- The ion contains one chromium atom and four oxygen atoms, forming the basis \(CrO_4\).
- It has two extra electrons, resulting in a net negative charge of 2-, written as a superscript.
- The correct chemical representation is \(CrO_4^{2-}\).
- Thus, the final answer is \(\boxed{CrO_4^{2-}}\).
Explanation
- Analyzing the Composition of the Chromate Ion
The chromate ion is a polyatomic ion commonly encountered in chemistry. We are given the composition of this ion: it consists of one chromium atom (Cr) and four oxygen atoms (O). Furthermore, it possesses two extra electrons, which assigns a net charge of 2- to the entire ion. To represent this as a chemical formula, we place the element symbols next to each other, use subscripts to denote the number of atoms, and indicate the net charge as a superscript at the end.
- Constructing the Chemical Formula
According to the conventions of chemical notation, when an ion is composed of specific atoms, the number of each atom is indicated by a subscript following the element's symbol. Since the ion has one chromium atom, we write 'Cr'. Since it has four oxygen atoms, we write 'O_4'. Combining these gives 'CrO_4'. The ionic charge is then added as a superscript at the end of the formula. Because there are two extra electrons, the ion carries a negative charge of 2, denoted as '2-'. Putting this together, the chemical formula is \(CrO_4^{2-}\).
- Selecting the Correct Formula
Comparing our constructed formula, \(CrO_4^{2-}\), with the provided options:
- \(Cr_4O^{2-}\) suggests four chromium atoms and one oxygen atom, which is incorrect.
- \(CrO_4^{2+}\) suggests a positive charge of 2+, whereas the ion has two extra electrons (a negative charge), which is incorrect.
- \(CrO_4^{2-}\) matches our construction exactly.
Therefore, the correct formula is \(CrO_4^{2-}\).
Examples
The concept of chemical formulas is vital in laboratory settings and industrial chemistry. For example, when balancing chemical equations or preparing solutions, knowing the precise formula of an ion—like the chromate ion used in pigment manufacturing or metal finishing—ensures that the stoichiometry of a reaction is correct. Correctly identifying formulas helps prevent errors that could affect the safety, yield, or quality of chemical processes.