Bromine
Bromine (Br, atomic number 35) is a Period 4 halogen (p-block, 79.904 u). One of only two elements that are liquid at standard room temperature (298 K), alongside mercury. Serves as an essential cofactor for peroxidasin to form sulfilimine cross-link
Bromine is a chemical element on the periodic table with the atomic symbol Br, atomic number 35, and standard atomic weight 79.904 u. Classified as a Halogen within Group 17 and Period 4 (p-block), bromine possesses a ground-state electron configuration of [Ar] 3d10 4s2 4p5 distributed across 4 concentric Bohr electron shells (2 · 8 · 18 · 7) with 7 outer-shell electrons. One of only two elements that are liquid at standard room temperature (298 K), alongside mercury. Serves as an essential cofactor for peroxidasin to form sulfilimine cross-links in basement membrane collagen IV.
⚛️ Interactive Periodic Table Lab: Explore Bromine (Br, Z = 35) in the CRV Science Dynamic Periodic Table & Bohr Orbital Lab to visualize its animated 2 · 8 · 18 · 7 electron shells, simulate live phase transitions from 0 K to 6,000 K, and compare periodic heatmaps across all 118 IUPAC elements.
Atomic Structure and Periodic Trends: How Do Quantum Orbitals Define Bromine?
Electron Shell Architecture and Ground-State Configuration
A neutral atom of bromine contains 35 protons in its atomic nucleus balanced by 35 electrons occupying quantized atomic orbitals. In the Bohr-Sommerfeld and quantum-mechanical orbital models, these electrons populate 4 principal energy shells (K (n=1): 2e−, L (n=2): 8e−, M (n=3): 18e−, N (n=4): 7e−), terminating in the directional dumbbell-shaped p-orbital (azimuthal quantum number l = 1) with ground-state configuration [Ar] 3d10 4s2 4p5. Removing the most loosely bound valence electron from an isolated gaseous bromine atom requires a first ionization energy of 1,140 kJ/mol, while its tendency to attract shared bonding electrons is quantified by a Pauling electronegativity of 2.96.
Periodic Table Position and Neighboring Elements
Within the periodic table, Bromine occupies Period 4, Group 17 of the p-block (Halogens). Along Period 4, it is flanked by Selenium (Se, Z = 34) and Krypton (Kr, Z = 36). Vertically within its periodic family, Bromine shares valence orbital symmetry and homologous chemical trends with Fluorine (F), Chlorine (Cl), Iodine (I), Astatine (At). Learners can interactively compare Bromine's orbital radii, ionization energy, and Pauling electronegativity against all neighboring elements in the Dynamic Periodic Table Lab.
Physical and Thermodynamic Properties: How Does Bromine Behave Across Temperature Regimes?
Standard Phase, Melting Point, and Boiling Point Dynamics
At standard ambient temperature and pressure (298.15 K / 25 °C, 1 atm), elemental bromine exists as a dense liquid. As thermal energy increases, its crystal or molecular lattice undergoes solid-to-liquid fusion at a melting point of 265.8 K (-7.35 °C / +18.8 °F) and transitions to the vapor phase at a normal boiling point of 332 K (+58.85 °C / +137.9 °F), spanning a liquid thermodynamic range of 66.20 K. In the CRV Science Dynamic Periodic Table, dragging the live temperature slider between absolute zero (0 K) and solar-photosphere temperatures (6,000 K) dynamically tracks Bromine's state transitions in real time alongside enthalpy and entropy phase equilibria.
Quantitative Atomic and Thermodynamic Parameter Matrix
| Parameter | Quantitative Value / Formula | Physical / Quantum Basis | Comparative Context in Group 17 / Period 4 |
|---|---|---|---|
| Atomic Number & Symbol | Z = 35 (Br) | 35 nuclear protons; nuclear charge +35e | Located in Period 4, Group 17 (p-block) |
| Standard Atomic Weight | 79.904 u (g/mol) | Abundance-weighted isotopic nucleon mass | ~45 neutrons in dominant/reference mass number |
| Electron Configuration | [Ar] 3d10 4s2 4p5 | Shells: 2 · 8 · 18 · 7 (7 outer-shell e−) | Halogens valence orbital architecture |
| Electronegativity & Ionization | χ = 2.96; IE1 = 1,140 kJ/mol | Pauling bond polarity scale & first valence ionization enthalpy | Governs covalent vs. ionic bond character |
| Melting & Boiling Points | MP: 265.8 K; BP: 332 K | Cohesive lattice energy and intermolecular forces | STP (298 K) phase: LIQUID (Liquid range: 66.20 K) |
| Principal Oxidation States | -1, +1, +5 | Valence electron donation, sharing, or acceptance | Discovered / First Isolated: 1826 |
Chemical Reactivity, Bonding, and Oxidation States: How Does Bromine Form Compounds?
