Final answer:
In chemistry, brackets are used in chemical formulas to indicate the physical states of substances, show polyatomic groups attached to a carbon atom, and represent the charges of polyatomic ions. It helps clarify molecular structures, physical states, and charge distributions.
Step-by-step explanation:
Brackets are placed around reagents in chemical formulas and equations for various reasons. When dealing with condensed structural formulas, parentheses are used to indicate that a group of atoms is attached to the adjacent carbon atom. This helps clarify the molecular structure of a compound.
In chemical reactions, it is important to know the physical states of the reactants and products. To convey this information, symbols such as (s) for solid, (l) for liquid, (g) for gas, and (aq) for an aqueous solution are included in parentheses right after the respective chemical formula. Additionally, when illustrating chemical equations, coefficients are used to indicate the number of molecules, and subscripts are part of the formulas to show the number of atoms of each element within the molecule.
For polyatomic ions and complex species, large brackets are employed with the charge written as superscript outside the brackets. This conveys the entire ion's charge, distinguishing it from the surrounding formula. For example, square brackets are used when depicting the structure and charge of a complex such as a borohydride ion, where the boron atom has a formal charge and the overall ion has a net charge. This ensures clarity in the representation of the molecule or ion in question.