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 oxygen, and (c) the electron affinity of oxygen? \((\mathbf{i})\mathrm{O}(g)+\mathrm{e}^{-} \longrightarrow \mathrm{o}^{-}(g) \quad\) \((\mathbf{ii})\mathrm{O}(g) \longrightarrow \mathrm{o}^{+}(g)+\mathrm{e}^{-}\) \((\mathbf{iii})\mathrm{O}(g)+2 \mathrm{e}^{-} \longrightarrow \mathrm{O}^{2-}(g) \quad(\mathbf{i v}) \mathrm{O}(g) \longrightarrow \mathrm{O}^{2+}(g)+2 \mathrm{e}^{-}\) \((\mathbf{v}) \mathrm{O}^{+}(g) \longrightarrow \mathrm{O}^{2+}(g)+\mathrm{e}^{-}\)

Short answer

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

Step-by-step solution

Ionization energy is the amount of energy required to remove an electron from a gaseous atom or ion. The higher the ionization energy, the more difficult it is to remove an electron. Electron affinity is the energy change that occurs when an electron is added to a gaseous atom or ion. A more positive electron affinity value indicates that the atom or ion has a stronger attraction for an additional electron. #Step 2: Match the chemical equation to the first ionization energy of oxygen#

The first ionization energy of oxygen refers to the energy required to remove the first electron from a neutral oxygen atom. We are looking for an equation that represents the removal of an electron from a gaseous oxygen atom, \(O(g)\), resulting in the formation of a positive ion, \(O^+(g)\). The matching equation is: (ii) \(O(g) \longrightarrow O^+(g) + e^{-}\) #Step 3: Match the chemical equation to the second ionization energy of oxygen#

The second ionization energy of oxygen refers to the energy required to remove an electron from an oxygen atom that has already lost one electron (i.e., from an \(O^+(g)\) ion). We need an equation that shows the removal of an electron from a gaseous \(O^+(g)\) ion, leading to the formation of an \(O^{2+}(g)\) ion. The matching equation is: (v) \(O^+(g) \longrightarrow O^{2+}(g) + e^{-}\) #Step 4: Match the chemical equation to the electron affinity of oxygen#

The electron affinity of oxygen refers to the energy change that occurs when an electron is added to a neutral oxygen atom. We are looking for an equation that represents the addition of an electron to a gaseous oxygen atom, \(O(g)\), resulting in the formation of a negative ion, \(O^-(g)\). The matching equation is: (i) \(O(g) + e^{-} \longrightarrow O^-(g)\) #Final Answers# (a) The first ionization energy of oxygen: (ii) \(O(g) \longrightarrow O^+(g) + e^{-}\) (b) The second ionization energy of oxygen: (v) \(O^+(g) \longrightarrow O^{2+}(g) + e^{-}\) (c) The electron affinity of oxygen: (i) \(O(g) + e^{-} \longrightarrow O^-(g)\)

Key concepts

First Ionization Energy

Imagine you have a single, neutral oxygen atom floating in space. The oxygen atom is content with its eight electrons until a burst of energy comes along compelling one of those electrons to leave. This is essentially what the first ionization energy refers to: it's the energy needed to strip away the first electron from an atom in its gaseous state.

For oxygen, the first ionization energy is relatively high, indicating it's quite attached to its electrons. This is because as one moves right across the periodic table, electrons are added to the same energy level while the nucleus gains protons, making its pull on the electrons stronger. In our exercise, equation (ii) \(\mathrm{O}(g) \longrightarrow \mathrm{O}^{+}(g) + \mathrm{e}^{-}\) represents this concept. The electron has been liberated, and the oxygen atom becomes a positive ion, technically known as an 'oxonium' ion.

These concepts are not just academic—they're crucial for understanding the behavior of elements and designing new materials and chemicals.

Second Ionization Energy

If the first ionization energy can be likened to peeling the first layer of an onion, the second ionization energy is like peeling the second layer—it's tougher and requires more strength. Once an oxygen atom has lost one electron and has become an \(\mathrm{O}^{+}(g)\) ion, to remove a second electron and transform it into an \(\mathrm{O}^{2+}(g)\) ion, even more energy is needed. This is known as the second ionization energy.

Equation (v) \(\mathrm{O}^{+}(g) \longrightarrow \mathrm{O}^{2+}(g) + \mathrm{e}^{-}\) depicts this process. The increase in positive charge after the first electron is removed makes the remaining electrons more strongly attracted to the nucleus, hence the higher energy requirement. Understanding the second ionization energy helps us comprehend the underlying stability of elemental configurations and predicts how an atom will react when forming compounds.

Electron Affinity

Electron affinity is sort of like a welcome party for a new electron joining an atom. It's a measure of an atom's willingness to accept an additional electron, and how much energy is released in the process. Oxygen, for instance, quite enjoys grabbing an extra electron, releasing energy as it forms a negative ion, depicted in equation (i) \(\mathrm{O}(g) + \mathrm{e}^{-} \longrightarrow \mathrm{O}^{-}(g)\).

A negative electron affinity value suggests that energy must be supplied for an electron to attach to the atom, which isn't common. For oxygen, the electron affinity is positive; the energy is released, which is akin to breathing a sigh of relief because the extra electron makes the atom more stable. This particular property is foundational for the development of ionic bonds, where atoms with different electron affinities transfer electrons to achieve greater stability.

Chemical Equations

Chemical equations are like recipes for chemists. They show us what we start with, known as reactants, and what we end up with, called products. In our oxygen example, we've looked at several of these recipes that show how oxygen behaves when it's gaining or losing electrons.

For instance, the equation \(\mathrm{O}(g) + \mathrm{e}^{-} \longrightarrow \mathrm{O}^{-}(g)\) reveals the beauty of chemical equations: the simplicity in which they summarize what happens in a reaction. Here, it's important to notice not just the reactants and products, but also the balance of charges and the conservation of matter. Chemical equations are the language through which we understand the myriad changes and interactions in the world of chemistry.