--- title: "Br- Bromide Ion | Intro to Chemistry" description: "Br- is the bromide ion, a negatively charged bromine atom that forms ionic compounds with cations in Intro to Chemistry." canonical: "https://fiveable.me/intro-chem/key-terms/br" type: "key-term" subject: "Intro to Chemistry" unit: "Unit 7" --- # Br- Bromide Ion | Intro to Chemistry ## Definition Br- is the bromide ion, a bromine atom with a 1- charge. In Intro to Chemistry, it shows up when you identify anions and predict how bromide pairs with cations in ionic compounds. ## What It Is Br- is the bromide ion, which means a bromine atom has gained one electron and now carries a 1- charge. In Intro to Chemistry, you use this symbol when you are naming ions, writing formulas for ionic compounds, and checking whether the charges add up correctly. Bromine is a halogen, and halogens usually form negative ions by gaining one electron. That extra electron gives bromide a full outer shell, which makes it more stable than neutral bromine in many ionic settings. The symbol Br- is not just a label, it tells you both the element and the charge. Because bromide has a single negative charge, it pairs with cations in a ratio that makes the overall compound neutral. For example, a +1 ion like Na+ pairs with Br- to make NaBr. A +2 ion would need two bromide ions, because two 1- charges are needed to balance one 2+ charge. This charge balancing is the main chemistry move tied to Br-. When you see it in formulas, you should think about ionic bonding, not a standalone molecule. Bromide ions are held in place by electrostatic attraction to positive ions, and the exact formula depends on electrical neutrality. One easy mistake is to treat Br- like a neutral atom or to forget the charge when naming compounds. Another is to mix up bromine and bromide. Bromine is the element, while bromide is the anion formed after electron gain. That difference matters any time you are writing ionic formulas, naming salts, or checking whether a compound is correctly balanced. ## Why It Matters Br- matters because ionic bonding in Intro to Chemistry is really about charge matching. If you can identify bromide as a 1- anion, you can build correct formulas, predict the ratio of ions in a compound, and spot when a written formula does not satisfy electrical neutrality. It also gives you practice with the bigger pattern for halogens. Bromide behaves like Cl- and other halide ions, so once you understand one of them, you can transfer the same charge-balancing logic to similar problems. That is a common skill in formula writing, compound naming, and checking work on problem sets. Br- also shows up as a quick check for how ionic compounds are structured. A formula such as MgBr2 tells you magnesium is Mg2+ and bromide is Br-. If you can read the ion charge from the symbol, you can reverse-engineer the compound instead of memorizing every formula one by one. ## Connections ### Bromine Bromine is the neutral element, while Br- is the bromide ion formed after bromine gains an electron. That difference matters in formula writing because neutral bromine and bromide do not behave the same way. If a problem gives you Br- or a bromide salt, you are dealing with the anion, not elemental bromine. ### Ionic Bond Br- forms ionic bonds by attracting positive ions through electrostatic force. The bond is not about sharing electrons equally, it is about opposite charges pulling together. When you write an ionic formula, bromide tells you one side of the charge balance you need to solve. ### [Electrical Neutrality](/intro-chem/key-terms/electrical-neutrality) Every ionic compound built from Br- has to end up electrically neutral. Since bromide has a 1- charge, the number of bromide ions must balance the total positive charge from the cation. This is why formulas like NaBr and MgBr2 look different. ### [Cl-](/intro-chem/key-terms/cl) Cl- and Br- are both halide ions with a single negative charge, so they often show up in the same type of ionic formula problems. The main difference is the element name and symbol, not the charge pattern. If you know how chloride works, bromide follows the same balancing logic. ## On the AP Exam A quiz question might show you an ionic formula and ask you to name the anion, or it