In the complex ion, \(\left[\mathrm{Cr}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{2}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}\right]^{-}\), the oxidation number of \(\mathrm{Cr}\) is: (a) \(+1\) (b) \(+2\) (c) \(+3\) (d) \(+4\)

Coordination chemistry is a branch of inorganic chemistry that deals with the structure, properties, and reactions of coordination compounds, which consist of a central metal atom or ion surrounded by molecules or anions, termed ligands. In the complex ion \(\left[\mathrm{Cr}\left(\mathrm{C}_{2}\mathrm{O}_{4}\right)_{2}\left(\mathrm{H}_{2}\mathrm{O}\right)_{2}\right]^{-}\), \(\mathrm{Cr}\) is the metal center and the oxalate ions \(\left(\mathrm{C}_{2}\mathrm{O}_{4}\right)^{2-}\) along with water molecules \(\left(\mathrm{H}_{2}\mathrm{O}\right)\) act as ligands.

These ligands coordinate to the metal via donor atoms, such as oxygen in the case of water and oxalate, to form a coordination sphere. The number of ligands attached to the central metal ion is determined by the metal's coordination number, which in turn influences the geometry of the complex. Understanding how the ligands affect the central metal ion, including its oxidation state, is a crucial aspect of coordination chemistry.

In the educational content, breaking down each ligand's contribution helps students determine the oxidation state of the metal, providing a foundation for further understanding of how these complex ions behave chemically.

Redox reactions, or reduction-oxidation reactions, involve the transfer of electrons between chemical species. The substance that loses electrons is oxidized, while the substance that gains electrons is reduced. Each atom in a molecule has an oxidation number that helps chemists keep track of electron transfer.

In the context of the complex ion presented in the exercise, deducing the oxidation number of chromium leads to an understanding of the redox behavior of the complex. By identifying the overall charge of the complex and the individual charges of the ligands, we can calculate the oxidation state of the metal. This oxidation state can potentially change in redox reactions where the complex is involved, underlining the importance of recognizing an ion’s oxidation number for predicting chemical reactivity and the outcomes of redox processes.

When writing educational material, illustrating redox changes step-by-step, including how to balance redox reactions, is essential for fostering student comprehension.

Chemical bonding pertains to the force that holds atoms together within molecules or compounds. There are several types of chemical bonds, including ionic, covalent, and metallic bonds, as well as more complex interactions like those in coordination compounds.

In coordination compounds, the central metal ion and surrounding ligands are held together through coordinate covalent bonds. These involve shared pairs of electrons where the contributing atom of the electron pair comes solely from the ligand. In the complex \(\left[\mathrm{Cr}\left(\mathrm{C}_{2}\mathrm{O}_{4}\right)_{2}\left(\mathrm{H}_{2}\mathrm{O}\right)_{2}\right]^{-}\), the oxalate ions and water molecules form coordinate covalent bonds with the chromium ion.

Presenting chemical bonding concepts with clarity and context is crucial when educating students. For example, explaining the role of electrons in bond formation, the different types of bonds, and their relative strengths leads to a more comprehensive grasp of not only the structure but also the stability and reactivity of various compounds, including complex ions.