pauling) | 0.93 |
| First ionisation energy | 5.139 eV (495.8 kJ/mol) 2nd: 47.286 eV · 3rd: 71.62 eV |
| Electron affinity | 0.548 eV |
| Atomic radius (empirical) | 180 pm |
| Covalent radius | 155 pm |
| Van der Waals radius | 227 pm |
Physical properties
| State at 25 °C | Solid |
|---|---|
| Melting point | 97.79 °C · 208 °F · 370.94 K |
| Boiling point | 882.9 °C · 1,621.3 °F · 1,156.09 K |
| Density | 0.97 g/cm³ |
| Specific heat capacity | 1.228 J/(g·K) |
| Thermal conductivity | 142 W/(m·K) |
| Crystal structure | Body-centred cubic |
Isotopes & abundance
| Natural occurrence | Primordial |
|---|---|
| Radioactive | No |
| Natural isotopes (abundance) | 23Na 100% |
| Stable isotopes | 4 |
| Known isotopes | 23 |
| Abundance in Earth's crust | 23,600 mg/kg |
| Abundance in seawater | 10,800 mg/L |
Atomic weights: CIAAW Abridged Standard Atomic Weights 2024. Other properties: standard reference compilations, checked October 2026; predicted values are marked.
Sodium electron configuration
Sodium has 11 electrons. Written in short form, its ground-state configuration is [Ne] 3s1 — the electrons of the noble gas neon, plus 3s1.Written out in full: 1s2 2s2 2p6 3s1.
As a member of group 1 it has 1 valence electron in its outer shell (shell 3), which largely decides its chemistry.
Discovery and name
1807 — Humphry Davy · England.
English 'soda'; the symbol Na is from Latin natrium.
Known for
A soft, highly reactive metal stored under oil. As sodium chloride it is table salt; sodium vapour lamps give the yellow light of older street lamps.
Isotopes of sodium
Naturally occurring sodium is a mix of 1 isotope. Each has 11 protons; they differ in the number of neutrons:
| Isotope | Protons | Neutrons | Natural abundance | Stability |
|---|---|---|---|---|
| 23Na | 11 | 12 | 100% | stable |
23 isotopes of sodium are known in our data set (half-lives as published in nuclear data tables).
Sodium compared with group 1
The other elements in group 1 (alkali metals (with hydrogen)), from top to bottom of the table:
| Element | Z | Atomic weight | Melting point | Boiling point | Density | Electronegativity |
|---|---|---|---|---|---|---|
| Hydrogen | 1 | 1.0080 | -259 °C | -253 °C | 0.0899 g/L | 2.2 |
| Lithium | 3 | 6.94 | 180 °C | 1,342 °C | 0.534 g/cm³ | 0.98 |
| Sodium | 11 | 22.990 | 98 °C | 883 °C | 0.97 g/cm³ | 0.93 |
| Potassium | 19 | 39.098 | 64 °C | 759 °C | 0.89 g/cm³ | 0.82 |
| Rubidium | 37 | 85.468 | 39 °C | 688 °C | 1.53 g/cm³ | 0.82 |
| Cesium | 55 | 132.91 | 28 °C | 671 °C | 1.873 g/cm³ | 0.79 |
| Francium | 87 | [223] | 21 °C (est.) | — | 1.87 g/cm³ (pred.) | 0.7 |