Problem 97 - Chemistry: The Central Science in SI Units, Global Edition

Question

Which of the following chemical equations is connected to the definitions of (a) the first ionization energy of oxygen, (b) the second ionization energy of ox ygen, and (c) the electron affinity of oxygen? (i) \(\mathrm{O}(g)+\mathrm{e}^{-} \longrightarrow \mathrm{O}^{-}(g)\) (ii) \(\mathrm{O}(g) \longrightarrow \mathrm{O}^{+}(g)+\mathrm{e}^{-}\) (iii) \(\mathrm{O}(g)+2 \mathrm{e}^{-} \longrightarrow \mathrm{O}^{2-}(g)\) (iv) \(\mathrm{O}(g) \longrightarrow \mathrm{O}^{2+}(g)+2 \mathrm{e}^{-}\) \((\mathbf{v}) \mathrm{O}^{+}(g) \longrightarrow \mathrm{O}^{2+}(g)+\mathrm{e}^{-}\)

Step-by-Step Solution

Answer

(a) The first ionization energy of oxygen is represented by equation (ii): \(\mathrm{O}(g) \longrightarrow \mathrm{O}^{+}(g)+\mathrm{e}^{-}\) (b) The second ionization energy of oxygen is represented by equation (v): \(\mathrm{O}^{+}(g) \longrightarrow \mathrm{O}^{2+}(g)+\mathrm{e}^{-}\) (c) The electron affinity of oxygen is represented by equation (i): \(\mathrm{O}(g)+\mathrm{e}^{-} \longrightarrow \mathrm{O}^{-}(g)\)

Step 1: Identify the First Ionization Energy Equation

Look for the equation where an oxygen atom loses one electron to form a positive ion: Ο(g) → Ο^+(g) + e^− This can be found in equation (ii).

Step 2: Identify the Second Ionization Energy Equation

Look for the equation where an oxygen ion with a charge of +1 loses another electron to form a positive ion with a charge of +2: Ο^+(g) → Ο^2+(g) + e^− This is equation (v).

Step 3: Identify the Electron Affinity Equation

Find the equation where an oxygen atom gains one electron to form a negative ion: Ο(g) + e^− → Ο^−(g) This can be found in equation (i). Now that we have identified the equations for each case, we can state our final answers. (a) The first ionization energy of oxygen is represented by equation (ii): \(\mathrm{O}(g) \longrightarrow \mathrm{O}^{+}(g)+\mathrm{e}^{-}\) (b) The second ionization energy of oxygen is represented by equation (v): \(\mathrm{O}^{+}(g) \longrightarrow \mathrm{O}^{2+}(g)+\mathrm{e}^{-}\) (c) The electron affinity of oxygen is represented by equation (i): \(\mathrm{O}(g)+\mathrm{e}^{-} \longrightarrow \mathrm{O}^{-}(g)\)

Key Concepts

Electron Affinity

Electron affinity is an essential concept in chemistry that describes an atom's ability to attract and hold onto an extra electron. When a neutral atom in the gas phase gains an electron, it forms a negative ion. This process releases energy, which is known as electron affinity. In the exercise, the electron affinity of oxygen is shown by equation (i):

• \( \mathrm{O}(g)+\mathrm{e}^{-} \longrightarrow \mathrm{O}^{-}(g) \)

This equation represents the process where an oxygen atom in the gaseous state captures an electron to become an oxide ion \( (\mathrm{O}^{-}) \).

**Why is Electron Affinity Important?**

• It helps understand how atoms form negative ions and participate in ionic bonding.
• An element with a high electron affinity tends to gain electrons easily and form anions.

Analyzing electron affinities across the periodic table reveals a trend: generally, electron affinity increases across a period from left to right. Oxygen has a relatively high electron affinity, which is why it readily participates in reactions involving electron capture.

Chemical Equations

Chemical equations provide a symbolic representation of chemical reactions, showcasing the conversion of reactants to products. They offer a concise way to convey the chemical changes occurring in a process. A complete chemical equation includes both reactants and products, with their respective states indicated and balanced in terms of atoms to conserve mass.

In the original exercise, various chemical equations are presented, and each describes a different process involving the oxygen atom.

• Equation \((\mathrm{i})\) shows oxygen gaining an electron: \( \mathrm{O}(g)+\mathrm{e}^{-} \rightarrow \mathrm{O}^{-}(g) \)
• Equation \((\mathrm{ii})\) depicts oxygen losing an electron, showing its first ionization: \( \mathrm{O}(g) \rightarrow \mathrm{O}^{+}(g)+\mathrm{e}^{-} \)
• Equation \((\mathrm{v})\) illustrates further ionization: \( \mathrm{O}^{+}(g) \rightarrow \mathrm{O}^{2+}(g)+\mathrm{e}^{-} \)

**Balancing Chemical Equations**Ensuring chemical equations are balanced is crucial. This means having equal numbers of each type of atom on both sides of the equation. For instance, when writing the electron affinity equation, the oxygen atom on the reactant side must also appear on the product side to reflect quantity and type integrity. Balancing is necessary to accurately demonstrate conservation of mass and uphold the Law of Conservation of Matter.

Oxygen Chemistry

Oxygen is a vital element that plays a crucial role in a variety of chemical processes. Understanding its behavior in reactions, such as ionization and electron gain, is fundamental for many scientific fields. In chemistry, oxygen can form different ions, such as \( \mathrm{O}^{-} \), \( \mathrm{O}^{+} \), and \( \mathrm{O}^{2+} \), depending on the chemical environment and the process it undergoes.

**Oxygen's Role in Ionic Reactions**

• In its neutral form, oxygen can attract electrons, forming negatively charged ions.
• When it loses electrons, it becomes a positively charged ion, either \( \mathrm{O}^{+} \) or \( \mathrm{O}^{2+} \), as shown in the ionization energy equations from the exercise.

Oxygen's chemistry is not limited to these simple ionic processes. It also participates in a wide array of reactions due to its high electronegativity and ability to form stable bonds with many elements. Its chemistry is extensive, involving processes such as combustion, oxidation reactions, and serving as an essential element in the formation of acids and bases. Understanding oxygen chemistry is crucial for anyone studying chemical reactions, environmental science, or biological systems.