Characteristic Oxidation States and Coordination Chemistry
As a Group 17 p-block halogen with an ns² np⁵ valence shell (one electron short of a closed octet), it exhibits high electron affinity and oxidizing power, forming halide (−1) anions, covalent organohalogens, and interhalogen compounds. In chemical compounds, bromine exhibits characteristic oxidation states of -1, +1, +5. Depending on the electronegativity difference (Δχ) of its bonding partners—such as Oxygen (χ = 3.44), Fluorine (χ = 3.98), Chlorine (χ = 3.16), Nitrogen (χ = 3.04), Carbon (χ = 2.55), or Hydrogen (χ = 2.20)—bromine forms redox-specific oxides, halides, hydrides, or coordination complexes governed by Gibbs free energy (ΔG = ΔH − TΔS).
Nucleosynthesis, Discovery History, and Elemental Origins
First identified or isolated in 1826, Bromine carries a distinct cosmological and geochemical signature. With atomic number Z = 35 beyond the iron-56 binding-energy peak, bromine is synthesized astrophysically via neutron-capture nucleosynthesis—combining slow neutron capture (the s-process in asymptotic giant branch stars) and rapid neutron capture (the r-process in neutron-star mergers and core-collapse supernovae).
Biological Role and Scientific Applications: Why Is Bromine Important in Nature and Technology?
Biochemical Classification: Specialized / Ultra-Trace Bio-Element
In comparative biochemistry and systems physiology, Bromine is classified as Specialized / Ultra-Trace Bio-Element. Utilized by specialized lineages (e.g., diatom silica frustules, tunicate vanabins, methanogen nickel cofactors, nitrogenase). Across terrestrial and marine ecosystems, its chemical speciation interacts with enzymes, biogeochemical cycle, phytoplankton, archaea.
Key Mechanistic Functions and Technological Uses
One of only two elements that are liquid at standard room temperature (298 K), alongside mercury. Serves as an essential cofactor for peroxidasin to form sulfilimine cross-links in basement membrane collagen IV. Researchers and students can further investigate Bromine's functional role alongside all 118 elements by launching the Interactive Periodic Table & Element Detective Lab on CRV Science Learn.
Frequently Asked Scientific Questions
What is the electron configuration and valence shell structure of Bromine (Br)?
Bromine (atomic number Z = 35) has the ground-state electron configuration [Ar] 3d10 4s2 4p5, distributing its 35 electrons across 4 shells as 2 · 8 · 18 · 7. Its outermost shell contains 7 electrons, placing Bromine in Group 17, Period 4 (p-block) as a member of the Halogens. You can watch these 35 electrons orbit the nucleus in real time in the Dynamic Periodic Table Bohr Lab.
What phase of matter is Bromine at room temperature, and when does it melt or boil?
At standard room temperature (298 K / 25 °C) and 1 atm pressure, Bromine is a dense liquid. It melts at 265.8 K (-7.35 °C / +18.8 °F) and boils at 332 K (+58.85 °C / +137.9 °F). Using the 0–6,000 K temperature slider in the Interactive Periodic Table, you can observe Bromine's exact solid, liquid, and gas transitions relative to all other elements.
How does Bromine function in biochemistry, materials science, and technology?
One of only two elements that are liquid at standard room temperature (298 K), alongside mercury. Serves as an essential cofactor for peroxidasin to form sulfilimine cross-links in basement membrane collagen IV. In biological systems, it is categorized under Specialized / Ultra-Trace Bio-Element, with principal oxidation states of -1, +1, +5 and a first ionization energy of 1,140 kJ/mol.