The vast majority of nonmetal elements exist as either a gas or a solid when held under standard room temperature conditions. There is only one known exception to this rule, which is the element Bromine. This unique property makes it one of only two elements on the entire periodic table, alongside the metal mercury, to be a liquid at room temperature.
Identifying Bromine
Bromine is a heavy, reddish-brown liquid with an intense, penetrating odor. This element belongs to the Halogen group, Group 17, of the periodic table, placing it chemically between chlorine and iodine.
The liquid is highly volatile, meaning it readily evaporates to form a similarly colored vapor at room temperature. Both the liquid and its vapor are corrosive and toxic, presenting a serious hazard upon skin contact or inhalation. Due to the noxious nature of the fumes, elemental Bromine must be handled with extreme caution and stored in sealed containers within well-ventilated areas.
Why Bromine is Liquid
The physical state of any substance depends on the strength of the forces that hold its molecules together. Bromine exists as a diatomic molecule (Br2), and because its atoms share electrons evenly, it is considered a non-polar molecule. The only type of attraction between these non-polar molecules are weak, temporary forces known as London Dispersion Forces (LDFs).
LDFs arise from random, momentary shifts in electron distribution around the molecule, creating temporary positive and negative ends that attract neighboring molecules. The strength of these forces increases with the size and number of electrons in a molecule. Bromine’s neighbor above it in the periodic table, chlorine (Cl2), is a gas because its smaller size results in very weak LDFs that cannot hold the molecules together as a liquid at room temperature.
Bromine’s larger size gives it significantly stronger LDFs than chlorine, which are just strong enough to hold the molecules together in a condensed liquid state. However, the element below it, iodine (I2), is even larger and has such strong LDFs that its molecules are locked into a rigid solid structure at the same temperature. Bromine occupies a unique position where its LDFs are intermediate in strength, keeping it liquid across the room temperature range.
How Bromine is Used
The high chemical reactivity of Bromine makes it a valuable component in the manufacturing of many compounds for industrial use. One of its most common applications is in the production of flame retardants, where brominated compounds are added to materials like plastics, textiles, and furniture foam. These compounds help to make the products less flammable, thereby slowing the spread of fire.
Bromine compounds are also utilized in various agricultural chemicals, often in the form of fumigants used to destroy pests in soil and stored commodities. Other applications include its use in certain photographic films through the compound silver bromide, which is sensitive to light. Bromine plays a role in water purification processes and the synthesis of numerous pharmaceutical and dye products.