Beryllium (Be)
Element 4 · Alkaline earth metal · atomic mass 9.0122 u · group 2, period 2
Electron shells: 2, 2
Beryllium is a stiff, remarkably light metal that is transparent to X-rays and does not go brittle at low temperatures. Its dust is severely toxic, which limits where it can be worked.
The James Webb Space Telescope's mirrors are beryllium — it barely changes shape as it cools to 40 K.
- Atomic number
- 4
- Atomic mass
- 9.0122 u
- Electron configuration
- [He] 2s²
- Group · period · block
- 2 · 2 · s
- Oxidation states
- +2
- Electronegativity
- 1.57 (Pauling)
- Melting point
- 1,287 °C
- Boiling point
- 2,471 °C
- Density
- 1.85 g/cm³
- State at 20 °C
- Solid
- Appearance
- Hard, grey-white metal
- Discovered
- Louis-Nicolas Vauquelin, 1798
4 protons, and 4 electrons when neutral
IUPAC standard atomic weight
Alkaline earth metals
What Beryllium is used for
- X-ray window foils
- Beryllium-copper non-sparking tools
- Aerospace structures and mirrors
- Neutron reflectors in reactors
Atomic structure of Beryllium
A neutral beryllium atom has 4 protons and 4 electrons. Its most common isotope carries about 5 neutrons, which is where the mass number 9 comes from. Change the neutron count and you have a different isotope of beryllium; change the proton count and you have a different element entirely.
Those electrons fill shells from the inside out: 2, 2. In orbital notation that is [He] 2s², leaving 2 valence electrons in the outer shell — the ones that do the chemistry.
3D electron orbitals
See where Beryllium's electrons actually are — a cloud of 26,000 points sampled from the probability density |ψ|², not a cartoon of a lobe.
Where Beryllium sits in the periodic table
Discovery and naming
Beryllium was discovered by Louis-Nicolas Vauquelin in 1798. Its name comes from The mineral beryl, via Greek beryllos.
Keep exploring
Atomic weight from IUPAC/CIAAW; physical properties from PubChem (US National Library of Medicine). Values that have never been measured are shown as “not measured” rather than estimated.
Related Calculators
Frequently Asked Questions
What is the atomic mass of Beryllium?
The standard atomic weight of Beryllium is 9.0122 u, as published by IUPAC's Commission on Isotopic Abundances and Atomic Weights.
How many protons, neutrons and electrons does Beryllium have?
Beryllium has 4 protons, because the atomic number is the proton count and that is what makes an atom Beryllium at all. A neutral Beryllium atom has the same number of electrons, 4. The neutron count varies by isotope; the most common one has about 5, since 9 − 4 = 5.
What is the electron configuration of Beryllium?
The electron configuration of Beryllium is [He] 2s². Its electrons are arranged 2, 2 across 2 shells.
Is Beryllium a metal?
Yes. Beryllium is classified as a alkaline earth metal, on the left side of the table.
What group and period is Beryllium in?
Beryllium is in group 2 (the alkaline earth metals), period 2, in the s-block. The group is its column and the period is its row.
What is the charge of Beryllium?
Beryllium most commonly forms a 2+ ion. It has 2 electrons in its outer shell and loses them readily, which is what the group number tells you.
What is the melting point of Beryllium?
Beryllium melts at 1,287 °C and boils at 2,471 °C. That puts it in the solids at everyday temperatures.
What is Beryllium used for?
X-ray window foils, Beryllium-copper non-sparking tools, Aerospace structures and mirrors, Neutron reflectors in reactors. Beryllium is a stiff, remarkably light metal that is transparent to X-rays and does not go brittle at low temperatures.
Who discovered Beryllium, and where does its name come from?
Beryllium (Be) was discovered by Louis-Nicolas Vauquelin in 1798. The name comes from The mineral beryl, via Greek beryllos.