Lithium (Li)
Lithium (Li) is an alkali metal with atomic number 3 and a standard atomic weight of 6.94. At room temperature it is a solid that melts at 180 °C and boils at 1,342 °C.
Lithium key facts
Lithium at a glance
Identity
| Symbol | Li |
|---|---|
| Atomic number (Z) | 3 |
| Atomic weight | 6.94 ± 0.06 (CIAAW 2024) |
| Category | Alkali metal |
| Group | 1 — alkali metals (with hydrogen) |
| Period | 2 |
| Block | s-block |
| CAS number | 7439-93-2 |
Atomic properties
| Electron configuration | [He] 2s1 Full: 1s2 2s1 |
|---|---|
| Electrons per shell | 2, 1 |
| Oxidation states | +1 |
| Electronegativity (Pauling) | 0.98 |
| First ionisation energy | 5.392 eV (520.2 kJ/mol) 2nd: 75.64 eV · 3rd: 122.454 eV |
| Electron affinity | 0.618 eV |
| Atomic radius (empirical) | 145 pm |
| Covalent radius | 133 pm |
| Van der Waals radius | 182 pm |
Physical properties
| State at 25 °C | Solid |
|---|---|
| Melting point | 180.5 °C · 356.9 °F · 453.65 K |
| Boiling point | 1,342 °C · 2,447.6 °F · 1,615.15 K |
| Density | 0.534 g/cm³ |
| Specific heat capacity | 3.582 J/(g·K) |
| Thermal conductivity | 84.8 W/(m·K) |
| Crystal structure | Body-centred cubic |
Isotopes & abundance
| Natural occurrence | Primordial |
|---|---|
| Radioactive | No |
| Natural isotopes (abundance) | 7Li 95.15%, 6Li 4.85% |
| Stable isotopes | 3 |
| Known isotopes | 11 |
| Abundance in Earth's crust | 20 mg/kg |
| Abundance in seawater | 0.18 mg/L |
Atomic weights: CIAAW Abridged Standard Atomic Weights 2024. Other properties: standard reference compilations, checked October 2026; predicted values are marked.
Lithium electron configuration
Lithium has 3 electrons. Written in short form, its ground-state configuration is [He] 2s1 — the electrons of the noble gas helium, plus 2s1.Written out in full: 1s2 2s1.
As a member of group 1 it has 1 valence electron in its outer shell (shell 2), which largely decides its chemistry.
Discovery and name
1817 — Johan August Arfwedson · Sweden.
Greek lithos, stone — it was found in a mineral rather than in plants.
Known for
The lightest metal, soft enough to cut with a knife. Its main use today is in rechargeable lithium-ion batteries; lithium salts are also used to treat bipolar disorder.
Isotopes of lithium
Naturally occurring lithium is a mix of 2 isotopes. Each has 3 protons; they differ in the number of neutrons:
| Isotope | Protons | Neutrons | Natural abundance | Stability |
|---|---|---|---|---|
| 7Li | 3 | 4 | 95.15% | stable |
| 6Li | 3 | 3 | 4.85% | stable |
11 isotopes of lithium are known in our data set (half-lives as published in nuclear data tables).
Lithium 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 |