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Ch.8 - Basic Concepts of Chemical Bonding
Chapter 8, Problem 89c

(c) The measured dipole moment of BrCl is 0.57 D. If you assume the bond length in BrCl is the sum of the atomic radii, what are the partial charges on the atoms in BrCl using the experimental dipole moment?

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Identify the formula for dipole moment: \( \mu = q \times d \), where \( \mu \) is the dipole moment, \( q \) is the partial charge, and \( d \) is the bond length.
Convert the dipole moment from Debye to Coulomb-meters if necessary. Note that 1 D = 3.33564 \times 10^{-30} \text{ C}\cdot\text{m}.
Estimate the bond length \( d \) by adding the atomic radii of Br and Cl. Use a periodic table or a reliable source to find these values.
Rearrange the dipole moment formula to solve for the partial charge \( q \): \( q = \frac{\mu}{d} \).
Substitute the values of \( \mu \) and \( d \) into the equation to calculate the partial charge \( q \).

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Key Concepts

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

Dipole Moment

The dipole moment is a vector quantity that measures the separation of positive and negative charges in a molecule. It is calculated as the product of the charge and the distance between the charges. In the case of BrCl, the dipole moment indicates the polarity of the bond, with a value of 0.57 D suggesting a significant difference in electronegativity between bromine and chlorine.
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Partial Charges

Partial charges arise in polar covalent bonds when electrons are not shared equally between atoms due to differences in electronegativity. In BrCl, the chlorine atom, being more electronegative, will attract the shared electrons more strongly, resulting in a partial negative charge (δ-) on Cl and a partial positive charge (δ+) on Br. These charges can be calculated using the dipole moment and the bond length.
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Bond Length and Atomic Radii

The bond length in a diatomic molecule like BrCl can be estimated by summing the atomic radii of the two atoms involved. The atomic radius is a measure of the size of an atom, typically defined as the distance from the nucleus to the outermost electron shell. For BrCl, using the atomic radii allows for an approximation of the distance over which the dipole moment acts, facilitating the calculation of partial charges.
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Related Practice
Textbook Question

Consider the collection of nonmetallic elements O, P, Te, I, and B. (b) Which two would form the longest single bond?

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Textbook Question

The substance chlorine monoxide, ClO(g), is important in atmospheric processes that lead to depletion of the ozone layer. The ClO molecule has an experimental dipole moment of 1.24 D, and the Cl — O bond length is 160 pm. (b) Based on the electronegativities of the elements, which atom would you expect to have a partial negative charge in the ClO molecule?

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Textbook Question

(b) Using these partial charges and the atomic radii given in Figure 7.8, estimate the dipole moment of the molecule.

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Textbook Question

A major challenge in implementing the 'hydrogen economy' is finding a safe, lightweight, and compact way of storing hydrogen for use as a fuel. The hydrides of light metals are attractive for hydrogen storage because they can store a high weight percentage of hydrogen in a small volume. For example, NaAlH4 can release 5.6% of its mass as H2 upon decomposing to NaH(s), Al(s), and H2(g). NaAlH4 possesses both covalent bonds, which hold polyatomic anions together, and ionic bonds. (b) Which element in NaAlH4 is the most electronegative? Which one is the least electronegative? Which element in NaAlH4 is the least electronegative?

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Textbook Question

A major challenge in implementing the 'hydrogen economy' is finding a safe, lightweight, and compact way of storing hydrogen for use as a fuel. The hydrides of light metals are attractive for hydrogen storage because they can store a high weight percentage of hydrogen in a small volume. For example, NaAlH4 can release 5.6% of its mass as H2 upon decomposing to NaH(s), Al(s), and H2(g). NaAlH4 possesses both covalent bonds, which hold polyatomic anions together, and ionic bonds. (c) Based on electronegativity differences, predict the identity of the polyatomic anion. Draw a Lewis structure for this ion.

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Textbook Question

A major challenge in implementing the 'hydrogen economy' is finding a safe, lightweight, and compact way of storing hydrogen for use as a fuel. The hydrides of light metals are attractive for hydrogen storage because they can store a high weight percentage of hydrogen in a small volume. For example, NaAlH4 can release 5.6% of its mass as H2 upon decomposing to NaH(s), Al(s), and H2(g). NaAlH4 possesses both covalent bonds, which hold polyatomic anions together, and ionic bonds. (d) What is the formal charge on hydrogen in the polyatomic ion?

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