Question

Assign oxidation states to all of the atoms in each of the following: a. \(\mathrm{C} \mathrm{l}_{2}\) b. \(\mathrm{CoCl}_{2}\) c. \(\mathrm{CoCl}_{3}\) d. \(\mathrm{CO}_{2}\)

Short answer

The oxidation states for each compound are: a. \(\mathrm{Cl}_{2}\): Cl = 0 b. \(\mathrm{CoCl}_{2}\): Co = +2, Cl = -1 c. \(\mathrm{CoCl}_{3}\): Co = +3, Cl = -1 d. \(\mathrm{CO}_{2}\): C = +4, O = -2

Step-by-step solution

Identify element and apply rules

Since this is an elemental form of chlorine, both chlorine atoms have an oxidation state of zero, according to the first rule. b. \(\mathrm{CoCl}_{2}\)

Identify elements and apply rules

In this compound, we have cobalt (Co) and chlorine (Cl). Chlorine is more electronegative than cobalt, so it will have a negative oxidation state. Each chlorine atom has a -1 oxidation state, and since there are 2 chlorine atoms, the total negative charge is -2. To make the overall charge of the compound zero, cobalt must have a +2 oxidation state. c. \(\mathrm{CoCl}_{3}\)

Identify elements and apply rules

In this compound, we again have cobalt (Co) and chlorine (Cl). Chlorine is more electronegative and will have a -1 oxidation state. There are 3 chlorine atoms, so the total negative charge is -3. To make the overall charge of the compound zero, cobalt must have a +3 oxidation state. d. \(\mathrm{CO}_{2}\)

Identify elements and apply rules

In this compound, we have carbon (C) and oxygen (O). Oxygen is more electronegative than carbon and will have a -2 oxidation state. There are 2 oxygen atoms, so the total negative charge is -4. To make the overall charge of the compound zero, carbon must have a +4 oxidation state. To summarize the oxidation states for each compound: a. \(\mathrm{Cl}_{2}\): Cl = 0 b. \(\mathrm{CoCl}_{2}\): Co = +2, Cl = -1 c. \(\mathrm{CoCl}_{3}\): Co = +3, Cl = -1 d. \(\mathrm{CO}_{2}\): C = +4, O = -2

Key concepts

Chemical Bonding

Chemical bonding is the force that holds atoms together in compounds. The nature of chemical bonds can be explained based on electron-sharing or transfer.

There are three major types of bonds: ionic, covalent, and metallic. Ionic bonds occur when one atom donates an electron to another, creating ions with opposite charges that attract each other. In the context of the exercise, CoCl2 and CoCl3 illustrate examples where cobalt and chlorine form ionic bonds. Cobalt donates electrons to the more electronegative chlorine.

Covalent bonds, on the other hand, form when atoms share electrons. CO2 is a classic example, with carbon sharing electrons with oxygen atoms. Through this electron sharing, each atom achieves a stable electron configuration. Understanding chemical bonding is essential in determining the oxidation states in compounds because it reflects the electron distribution among the atoms involved.

Redox Reactions

Redox reactions are a type of chemical reaction that involves the exchange of electrons between two species. The term 'redox' is a shorthand for reduction-oxidation. In any redox reaction, there are two key processes occurring simultaneously: reduction, where a molecule, atom or ion gains electrons; and oxidation, where a molecule, atom or ion loses electrons.

For instance, in the assignment of oxidation states in the given textbook exercise, we are essentially examining a redox balance without an explicit chemical reaction. The rules used to assign oxidation states help visualize the theoretical transfer of electrons. For example, in CoCl2, cobalt is oxidized as it effectively loses electrons to chlorine, while chlorine is reduced. This concept also applies to CO2, where carbon would be considered as having been oxidized by oxygen. Insights into redox processes are vital in understanding the behavior of elements in chemical reactions.

Electronegativity

Electronegativity is a measure of an atom's tendency to attract and hold onto electrons. It is a dimensionless quantity, often understood on a relative scale where fluorine is assigned the highest value of 4.0.

In the exercise, electronegativity plays a crucial role in determining the oxidation states. Generally, in a bond between two different elements, the more electronegative element will attract electrons closer to itself and will hence carry a partial negative charge. For example, chlorine has a higher electronegativity than cobalt, which leads us to associate a -1 oxidation state with chlorine in both CoCl2 and CoCl3. Similarly, oxygen is more electronegative than carbon, which is why in CO2, oxygen has a -2 oxidation state. Understanding electronegativity is essential for predicting how atoms will interact in chemical bonds.