Lithium
Lithium (Li) is an alkali metal with atomic number 3 and an atomic mass of 6.94. Its electron configuration is [He] 2s1, which gives it 1 valence electron.
Lithium key data
| Symbol | Li |
|---|---|
| Atomic number | 3 |
| Atomic mass (standard atomic weight) | 6.94 |
| Molar mass | 6.94 g/mol |
| Protons | 3 |
| Neutrons (most abundant isotope, lithium-7) | 4 |
| Electrons (neutral atom) | 3 |
| Valence electrons | 1 |
| Category | Alkali metal |
| Period | 2 |
| Group | 1 |
| Block | s-block |
| Noble gas notation | [He] 2s1 |
| Full electron configuration | 1s2 2s1 |
| Electrons per shell | 2, 1 |
Atomic mass: IUPAC CIAAW abridged standard atomic weights, 2024. Most abundant isotope: NIST Atomic Weights and Isotopic Compositions.
The values are facts and free to use; this page’s selection and presentation are © 2026 ScienceQuest.
Measured properties of lithium
From PubChem, the US National Institutes of Health. Public domain.
| Melting point | 453.65 K (180.5 °C), 80th of 103 by melting point |
|---|---|
| Boiling point | 1615 K (1341.9 °C), 64th of 93 by boiling point |
| Density | 0.534 g/cm³, 85th of 96 by density |
| State at room temperature | Solid |
| Electronegativity | 0.98 (Pauling), 87th of 95 by electronegativity |
| Van der Waals radius | 182 pm, 80th of 99 by atomic radius |
| First ionisation energy | 5.392 eV (520.2 kJ/mol), 94th of 102 by first ionisation energy |
| Electron affinity | 0.618 eV (59.6 kJ/mol), 34th of 57 by electron affinity |
| Common oxidation states | +1 |
| Discovered | 1817 |
Each rank counts down from the highest value, among the elements PubChem’s table gives one for, and links to that property ranked across the whole table. All of them are collected under periodic trends.
Lithium electron configuration
The full electron configuration of lithium is 1s2 2s1. With the noble-gas core collapsed it is [He] 2s1, and the outermost subshell is 2s1.
Why group and block follow from this is set out in how the periodic table maps electron configuration, and the electron configuration of every element is listed on one page.
Mass of one lithium atom
A molar mass is grams per mole, so dividing by the Avogadro constant gives the mass of a single atom, or for an element with more than one natural isotope the average mass of its atoms, and the reciprocal gives how many atoms sit in a gram.
Mass of one atom
- one atom = 6.94 / (6.02214076 × 10²³)
- = 1.1524 × 10⁻²³ g
Atoms in one gram
- atoms per gram = 6.02214076 × 10²³ / 6.94
- = 8.6774 × 10²² atoms
Lithium on the periodic table
Lithium is in period 2, group 1, in the s-block.
The other elements of group 1 are hydrogen, sodium, potassium, rubidium, caesium and francium.