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Ch.7 - Periodic Properties of the Elements
Chapter 7, Problem 114

(e) While it is possible to form BiF5 in the manner just described, pentahalides of bismuth are not known for the other halogens. Explain why the pentahalide might form with fluorine but not with the other halogens. How does the behavior of bismuth relate to the fact that xenon reacts with fluorine to form compounds but not with the other halogens?

Verified step by step guidance
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Step 1: Consider the size and electronegativity of fluorine compared to other halogens. Fluorine is the smallest and most electronegative halogen, which allows it to stabilize higher oxidation states in compounds like BiF5.
Step 2: Analyze the steric effects and bond strength. The small size of fluorine allows for the formation of multiple bonds around a central atom like bismuth without significant steric hindrance, unlike larger halogens.
Step 3: Discuss the bond energy. The Bi-F bond is particularly strong due to the high electronegativity of fluorine, which contributes to the stability of BiF5. Other halogens form weaker bonds with bismuth, making pentahalides less stable or impossible to form.
Step 4: Relate this to xenon chemistry. Xenon can form compounds with fluorine due to similar reasons: the ability of fluorine to stabilize high oxidation states and form strong bonds, which is not possible with other halogens.
Step 5: Conclude with the unique reactivity of fluorine. The unique properties of fluorine, such as its small size and high electronegativity, make it capable of forming stable compounds with elements that do not typically form similar compounds with other halogens.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Halogen Reactivity and Size

Fluorine is the most reactive halogen due to its small atomic size and high electronegativity, allowing it to form stable compounds with heavier elements like bismuth. In contrast, larger halogens such as chlorine, bromine, and iodine have lower reactivity and form less stable compounds with heavy elements, making pentahalides less likely.
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Oxidation States and Stability

Bismuth can exhibit a +5 oxidation state when reacting with fluorine, which stabilizes the pentahalide BiF5. However, the larger halogens do not stabilize this high oxidation state as effectively, leading to the absence of stable pentahalides with them, as they tend to favor lower oxidation states.
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Noble Gas Chemistry

Xenon can form stable compounds with fluorine due to its ability to expand its octet and accommodate higher oxidation states, similar to bismuth. However, xenon does not react with larger halogens because they do not provide the same level of stabilization for high oxidation states, limiting the formation of stable compounds.
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Related Practice
Textbook Question
Mercury in the environment can exist in oxidation states 0,+1, and +2. One major question in environmental chemistryresearch is how to best measure the oxidation state of mercuryin natural systems; this is made more complicated by thefact that mercury can be reduced or oxidized on surfaces differentlythan it would be if it were free in solution. XPS, X-rayphotoelectron spectroscopy, is a technique related to PES (seeExercise 7.111), but instead of using ultraviolet light to eject valenceelectrons, X rays are used to eject core electrons. The energiesof the core electrons are different for different oxidationstates of the element. In one set of experiments, researchersexamined mercury contamination of minerals in water. Theymeasured the XPS signals that corresponded to electrons ejectedfrom mercury's 4f orbitals at 105 eV, from an X-ray sourcethat provided 1253.6 eV of energy 11 ev = 1.602 * 10-19J2.The oxygen on the mineral surface gave emitted electron energiesat 531 eV, corresponding to the 1s orbital of oxygen.Overall the researchers concluded that oxidation states were+2 for Hg and -2 for O. (b) Compare the energies ofthe 4f electrons in mercury and the 1s electrons in oxygenfrom these data to the first ionization energies of mercuryand oxygen from the data in this chapter.
Textbook Question

When magnesium metal is burned in air (Figure 3.6), two products are produced. One is magnesium oxide, MgO. The other is the product of the reaction of Mg with molecular nitrogen, magnesium nitride. When water is added to magnesium nitride, it reacts to form magnesium oxide and ammonia gas. (c) In an experiment, a piece of magnesium ribbon is burned in air in a crucible. The mass of the mixture of MgO and magnesium nitride after burning is 0.470 g. Water is added to the crucible, further reaction occurs, and the crucible is heated to dryness until the final product is 0.486 g of MgO. What was the mass percentage of magnesium nitride in the mixture obtained after the initial burning?

Textbook Question

When magnesium metal is burned in air (Figure 3.6), two products are produced. One is magnesium oxide, MgO. The other is the product of the reaction of Mg with molecular nitrogen, magnesium nitride. When water is added to magnesium nitride, it reacts to form magnesium oxide and ammonia gas. (d) Magnesium nitride can also be formed by reaction of the metal with ammonia at high temperature. Write a balanced equation for this reaction. If a 6.3-g Mg ribbon reacts with 2.57 g NH31g2 and the reaction goes to completion, which component is the limiting reactant? What mass of H21g2 is formed in the reaction?

Textbook Question

Potassium superoxide, KO2, is often used in oxygen masks (such as those used by firefighters) because KO2 reacts with CO2 to release molecular oxygen. Experiments indicate that 2 mol of KO2(s) react with each mole of CO2(g). (a) The products of the reaction are K2CO3(s) and O2(g). Write a balanced equation for the reaction between KO2(s) and CO2(g).

Textbook Question

Potassium superoxide, KO2, is often used in oxygen masks (such as those used by firefighters) because KO2 reacts with CO2 to release molecular oxygen. Experiments indicate that 2 mol of KO2(s) react with each mole of CO2(g). (c) What mass of KO2(s) is needed to consume 18.0 g CO2(g)? What mass of O2(g) is produced during this reaction?