Bromine
Bromine is a chemical element with the symbol Br and atomic number 35. It has a standard atomic weight of 79.904, sits in period 4 and group 17, and is classified as a halogen.
Properties
| Symbol | Br |
|---|---|
| Atomic number | 35 |
| Standard atomic weight | 79.904 |
| Category | Halogen |
| Group | 17 |
| Period | 4 |
| Electron configuration | [Ar] 3d10 4s2 4p5 |
| Outer-shell electrons | 7 |
The figure of 79.904 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 bromine
4 of the compounds in this reference contain Br, listed by the fraction of their mass it makes up.
| Compound | Formula | Atoms | % by mass |
|---|---|---|---|
| sodium bromide | BrNa | 1 | 77.7% |
| potassium bromate | BrKO3 | 1 | 47.8% |
| eosin | C20H6Br4Na2O5 | 4 | 46.2% |
| bromothymol blue | C27H28Br2O5S | 2 | 25.6% |
Calculate with bromine
- 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 17
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.