Boron
Boron is a chemical element with the symbol B and atomic number 5. It has a standard atomic weight of 10.81, sits in period 2 and group 13, and is classified as a metalloid.
Properties
| Symbol | B |
|---|---|
| Atomic number | 5 |
| Standard atomic weight | 10.81 |
| Category | Metalloid |
| Group | 13 |
| Period | 2 |
| Electron configuration | [He] 2s2 2p1 |
| Outer-shell electrons | 3 |
The figure of 10.81 is a conventional value, because IUPAC publishes an interval for this element rather than a single weight. For elements like this one the fourth digit carries real uncertainty, because the isotopic composition varies measurably between natural sources — so quoting eight digits would overstate what is known.
Compounds containing boron
4 of the compounds in this reference contain B, listed by the fraction of their mass it makes up.
| Compound | Formula | Atoms | % by mass |
|---|---|---|---|
| boron nitride | BN | 1 | 43.6% |
| sodium borohydride | BH4Na | 1 | 28.6% |
| boric acid | BH3O3 | 1 | 17.5% |
| borax | B4H20Na2O17 | 4 | 11.3% |
Calculate with boron
- Molar mass of any formula containing it
- Electron configuration, including ions
- Effective nuclear charge by Slater's rules
- Average atomic mass from isotope abundances
Group 13
Atomic weights are the IUPAC 2021 standard values, abridged to the conventional five significant figures. Group, period, category and electron configuration are derived from the atomic number rather than stored, so they cannot drift out of step with it.