Beryllium (Be)
Beryllium (Be) is an alkaline earth metal with atomic number 4 and a standard atomic weight of 9.0122. At room temperature it is a solid that melts at 1,287 °C and boils at 2,468 °C.
Beryllium key facts
Beryllium at a glance
Identity
| Symbol | Be |
|---|---|
| Atomic number (Z) | 4 |
| Atomic weight | 9.0122 ± 0.0001 (CIAAW 2024) |
| Category | Alkaline earth metal |
| Group | 2 — alkaline earth metals |
| Period | 2 |
| Block | s-block |
| CAS number | 7440-41-7 |
Atomic properties
| Electron configuration | [He] 2s2 Full: 1s2 2s2 |
|---|---|
| Electrons per shell | 2, 2 |
| Oxidation states | +2 Less common: 0, +1 |
| Electronegativity (Pauling) | 1.57 |
| First ionisation energy | 9.323 eV (899.5 kJ/mol) 2nd: 18.211 eV · 3rd: 153.896 eV |
| Atomic radius (empirical) | 105 pm |
| Covalent radius | 102 pm |
| Van der Waals radius | 153 pm |
Physical properties
| State at 25 °C | Solid |
|---|---|
| Melting point | 1,287 °C · 2,348.6 °F · 1,560.15 K |
| Boiling point | 2,468 °C · 4,474.4 °F · 2,741.15 K |
| Density | 1.85 g/cm³ |
| Specific heat capacity | 1.825 J/(g·K) |
| Thermal conductivity | 201 W/(m·K) |
| Crystal structure | Hexagonal |
Isotopes & abundance
| Natural occurrence | Primordial |
|---|---|
| Radioactive | No |
| Natural isotopes (abundance) | 9Be 100% |
| Stable isotopes | 1 |
| Known isotopes | 12 |
| Abundance in Earth's crust | 2.8 mg/kg |
| Abundance in seawater | 0.0000056 mg/L |
Atomic weights: CIAAW Abridged Standard Atomic Weights 2024. Other properties: standard reference compilations, checked October 2026; predicted values are marked.
Beryllium electron configuration
Beryllium has 4 electrons. Written in short form, its ground-state configuration is [He] 2s2 — the electrons of the noble gas helium, plus 2s2.Written out in full: 1s2 2s2.
As a member of group 2 it has 2 valence electrons in its outer shell (shell 2), which largely decide its chemistry.
Discovery and name
1798 — Louis-Nicolas Vauquelin (isolated by Friedrich Wöhler and Antoine Bussy, 1828) · France.
From the mineral beryl.
Known for
A light, stiff metal used in aerospace parts, X-ray windows (it barely absorbs X-rays) and the mirrors of the James Webb Space Telescope. Its dust is highly toxic.
Isotopes of beryllium
Naturally occurring beryllium is a mix of 1 isotope. Each has 4 protons; they differ in the number of neutrons:
| Isotope | Protons | Neutrons | Natural abundance | Stability |
|---|---|---|---|---|
| 9Be | 4 | 5 | 100% | stable |
12 isotopes of beryllium are known in our data set (half-lives as published in nuclear data tables).
Beryllium compared with group 2
The other elements in group 2 (alkaline earth metals), from top to bottom of the table:
| Element | Z | Atomic weight | Melting point | Boiling point | Density | Electronegativity |
|---|---|---|---|---|---|---|
| Beryllium | 4 | 9.0122 | 1,287 °C | 2,468 °C | 1.85 g/cm³ | 1.57 |
| Magnesium | 12 | 24.305 | 650 °C | 1,090 °C | 1.74 g/cm³ | 1.31 |
| Calcium | 20 | 40.078 | 842 °C | 1,484 °C | 1.54 g/cm³ | 1 |
| Strontium | 38 | 87.62 | 777 °C | 1,377 °C | 2.64 g/cm³ | 0.95 |
| Barium | 56 | 137.33 | 727 °C | 1,845 °C | 3.51 g/cm³ | 0.89 |
| Radium | 88 | [226] | 696 °C | 1,737 °C | 5 g/cm³ | 0.9 |