Question

In which of the following compounds carbon is in highest oxidation state? (a) \(\mathrm{CH}_{3} \mathrm{Cl}\) (b) \(\mathrm{CCl}_{4}\) (c) \(\mathrm{CHCl}_{3}\) (d) \(\mathrm{CH}_{2} \mathrm{Cl}_{2}\)

Short answer

Carbon has the highest oxidation state in compound (b) \(\mathrm{CCl}_{4}\), which is +4.

Step-by-step solution

Introduction to Oxidation States

The oxidation state of an atom in a compound represents the degree of oxidation of that element. It's the charge an atom would have if all bonds were ionic, with perfect electron transfer. For carbon compounds, every covalent bond to a more electronegative element (like chlorine) will increase the oxidation state by +1, while bonds to less electronegative elements (like hydrogen) will lower it by -1.

Calculate Oxidation States for Each Compound

Assess each compound individually: for (a) \(\mathrm{CH}_{3} \mathrm{Cl}\), carbon forms one bond with chlorine and three with hydrogen, resulting in an oxidation state of 0 + 3(-1) = -3. For (b) \(\mathrm{CCl}_{4}\), carbon forms four bonds with chlorine resulting in an oxidation state of 4(+1) = +4. For (c) \(\mathrm{CHCl}_{3}\), carbon forms one bond with hydrogen and three with chlorine resulting in an oxidation state of 1(-1) + 3(+1) = +2. For (d) \(\mathrm{CH}_{2} \mathrm{Cl}_{2}\), carbon forms two bonds with hydrogen and two with chlorine resulting in an oxidation state of 2(-1) + 2(+1) = 0.

Comparison of Oxidation States

Compare the calculated oxidation states for carbon in all four compounds to find the highest. It is clear from the calculations that carbon has the highest oxidation state in \(\mathrm{CCl}_{4}\) at +4.

Key concepts

Understanding Oxidation Numbers

Oxidation numbers, also known as oxidation states, play a pivotal role in the realm of chemistry—acting as a bookkeeping tool to track electron movement in chemical reactions. The oxidation number of an atom within a compound gives us insight into its electron gain or loss relative to the atom in its elemental state.

To determine these oxidation states, there are a set of rules: atoms in their elemental form have an oxidation number of 0. For monoatomic ions, the oxidation state is equal to the charge of the ion. In compounds, normally, the more electronegative element takes on a negative oxidation state, while the less electronegative element takes on a positive state. Hydrogen, for example, has an oxidation number of +1 when bonded to non-metals, and -1 when bonded to metals. Oxygen usually has an oxidation state of -2 in most compounds, with the exception being peroxides.

Understanding how to assign oxidation numbers to atoms in different chemical species is crucial for predicting the reactivity, especially in redox reactions where the change of these numbers reflects the transfer of electrons between species. Our exercise requires multiplying the oxidation number of an atom by the number of atoms of that element in the compound, summing these up, and comparing them to determine the highest oxidation state of carbon in the given compounds.

The Role of Electronegativity

Electronegativity is a concept that could be likened to the 'tug-of-war' strength an atom has over shared electrons in a chemical bond. It is a measure of an atom's ability to attract and hold onto the electrons within a bond. The electronegativity scale, developed by Linus Pauling, assigns fluorine—the most electronegative element—with a value of 4.0. In contrast, elements with lower electronegativity can't hold onto the shared electrons as tightly.

In organic compounds, the difference in electronegativity between bonded atoms can influence the oxidation numbers. If the bonded atom is more electronegative than carbon, it will pull electron density toward itself, increasing the oxidation number of carbon. Chlorine, for instance, is more electronegative than carbon. In a carbon-chlorine bond, chlorine will attract the shared electrons more strongly, thus making the carbon atom have a positive oxidation state.

To hone our comprehension of this in our problem, observe how each additional chlorine atom (being more electronegative than carbon) increments the oxidation number of the carbon by +1, progressively elevating the carbon to a higher oxidation state.

Properties of Carbon Compounds

Carbon compounds, or organic compounds, form the backbone of biochemistry and organic chemistry. The tetrahedral nature of carbon, with its four valence electrons, makes it a versatile element capable of forming single, double, and triple bonds with a variety of other elements and chains of itself. This attribute leads to the formation of a diverse array of structures, ranging from simple hydrocarbons to complex biomolecules.

When evaluating the oxidation state of carbon in these compounds, it is imperative to consider the type and number of bonds carbon forms. A single bond to a hydrogen atom will impart a negative effect on the carbon's oxidation state, while a single bond to a more electronegative atom like oxygen or chlorine will increase it. In our exercise, the varying combinations of bonds to hydrogen and chlorine result in different oxidation states for carbon. This knowledge of carbon's bonding and its interplay with electronegativity is crucial for predicting chemical behaviour and understanding molecular reactivity in organic chemistry.

The ability to discern the oxidation states in carbon compounds vis-à-vis their structure is a valuable skill, as illustrated in the textbook exercise, leading to insights into their chemical properties and tendencies.