may give you Br- and ask what charge it has and how it combines with a metal ion. You use the symbol as a charge clue, then balance it against a cation to write the correct compound formula. In problem sets, that usually means checking whether one Br- is enough, or whether you need two bromide ions to match a 2+ metal ion. If you are given a reaction or formula list, Br- also helps you identify whether a compound is a bromide salt rather than elemental bromine. The fast move is always the same: read the charge, pair it, and make the total charge zero. ## Br- vs Bromine Bromine is the neutral element, Br2 in its elemental form, while Br- is the bromide ion with a negative charge. If the problem is about ionic bonding or formulas, you usually want bromide. If it is about the pure element, you want bromine. ## Key Takeaways - Br- is the bromide ion, which means bromine has gained one electron and carries a 1- charge. - In ionic compounds, bromide pairs with cations so the total charge adds up to zero. - Because Br- has only one negative charge, the formula changes depending on whether the cation is +1, +2, or another charge. - Br- is the ion form you use in formula writing, naming, and charge balancing, not the neutral element bromine. - If you can read Br- correctly, you can build or check many bromide salts without guessing. ## FAQs ### What is Br- in Intro to Chemistry? Br- is the bromide ion, a bromine atom that has gained one electron and now has a 1- charge. In Intro to Chemistry, it shows up in ionic bonding problems, especially when you are writing formulas and balancing charges. ### Is Br- the same as bromine? No. Bromine is the neutral element, while Br- is the negatively charged ion made from bromine. That charge change is what makes bromide useful in ionic compounds. ### How does Br- form an ionic compound? Br- attracts positive ions, such as Na+ or Mg2+, through electrostatic attraction. The final formula depends on electrical neutrality, so the charges must cancel out in the compound. ### Why does MgBr2 have two bromide ions? Magnesium is Mg2+, and each bromide ion is only 1-. Two Br- ions are needed to balance one Mg2+ ion. That is a direct charge-balancing move, not a random rule to memorize. ## Related Study Guides - [7.1 Ionic Bonding](/intro-chem/unit-7/1-ionic-bonding/study-guide/N1DAsggeNuxVPqdC) ## About This Document Canonical Fiveable pages are available as Markdown at the same path plus `.md`. - [llms.txt](https://fiveable.me/llms.txt): index of Fiveable's sections and URL patterns - [llms-full.txt](https://fiveable.me/llms-full.txt): complete subject and unit listing - [MCP server](https://fiveable.me/mcp): call Fiveable as tools instead of fetching pages (`https://fiveable.me/api/mcp`) - [MCP server for AP teachers](https://fiveable.me/mcp/teachers): a teacher's classes, assignments and AP-rubric grading (`https://fiveable.me/api/mcp/teacher`) ## Structured Data ```json {"@context":"https://schema.org","@graph":[{"@type":"LearningResource","@id":"https://fiveable.me/intro-chem/key-terms/br#resource","name":"Br- Bromide Ion | Intro to Chemistry","url":"https://fiveable.me/intro-chem/key-terms/br","learningResourceType":"Concept explainer","educationalLevel":"AP® / High School","about":{"@id":"https://fiveable.me/intro-chem/key-terms/br#term"},"audience":{"@type":"EducationalAudience","educationalRole":"student"},"dateModified":"2026-07-03T02:22:17.061Z","isPartOf":{"@type":"Collection","name":"Intro to Chemistry Key Terms","url":"https://fiveable.me/intro-chem/key-terms"},"author":{"@type":"Organization","@id":"https://fiveable.me/editorial#content-team","name":"Fiveable Content Team","url":"https://fiveable.me/editorial","parentOrganization":{"@id":"https://fiveable.me/#organization"},"member":[{"@type":"Person","name":"Amanda DoAmaral","sameAs":["https://www.linkedin.com/in/adoamaral"]},{"@type":"Person","name":"Becky Bahr","sameAs":["https://www.linkedin.com/in/becky-bahr-b52743132"]}]},"publisher":{"@type":"Organization","name":"Fiveable","url":"https://fiveable.me"}},{"@type":"DefinedTerm","@id":"https://fiveable.me/intro-chem/key-terms/br#term","name":"Br-","description":"Br- is the bromide ion, a bromine atom with a 1- charge. 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