Question

Chlorine reacts with oxygen to form \(\mathrm{Cl}_{2} \mathrm{O}_{7} .\) (a) What is the name of this product (see Table 2.6 )? (b) Write a balanced equation for the formation of \(\mathrm{Cl}_{2} \mathrm{O}_{7}(l)\) from the elements. (c) Under usual conditions, \(\mathrm{Cl}_{2} \mathrm{O}_{7}\) is a colorless liquid with a boiling point of \(81^{\circ} \mathrm{C}\). Is this boiling point expected or surprising? (d) Would you expect \(\mathrm{Cl}_{2} \mathrm{O}_{7}\) to be more reactive toward \(\mathrm{H}^{+}(a q)\) or \(\mathrm{OH}^{-}(a q) ?\) Explain. (e) If the oxygen in \(\mathrm{Cl}_{2} \mathrm{O}_{7}\) is considered to have the -2 oxidation state, what is the oxidation state of the Cl? What is the electron configuration of \(\mathrm{Cl}\) in this oxidation state?

Short answer

The compound \(\mathrm{Cl}_{2} \mathrm{O}_{7}\) is called dichlorine heptoxide. The balanced equation for its formation is \(\ce{2Cl2 (g) + 7O2 (g) -> 2Cl2O7 (l)}\). Its boiling point, \(81^{\circ} \mathrm{C}\), is expected as it indicates strong interactions between molecules. Dichlorine heptoxide would be more reactive towards \(\mathrm{H}^{+}(a q)\) as it is an oxidizing agent. The oxidation state of Cl in \(\mathrm{Cl}_{2} \mathrm{O}_{7}\) is +7, and its electron configuration in this state is \(\ce{1s^2 2s^2 2p^6 3s^2 3p^0}\).

Step-by-step solution

(a) Naming the compound

According to the nomenclature rules, \(\mathrm{Cl}_{2} \mathrm{O}_{7}\) is called dichlorine heptoxide.

(b) Balanced equation

To write a balanced equation for the formation of \(\mathrm{Cl}_{2} \mathrm{O}_{7}(l)\) from the elements, we have: \[ \ce{2Cl2 (g) + 7O2 (g) -> 2Cl2O7 (l)} \]

(c) Boiling point analysis

The boiling point of \(\mathrm{Cl}_{2} \mathrm{O}_{7}\) is given as \(81^{\circ} \mathrm{C}\). It is intermediate between the boiling points of oxygen (\(-183^{\circ} \mathrm{C}\)) and chlorine (\(-34^{\circ} \mathrm{C}\)). Since both oxygen and chlorine have lower boiling points than dichlorine heptoxide, it indicates strong interactions between \(\mathrm{Cl}_{2} \mathrm{O}_{7}\) molecules, which can be considered as expected for a covalent molecular compound.

(d) Reactivity analysis

\(\mathrm{Cl}_{2} \mathrm{O}_{7}\) has a high content of oxygen, so it can be expected to be an oxidizing agent. These agents generally react more easily with \(\mathrm{H}^{+}(a q)\) because they tend to reduce themselves by gaining electrons to form oxygen gas, water, or an oxyanion. On the other hand, \(\mathrm{OH}^{-}(a q)\) is a stronger base, which promotes reduction reactions. Therefore, \(\mathrm{Cl}_{2} \mathrm{O}_{7}\) would be more reactive towards \(\mathrm{H}^{+}(a q)\).

(e) Oxidation state and electron configuration

Knowing that the oxygen has the oxidation state -2, we can calculate the oxidation state of Cl. Let x be the oxidation state of chlorine (\(\mathrm{Cl}\)), then: \(2x + 7(-2) = 0\) Solving for x, we get: \(x = +7\) So, the oxidation state of chlorine in \(\mathrm{Cl}_{2} \mathrm{O}_{7}\) is +7. In its ground state, the electron configuration of chlorine is: \[ \ce{1s^2 2s^2 2p^6 3s^2 3p^5} \] When Cl is in the +7 oxidation state, it loses seven electrons, and its electron configuration would be: \[ \ce{1s^2 2s^2 2p^6 3s^2 3p^0} \]

Key concepts

Chemical Nomenclature

The naming of chemical compounds, like dichlorine heptoxide, follows specific rules to ensure consistent communication among scientists and students worldwide. Dichlorine heptoxide is composed of two chlorine (Cl) atoms and seven oxygen (O) atoms. The prefix 'di-' indicates two chlorine atoms, and 'hepta-' means seven, which corresponds to the number of oxygen atoms. 'Oxide' signifies the presence of oxygen in the compound. The correct and systematic naming of compounds aids in avoiding confusion, as many chemicals have common names and various synthesis methods.

