Bromide

Quick Facts

Formula: Br⁻

Pronunciation: BROH-mide

Etymology: Bromine + -ide

Meaning: The negative ion formed when bromine gains one electron.

What It Really Means

Bromide sits between chloride and iodide in the halogen family, and that middle position gives it interesting properties. It is a good nucleophile, and it is a decent leaving group in organic reactions. In fact, bromide is one of the most common leaving groups in substitution reactions. That is because the C-Br bond is weaker than the C-Cl bond but not as weak as the C-I bond. It strikes a balance. Now here is a common confusion. Bromide, bromine, and bromate are three different things. Bromide is Br minus, the ion. Bromine is Br2, the reddish-brown liquid element. Bromate is BrO3 minus, an oxyanion used in some food products. Same root, different oxidation states, different chemistry. Also, in everyday language, bromide has another meaning. In old medicine, bromides were used as sedatives. And in chemistry, a bromide can also refer to a boring person, though that is not a scientific term. In the lab, silver bromide is a light-sensitive compound used in traditional photography. When light hits it, silver ions reduce to metallic silver, forming the dark image. That is the basis of black-and-white film. So bromide is not just a lab ion. It has shaped how we captured memories for over a century.

Common Examples

• Sodium bromide (NaBr)
• Potassium bromide (KBr)
• Silver bromide (AgBr)
• Hydrobromic acid (HBr)

Related Terms