Textbook Question
Explain each of the following observations:
c. The boiling point of HF is much higher than those of the other hydrogen halides.
Ch.22 - Chemistry of the Nonmetals
Chapter 22, Problem 35
Complete the exercises below. Explain each of the following observations: a. At room temperature, I₂ is a solid, Br₂ is a liquid, and Cl₂ and F₂ are both gases. b. F₂ cannot be prepared by electrolytic oxidation of aqueous F⁻ solutions. c. The halogens decrease in oxidizing power in the order F₂ > Cl₂ > Br₂ > I₂.
Verified step by step guidance1
a. The physical states of halogens at room temperature are determined by the strength of intermolecular forces. Iodine (I₂) is a solid because it has the strongest London dispersion forces due to its larger number of electrons and greater polarizability. Bromine (Br₂) is a liquid as it has moderate London dispersion forces. Chlorine (Cl₂) and fluorine (F₂) are gases because they have weaker London dispersion forces due to their smaller size and fewer electrons.
b. Fluorine (F₂) cannot be prepared by electrolytic oxidation of aqueous F⁻ solutions because fluorine is a very strong oxidizing agent. In aqueous solutions, water is more easily oxidized than fluoride ions, leading to the production of oxygen gas instead of fluorine gas. This is due to the fact that the oxidation potential of water is lower than that of fluoride ions.
c. The oxidizing power of halogens decreases in the order F₂ > Cl₂ > Br₂ > I₂ because of their electronegativity and bond dissociation energies. Fluorine is the most electronegative element, making it the strongest oxidizing agent as it readily gains electrons. As you move down the group, the electronegativity decreases and the bond dissociation energy increases, making the halogens less effective at gaining electrons and thus decreasing their oxidizing power.
To understand the trend in oxidizing power, consider the standard reduction potentials of the halogens. Fluorine has the highest reduction potential, indicating it is the most likely to gain electrons and act as an oxidizing agent. As you move down the group, the reduction potentials decrease, reflecting the decreasing oxidizing power.
The differences in physical states and chemical reactivity among the halogens can be attributed to their molecular size, electron configuration, and the resulting intermolecular forces and electronegativity. These factors collectively influence their physical properties and chemical behavior.
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
States of Matter and Molecular Interactions
The state of a substance (solid, liquid, gas) at room temperature is influenced by intermolecular forces and molecular size. Iodine (I₂) is a solid due to stronger London dispersion forces from its larger electron cloud, while bromine (Br₂) is a liquid with moderate forces. Chlorine (Cl₂) and fluorine (F₂), being smaller, have weaker forces, allowing them to exist as gases at room temperature.
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Electrolysis and Ion Stability
Electrolysis involves breaking down compounds into their elements using electricity. Fluoride ions (F⁻) are highly stable and do not easily oxidize to form fluorine gas (F₂) during electrolysis. This is due to the high electronegativity of fluorine, which makes it energetically unfavorable to remove an electron from F⁻, preventing the formation of F₂.
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Oxidizing Power of Halogens
The oxidizing power of halogens decreases down the group from fluorine to iodine. This trend is due to the increasing atomic size and decreasing electronegativity, which reduce the ability of larger halogens to attract electrons. Consequently, fluorine (F₂) is the strongest oxidizer, while iodine (I₂) is the weakest, as it is less effective at gaining electrons.
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