Question

Oxidation state of iron in \(\mathrm{Fe}(\mathrm{CO})_{4}\) is (a) \(+1\) (b) \(-1\) (c) \(+2\) (d) 0

Short answer

The oxidation state of iron in \(\mathrm{Fe}(\mathrm{CO})_{4}\) is (d) 0.

Step-by-step solution

Identify the Known Oxidation States

Carbon monoxide (CO) is a neutral molecule with an overall oxidation state of 0. However, in metal carbonyls, carbon is usually assigned an oxidation state of +1 and oxygen -2 due to the polarization of the C-O bond towards the more electronegative oxygen.

Calculate the Total Oxidation State of CO Ligands

Since CO is a neutral ligand and there are 4 CO molecules, the total oxidation state contributed by all CO ligands in \(\mathrm{Fe}(\mathrm{CO})_{4}\) is 0.

Deduce the Oxidation State of Iron

The overall charge of the complex \(\mathrm{Fe}(\mathrm{CO})_{4}\) is also 0. Therefore, the oxidation state of iron must be such that when added to the oxidation state from the CO ligands, the sum is 0. Since the CO ligands contribute 0, the oxidation state of iron must be 0.

Key concepts

Coordination Chemistry

Coordination chemistry involves the study of compounds that have a central metal atom connected to a group of surrounding molecules or ions known as ligands. These ligands can donate electron pairs to the metal atom creating a coordination complex. A real-world example of this could be hemoglobin, which is a coordination complex of iron. The iron's ability to bind with oxygen allows our blood to transport oxygen throughout our bodies.

The ligands and the central metal atom can exhibit a variety of bonding and geometric arrangements, resulting in complexes with diverse properties and reactivities. The coordination number of a metal is the number of ligand-donated bonds to the metal. In the case of the exercise example \(\mathrm{Fe}(\mathrm{CO})_{4}\), the coordination number of iron would be four, signifying that there are four carbon monoxide molecules bonded to the iron atom.

Metal Carbonyls

Metal carbonyls are coordination compounds composed of a transition metal and carbon monoxide ligands. They are fascinating due to carbon monoxide acting as a ligand that bonds to the metal atom via a metal-to-carbon covalent bond. Carbon monoxide's role as a ligand is unique because it is a neutral molecule, yet it can act as a two-electron donor through its carbon atom.

These complexes are useful in industrial applications and as reagents in the field of organic synthesis. Industrial applications include metal carbonyls as catalysts in processes like the hydroformylation reaction, an important method for producing alcohols and aldehydes from alkenes.

Importance for Catalysis

For instance, iron carbonyls are key catalysts in reactions for fuel and plastic production. Understanding the properties and principles of metal carbonyls is therefore crucial not only for chemistry students but also for their practical implications in the chemical industry.

Oxidation States Calculation

The oxidation state, often referred to as oxidation number, is a concept used in chemistry to keep track of the electrons in a molecule or coordination complex. It denotes the degree of oxidation of an atom, which can be thought of as a hypothetical charge that an atom would have if the compound was composed mostly of ions.

To calculate the oxidation state of an atom within a coordination compound, one follows a set of rules. Firstly, the oxidation states of known stable compounds such as H2, O2, and neutral molecules like CO are taken as a starting point. Next, one must consider the charge of the molecule and how the ligands, like CO in metal carbonyls, affect the central atom's electron count.

Applying Rules to Metal Carbonyls

Applying these rules to our metal carbonyl exercise, since the CO ligands are neutral and the entire compound doesn't carry a charge, the iron atom's oxidation state must balance out the total charge to zero. Hence, for \(\mathrm{Fe}(\mathrm{CO})_{4}\), the iron has an oxidation state of 0, as the carbon monoxide ligands do not alter this balance. Understanding these calculations is essential for students of chemistry in predicting the reactivity and stability of compounds.