All practice pages/Interatomic theory/Elements
Element 35, a halogen
The only nonmetal that is a liquid at room temperature: dark red, heavy, fuming, and named for its smell.
Period 4, group 17: the third rung down the stem of the 7. The other halogens are tinted, and every cell opens its own article.
Bromine has 35 electrons, one for every proton, so the atom carries no charge. Below are the same 35 electrons written two ways.
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁵
Short form: [Ar] 3d¹⁰ 4s² 4p⁵, where [Ar] stands for the 18 electrons argon already has.
That list runs by shell. In the order the subshells fill it reads [Ar] 4s² 3d¹⁰ 4p⁵, because a subshell fills by its energy, not by its shell number.
The simple form counts electrons shell by shell. The orbital form says which subshell each one sits in: s holds 2, p holds 6, d holds 10 and f holds 14. Shell 3 here is 3s² 3p⁶ 3d¹⁰, and 2 + 6 + 10 is 18.
Bromine sits in period 4 and has 4 shells. The period number counts the shells.
The outer shell holds 7 electrons. Those are the ones bromine can lose, gain or share, so they are the ones that decide what it bonds with. For a main-group element the group number gives that count: group 17 means 7.
Seven valence electrons, one short of a full shell, so it gains one to form the Br⁻ ion or shares one in a covalent bond.
Seven valence electrons, one short of eight. Two bromine atoms share one pair, a single bond.
Rare in rock, about 0.0004% of the crust, but seawater holds about 65 mg of bromide per liter and some brines hold far more. The Dead Sea and the deep brines under Arkansas and Michigan are the main sources.
Antoine Jérôme Balard, a 23-year-old pharmacy student in Montpellier, isolated it from salt-marsh brine in 1826. Carl Löwig had found it a year earlier in Germany but published later. The name is from the Greek bromos, stench.
Bromine compounds make flame retardants for plastics and electronics, dense drilling fluids for oil wells, pool and spa sanitizers, and some medicines and dyes. Silver bromide was the light-sensitive layer of photographic film.