What is the atomic number of beryllium?

Beryllium has atomic number 4, meaning its nucleus contains exactly four protons. It is the fourth element on the periodic table and the first alkaline earth metal in Period 2.

What is the only stable isotope of beryllium?

Beryllium-9 (⁹Be) is the only stable isotope of beryllium, with five neutrons and 100% natural abundance. Beryllium-10 is a cosmogenic radioisotope produced by cosmic ray spallation in the atmosphere, with a half-life of about 1.39 million years.

What is the electron configuration of beryllium?

Beryllium has the electron configuration 1s² 2s² (or [He] 2s² in noble gas notation). Both valence electrons occupy the 2s orbital, and beryllium typically loses both to form Be²⁺ in compounds. Unlike heavier alkaline earth metals, beryllium often forms covalent bonds due to its small size.

Why is beryllium used in aerospace and nuclear applications?

Beryllium has the highest stiffness-to-weight ratio of any metal (Young's modulus 287 GPa, density 1.85 g/cm³), making it invaluable for aerospace components and gyroscopes. Its low neutron absorption cross-section and high neutron scattering make it a neutron reflector in nuclear reactors.

Yes. Beryllium dust and fumes are highly toxic. Inhalation can cause chronic beryllium disease (berylliosis), a serious and sometimes fatal lung condition. Beryllium and its compounds are classified as carcinogenic. Safe handling requires strict occupational controls and protective equipment.

How was beryllium discovered?

Louis-Nicolas Vauquelin discovered beryllium in 1798 while analyzing the mineral beryl and emerald. He identified a new earth (oxide) distinct from alumina and magnesia. Pure beryllium metal was first isolated independently by Friedrich Wöhler and Antoine Bussy in 1828 by reducing beryllium chloride with potassium.

Beryllium Element Properties

Name: Beryllium Element Properties
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Author: Nham Vu

Complete reference for Beryllium (Be, element 4): atomic data, electron configuration, isotopes, physical constants, and chemical behavior.

4 Be 9.012

Beryllium

Alkaline Earth Metal — Period 2, Group 2

Atomic Identity

Atomic Number

Symbol

Standard Atomic Wt.

9.0121831 u

IUPAC 2021

Period

Group

IIA

Block

s-block

CAS Number

7440-41-7

Discovery

L.-N. Vauquelin

1798

First Isolated

Wöhler & Bussy

1828

Electron Configuration

Full notation 1s² 2s²

Noble gas shorthand [He] 2s²

Electrons per shell 2, 2

Valence electrons 2

Unpaired electrons 0

Spin multiplicity 1 (singlet)

Orbital Diagram

4 electrons (all paired)

Diamagnetic

No unpaired electrons — all orbitals filled

Isotopes of Beryllium

Isotope	Symbol	Protons	Neutrons	Mass (u)	Natural Abundance	Stability
Beryllium-7	⁷Be	4	3	7.01692983	Radioactive	Unstable EC decay, t½ = 53.22 d
Beryllium-9	⁹Be	4	5	9.01218306	100%	Stable
Beryllium-10	¹⁰Be	4	6	10.01353477	Radioactive	Unstable β⁻ decay, t½ = 1.387 × 10⁶ y
Beryllium-11	¹¹Be	4	7	11.02166108	Radioactive	Unstable β⁻ decay, t½ = 13.76 s

Physical Properties

State at STP Solid (metal)

Color Steel-gray

Luster Metallic

Density (25 °C) 1.848 g/cm³

Melting Point 1287 °C (1560 K)

Boiling Point 2469 °C (2742 K)

Heat of Fusion 12.2 kJ/mol

Heat of Vaporization 292 kJ/mol

Specific Heat (25 °C) 16.443 J/(mol·K)

Thermal Conductivity 200 W/(m·K)

Electrical Resistivity 36 nΩ·m (20 °C)

Hardness (Mohs) 5.5

Young's Modulus 287 GPa

Chemical Properties

Electronegativity (Pauling) 1.57

Electron Affinity ≈ 0 kJ/mol (negative)

1st Ionization Energy 899.5 kJ/mol

2nd Ionization Energy 1757.1 kJ/mol

3rd Ionization Energy 14848.7 kJ/mol

Covalent Radius 96 pm

Ionic Radius (Be²⁺) 45 pm

Van der Waals Radius 153 pm

Oxidation States +2 (dominant), 0

Reactivity Amphoteric oxide, dissolves in acid and base

Magnetic Ordering Diamagnetic

Crystal Structure Hexagonal close-packed (hcp)

Ground State Quantum Numbers

Principal (n) 2 (valence electrons)

Azimuthal (l) 0 (s orbital)

Magnetic (mₗ) 0

Spin (mₛ) +½, −½ (paired)

Term symbol ¹S₀

Degeneracy 1 (singlet ground state)

Notable Emission Lines

234.86 nm

UV (deep)

313.04 nm

UV (near)

332.10 nm

UV (near)

457.33 nm

Violet-blue

467.34 nm

Blue

Beryllium produces a white flame in a flame test. Its strongest lines lie in the ultraviolet range, making visual identification challenging without a spectroscope.

Key Facts About Beryllium

Stiffest Structural Metal

Beryllium has the highest Young's modulus (287 GPa) per unit density of any metal. This extraordinary stiffness-to-weight ratio makes it indispensable for precision aerospace components, gyroscopes, and satellite structures.

Nuclear Neutron Moderator

Beryllium-9 has one of the lowest neutron absorption cross-sections of any element and efficiently reflects neutrons. It is used as a neutron reflector and moderator in nuclear reactors and as a neutron source when combined with alpha emitters.

Amphoteric Oxide

Beryllium oxide (BeO) is amphoteric — it dissolves in both strong acids and strong bases. This behavior is more typical of metalloids than metals, reflecting beryllium's diagonal relationship with aluminum in the periodic table.

X-Ray Transparency

Beryllium is almost transparent to X-rays due to its low atomic number. Thin beryllium foils serve as windows in X-ray tubes and detectors, allowing X-rays to pass while maintaining a vacuum seal.

High Melting Point

With a melting point of 1287 °C, beryllium has an unusually high melting point for such a light metal (density 1.85 g/cm³). This thermal stability, combined with its high specific heat, makes it useful in heat-shield and brake applications.

Occupational Hazard

Beryllium dust and soluble compounds are among the most toxic industrial materials. Chronic beryllium disease (berylliosis) causes irreversible lung scarring. OSHA sets the permissible exposure limit at just 0.2 µg/m³ averaged over an 8-hour work shift.

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Summary