Chemical compounds are categorized by the forces that hold their constituent atoms together: ionic bonds and covalent bonds. Ionic bonds form through the transfer of electrons from a metallic element to a nonmetallic element, resulting in the formation of oppositely charged ions. Covalent bonds, in contrast, form when two nonmetallic atoms share electrons between them to achieve a stable configuration.
The Overall Classification of \(\text{NaBrO}_3\)
Sodium bromate, represented by the chemical formula \(\text{NaBrO}_3\), is formally classified as an ionic compound. \(\text{NaBrO}_3\) is a salt composed of a positively charged metal ion and a negatively charged polyatomic ion. The compound separates into the sodium cation (\(\text{Na}^+\)) and the bromate anion (\(\text{BrO}_3^-\)). In instances where a compound contains both types of bonding, the overall classification is determined by the dominant bond that forms the compound’s structure. The strong electrostatic attraction between the metal cation and the polyatomic anion is considered the defining structural force.
The Ionic Interaction Between Sodium and Bromate
The formation of the ionic bond in sodium bromate is initiated by the transfer of an electron from the sodium atom. Sodium (\(\text{Na}\)) is an alkali metal, meaning it has a single valence electron in its outermost shell. It readily loses this electron to achieve a stable, noble-gas electron configuration, forming the positively charged sodium cation (\(\text{Na}^+\)). This single electron is transferred to the entire bromate group (\(\text{BrO}_3\)), which accepts it to form the bromate anion (\(\text{BrO}_3^-\)) with a single negative charge.
Once the ions are formed, the resulting \(\text{Na}^+\) cation and \(\text{BrO}_3^-\) anion are held together by a powerful electrostatic force. This mutual attraction causes the ions to arrange themselves into a highly ordered, repeating three-dimensional structure known as a crystal lattice. Sodium bromate exists as a white crystalline solid, which is a physical manifestation of this strong ionic lattice structure. The high melting point of \(381^\circ \text{C}\) for \(\text{NaBrO}_3\) is a direct result of the large amount of energy required to break these numerous, strong electrostatic interactions.
The Internal Covalent Structure of the Bromate Ion
While the overall compound is ionic, the bromate anion (\(\text{BrO}_3^-\)) itself contains a distinctly different type of bonding. The bromate ion is classified as a polyatomic ion, meaning it is a group of nonmetallic atoms—one bromine atom and three oxygen atoms—that are chemically bonded together. These internal bonds are covalent, involving the sharing of electrons between the nonmetal atoms.
Within the \(\text{BrO}_3^-\) ion, the central bromine atom is covalently bonded to the three surrounding oxygen atoms. The bonds are formed by the mutual sharing of valence electrons, which ensures that all atoms within the ion achieve a stable electron configuration. This sharing of electrons gives the bromate ion its structural integrity, allowing it to function as a single, charged unit. The internal structure of the bromate ion is specifically a trigonal pyramidal shape. This geometry is due to the central bromine atom being bonded to the three oxygen atoms and also possessing one lone pair of non-bonding electrons. This internal covalent structure allows the \(\text{BrO}_3^-\) group to maintain a net negative charge of \(-1\) while participating in the larger ionic structure of sodium bromate.