Beryllium (Be)
Beryllium is the 4th element, a alkaline earth metal in the s-block. Its standard atomic weight is 9.012.
Beryllium
9.012
What the table records
- Atomic number
- 4
- Standard atomic weight
- 9.012
- Group
- 2
- Period
- 2
- Block
- s-block
- Category
- Alkaline earth metal
- [He] 2s2
- Valence electrons
- 2
- Typical valence
- 2
- Van der Waals radius
- 1.9 Å
- Covalent radius
- 0.96 Å
Molecules containing beryllium
How to read these numbers
The standard atomic weight is an average over the isotopes as they occur naturally, which is why it is rarely a whole number. It is the figure a molar mass calculation uses. Work in mass spectrometry wants the monoisotopic mass of a single isotope instead, which is a different number.
The two radii are not the same measurement. The covalent radius is half the distance between two bonded atoms of the element; the van der Waals radius is how close a non-bonded atom gets before repulsion takes over, and is always the larger. Space-filling models are drawn with the second, ball-and-stick models with the first — which is why the same molecule looks so different in the two.