Question

In which of the following the oxidation number of oxygen has been arranged in increasing order : (a) \(\mathrm{OF}_{2}<\mathrm{KO}_{2}<\mathrm{BaO}_{2}<\mathrm{O}_{3}\) (b) \(\mathrm{BaO}_{2}<\mathrm{KO}_{2}<\mathrm{O}_{3}<\mathrm{OF}_{2}\) (c) \(\mathrm{BaO}_{2}<\mathrm{O}_{3}<\mathrm{OF}_{2}<\mathrm{KO}_{2}\) (d) \(\mathrm{KO}_{2}<\mathrm{OF}_{2}<\mathrm{O}_{3}<\mathrm{BaO}_{2}\)

Short answer

Option (d) \text{KO}_{2}<\text{OF}_{2}<\text{O}_{3}<\text{BaO}_{2} is the correct order with the oxidation numbers of oxygen in increasing order.

Step-by-step solution

- Identify the Oxidation Numbers in Each Compound

Determine the oxidation number of oxygen in each compound given in the options. For OF2, oxygen is more electronegative than fluorine, so it gets a negative charge. However, in compounds with fluorine, oxygen has a positive oxidation state due to the higher electronegativity of fluorine. In peroxides like BaO2 and KO2, oxygen has a -1 oxidation state. In O3, which is a molecule of ozone, oxygen is in its stable form and has a 0 oxidation state.

- Arrange the Oxidation Numbers Found

Next, we arrange the oxidation numbers in increasing order. For OF2, oxygen has a +2 oxidation state. For KO2, which is a superoxide, each oxygen has a fractional oxidation state of -1/2. In BaO2, each oxygen again has a oxidation state of -1, because it's a peroxide. Lastly, in O3, oxygen has a oxidation state of 0.

- Select the Correct Order

Look for the sequence that has the oxidation numbers of oxygen in increasing order based on our findings from step 2. This is the correct order: Superoxides (-1/2) < Peroxides (-1) < Stable Oxygen (0) < Fluorides with Oxygen (+2).

Key concepts

Chemical Oxidation States

Understanding the chemical oxidation states of elements in compounds is crucial as it dictates the electron transfer during chemical reactions.

Understanding oxidation states is fundamental to grasping concepts related to redox reactions. An oxidation state, often known as an oxidation number, indicates the degree of oxidation of an atom within a molecule or ion. Think of it as a bookkeeper's tool for keeping track of electrons during chemical reactions.

Oxidation State Rules

To assign oxidation numbers, chemists use a set of rules. For instance, the oxidation state of an element in its free form, like the O2 molecule, is always zero. In binary compounds with metals, oxygen usually has an oxidation state of -2, but there are important exceptions. When bonded to elements with higher electronegativity, such as fluorine, it can adopt positive values. This isn't intuitive, as oxygen is often seen 'hogging' electrons due to its own high electronegativity. When determining oxidation states in a compound, it's also essential to remember that the sum of all oxidation numbers for a neutral compound must equal zero, and for an ion, the sum must equal the charge of the ion.

Peroxides and Superoxides

In chemistry, peroxides and superoxides are intriguing cases that break away from the typically seen oxidation number of oxygen.

Peroxides

In peroxides, such as barium peroxide (BaO2), oxygen exhibits an oxidation state of -1. This is because the oxygen atoms are linked together, each sharing an extra electron, hence the departure from the more common -2 state. Peroxides are often used as bleach and in some chemical reactions where a gentle oxidant is required.

Superoxides

Superoxides, like potassium superoxide (KO2), push the envelope even further. Each oxygen atom here has a fractional oxidation number of -1/2. Superoxides are typically strong oxidizing agents and have interesting applications. For example, KO2 is used in life support systems because it absorbs carbon dioxide and releases oxygen.Understanding the nuanced differences between these types of oxygen compounds requires careful examination of their structure and bonding. These exceptions in oxidation numbers are significant when predicting the reactivity and stability of compounds.

Electronegativity in Compounds

Electronegativity plays a determining role in the assignment of oxidation numbers in compounds. It's a measure of how strongly atoms attract bonding electrons to themselves.The electronegativity values of atoms provide insight into the nature of bonding, whether ionic or covalent, and influence the oxidation state assigned to each element in a compound.

Higher Electronegativity

In compounds, the atom with the higher electronegativity will typically have a negative oxidation state, indicating that it has gained control over more electrons. For instance, in water (H2O), oxygen is more electronegative than hydrogen and thus has an oxidation number of -2 while hydrogen has +1.

Electronegativity Anomalies

Anomalies arise when an element like oxygen, known for its high electronegativity, interacts with fluorine, which has an even higher electronegativity. In compounds such as OF2 (oxygen difluoride), oxygen's usual oxidation number of -2 is flipped, and it adopts a positive value instead. Recognizing these anomalies is important, as they can carry implications for the compound's reactivity and can be critical in predicting product formation in chemical reactions.