Br Bromine

Quick answerBromine (Br) is a halogen with atomic number 35 and an atomic mass of 79.904 (2023), in group 17, period 4. It was discovered by Antoine Jérôme Balard in 1826. It is used for flame retardants and pharmaceuticals. Its electron configuration is [Ar] 3d10 4s2 4p5.

Bromine is one of only two elements that is liquid at room temperature, used in flame retardants, medicines, and drilling fluids.

Key facts

Symbol	Br
Atomic number	35
Atomic mass	79.904 (IUPAC standard atomic weight, 2023)
Category	halogen
Group	17
Period	4
Block	p-block
Electron configuration	[Ar] 3d10 4s2 4p5
Discovered	Antoine Jérôme Balard, 1826
Uses	flame retardants, pharmaceuticals, drilling fluids, photography, water treatment

Quick quiz

Three questions from the facts on this page. No sign-up, no score is saved.

1. What is the chemical symbol of Bromine?

F Br Cl I

2. What is the atomic number of Bromine?

37 36 34 35

3. Which category does Bromine belong to?

noble gas transition metal halogen alkali metal

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Keep exploring

• Periodic table — all 118 elements
• Fluorine (F) — another halogen, atomic number 9
• Chlorine (Cl) — another halogen, atomic number 17
• Iodine (I) — another halogen, atomic number 53
• Astatine (At) — another halogen, atomic number 85
• Tennessine (Ts) — another halogen, atomic number 117

Sources & last updated

• CIAAW — Standard Atomic Weights
• PubChem Periodic Table
• Wikipedia — Timeline of chemical element discoveries

Last updated: 2026-11-12. Figures are shown with their year; where sources disagree, the value is left out rather than estimated.