Beryllium – facts and properties
- Symbol
- Be
- Atomic number
- 4
- Atomic mass
- 9.012 u
- Period
- 2
- Group
- 2
- Category
- alkaline earth metal
- Electron configuration
- [He] 2s²
- Electronegativity
- 1.57
- Atomic radius
- 112 pm
- Valence electrons
- 2
- State at standard conditions
- solid
- Melting point
- 1287 °C
- Boiling point
- 2471 °C
- Density
- 1.85 g/cm³
- Discovered
- 1798
Beryllium is a steel-grey metal that is lighter than aluminium yet stiffer than steel. It carries atomic number 4 and is the first of the alkaline earth metals, although its chemistry has more in common with aluminium than with calcium. Few people ever handle the metal itself, but many have seen it in the gemstones emerald and aquamarine. Engineers prize it for telescope mirrors and spacecraft; toxicologists treat its dust with great respect.
Position in the periodic table
Occurrence and extraction
Beryllium is a rare element in the Earth's crust and never occurs as a free metal. It is found in about a hundred minerals, the best known being beryl, a beryllium aluminium silicate. Pure beryl is colourless; traces of chromium turn it green and make emerald, while iron gives the blue of aquamarine or the yellow of heliodor. The main industrial ore today is bertrandite, mined in the state of Utah in the United States, which supplies most of the world's beryllium. Smaller deposits are worked in China, Brazil and Kazakhstan.
Extracting the metal is demanding. The ore is crushed and treated with sulfuric acid, and the solution is purified in several stages to give beryllium hydroxide. This is converted to beryllium fluoride, which is reduced with magnesium at high temperature to give beryllium metal; an alternative route is the electrolysis of molten beryllium chloride. Because beryllium dust and fumes are hazardous, every step runs under strict containment. The element was discovered in 1798 by the French chemist Louis-Nicolas Vauquelin, who showed that beryl and emerald contained a previously unknown earth. The metal was first isolated three decades later. Its early name glucinium referred to the sweet taste of its salts, a property no one would test today.
Properties and reactions
Beryllium has the electron configuration [He] 2s² with two valence electrons, and it sits in period 2 and group 2. It is a light metal with a density of 1.85 g/cm³, yet it is hard, brittle and has an unusually high melting point of 1287 °C for such a light element; it boils at 2471 °C. Its electronegativity of 1.57 is high for an alkaline earth metal, and the Be²⁺ ion is tiny and highly charged. As a result beryllium compounds are not typical ionic salts but have a strong covalent character. Solid beryllium chloride, for example, consists of chains in which chlorine atoms bridge neighbouring beryllium atoms, and even the melt is a poor conductor of electricity.
In air the metal immediately forms a thin, tough layer of beryllium oxide that protects it from further attack. This layer explains why beryllium, unlike magnesium or calcium, does not react even with boiling water. It dissolves in dilute acids with evolution of hydrogen, and it is the only alkaline earth metal that also dissolves in alkalis, because beryllium hydroxide is amphoteric, reacting with both acids and alkalis. Here it behaves like aluminium, its diagonal neighbour in the periodic table. Beryllium is exceptionally transparent to X-rays because its atoms have so few electrons to scatter them. It conducts heat well, expands very little when warmed and is one of the stiffest metals for its weight.
Uses in technology
Most beryllium is used in alloys. Copper containing a few per cent of beryllium is strong, springy, wear-resistant and still a good electrical conductor; it is made into spring contacts for connectors, switches and relays, and into non-sparking tools for refineries and mines where a spark could ignite gas. Pure beryllium is a structural material for aerospace: its stiffness and low mass suit gyroscopes, satellite frames and optical benches, and the eighteen gold-coated mirror segments of the James Webb Space Telescope are beryllium because it holds its shape at extremely low temperatures.
Thin beryllium foils serve as windows in X-ray tubes and detectors, letting the radiation pass almost unhindered. In nuclear reactors beryllium reflects and moderates neutrons, and early neutron sources combined it with radium. Beryllium oxide is a ceramic that conducts heat nearly as well as a metal while insulating electrically, which makes it valuable in high-power electronics and some laser tubes. In everyday life beryllium appears only in gemstones. Because its dust causes lung disease, machining and recycling of the metal are tightly regulated, and manufacturers replace it wherever another material will do.
Quick question
Ionization energy always rises strictly across a period - why does that still not hold for beryllium (Be) and boron (B)?
FAQ
Is beryllium toxic?
Yes. Inhaled beryllium dust or fumes can cause berylliosis, a chronic inflammatory lung disease, and beryllium compounds are classified as carcinogenic. A solid piece of the metal is not hazardous to handle as long as it is not ground, drilled, welded or melted. School laboratories do not use beryllium.
Why is emerald green if beryl is colourless?
The colour comes from impurities, not from beryllium. When a small fraction of the aluminium ions in beryl is replaced by chromium or vanadium ions, these absorb red and blue light and the crystal looks green. Iron impurities instead produce the blue of aquamarine or the yellow of heliodor.
What is beryllium used for in space?
Beryllium is light, extremely stiff and barely changes shape as temperature varies. For mirrors, satellite structures and precision instruments these properties are ideal: every gram of launch mass is expensive, and instruments in space experience extreme cold and large temperature swings.