The IUPAC (International Union of Pure and Applied Chemistry) nomenclature is widely followed for naming compounds and it provides a standard approach to naming chemical substances based on their composition and structure. This approach not only facilitates accurate communication but also provides insights into the potential properties and reactivity of the compounds.

Balancing Chemical Equations

The process of writing a balanced chemical equation is fundamental to understanding chemical reactions. It follows the law of conservation of mass, which states that mass can neither be created nor destroyed in a chemical reaction. Thus, the number of atoms for each element must be the same on both the reactants and products side of a reaction. Balancing the formation reaction of dichlorine heptoxide from elemental chlorine and oxygen:
\[ \ce{2Cl2 (g) + 7O2 (g) -> 2Cl2O7 (l)} \]
ensures that there are equal numbers of each kind of atom before and after the reaction. This process involves trial and error until you achieve a balance. Learning to balance equations is essential for conducting experiments, predicting product quantities, and understanding the stoichiometry of reactions—the quantitative relationship between reactants and products in a chemical reaction.

Boiling Point Analysis

The boiling point of a substance is the temperature at which its vapor pressure equals the atmospheric pressure, allowing it to transition from the liquid phase to the gaseous phase. Analyzing the boiling point can provide insights into the molecular interactions present within a compound. Dichlorine heptoxide has a boiling point of \(81^\circ \text{C}\), which is surprisingly high compared to its constituent elements, chlorine and oxygen, suggesting stronger intermolecular forces than in the diatomic molecules of these elements alone.

In a molecular compound like dichlorine heptoxide, intermolecular forces such as London dispersion forces, dipole-dipole interactions, and possibly hydrogen bonding (if H is present) are responsible for maintaining the structure in a liquid state. A higher boiling point indicates stronger intermolecular forces and greater interactions among molecules. Understanding boiling points can help predict physical properties and the conditions required for a chemical reaction or a substance's use.

Reactivity Towards Acids and Bases

A chemical's reactivity towards acids and bases depends on its molecular structure and the presence of certain functional groups. Dichlorine heptoxide's molecular architecture makes it more reactive towards hydronium ions (\(\mathrm{H}^{+}(aq)\)) rather than hydroxide ions (\(\mathrm{OH}^{-}(aq)\)). This behavior can be attributed to dichlorine heptoxide being a strong oxidizing agent; it has a high affinity for electrons, thus preferring to engage with species that can donate electrons, like the hydronium ion. This preference also reflects on the compound's behavior in oxidative reactions, where dichlorine heptoxide can facilitate the transfer of electrons and drive oxidation processes forward. The understanding of a compound's reactivity with acids and bases is crucial for predicting the outcomes of chemical reactions, especially in synthetic and analytical chemistry.

Oxidation States and Electron Configurations

The oxidation state of an element in a compound is an indicator of the degree of oxidation or reduction of that element within a molecular context. It is a conceptual charge that helps in understanding electron transfer during chemical reactions. In the case of \(\mathrm{Cl}_{2}\mathrm{O}_{7}\), considering oxygen as having an oxidation state of -2, each chlorine must have an oxidation state of +7 to satisfy the zero overall charge of the molecule. An element's oxidation state influences its electron configuration.

The ground state electron configuration of a chlorine atom is:\[ \ce{1s^2 2s^2 2p^6 3s^2 3p^5} \]
As chlorine achieves a +7 oxidation state in dichlorine heptoxide, it loses seven electrons, resulting in the electron configuration:\[ \ce{1s^2 2s^2 2p^6 3s^2 3p^0} \]
This change in electron configuration significantly alters the reactivity and chemical properties of chlorine, demonstrating the significance of understanding electron distributions in predicting and explaining the chemical behavior of elements.