Ch.8 - Basic Concepts of Chemical Bonding

Problem 44

Chapter 8, Problem 44

The iodine monobromide molecule, IBr, has a bond lengthof 249 pm and a dipole moment of 1.21 D. (a) Which atom ofthe molecule is expected to have a negative charge?

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Identify the atoms in the IBr molecule: iodine (I) and bromine (Br).

Recall that the dipole moment is a measure of the separation of positive and negative charges in a molecule.

Understand that the dipole moment points from the positive to the negative charge.

Consider the electronegativity of the atoms: Bromine (Br) is more electronegative than iodine (I).

Conclude that the more electronegative atom, bromine (Br), will have a partial negative charge, while iodine (I) will have a partial positive charge.

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Key Concepts

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

Electronegativity

Electronegativity is a measure of an atom's ability to attract and hold onto electrons in a chemical bond. In the case of IBr, iodine (I) is less electronegative than bromine (Br), meaning that Br will attract the shared electrons more strongly, leading to a partial negative charge on the bromine atom.

Dipole Moment

The dipole moment is a vector quantity that represents 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 IBr, the dipole moment of 1.21 D indicates that there is an uneven distribution of electron density, confirming that one atom carries a partial negative charge.

Bond Polarity

Bond polarity refers to the distribution of electrical charge over the atoms joined by the bond. In IBr, the difference in electronegativity between bromine and iodine results in a polar covalent bond, where bromine becomes partially negative and iodine partially positive, leading to the overall dipole moment observed in the molecule.

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Textbook Question

Arrange the bonds in each of the following sets in order of increasing polarity: (c) C—S, B—F, N—O.

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Textbook Question

(a) From the data in Table 8.2, calculate the effective charges on the H atom of the HBr molecule in units of the electronic charge, e.

(b) If you were to put HBr under very high pressure, so its bond length decreased significantly, would its dipole moment increase, decrease, or stay the same, if you assume that the effective charges on the atoms do not change?

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Textbook Question

In the following pairs of binary compounds, determine which one is a molecular substance and which one is an ionic substance. Use the appropriate naming convention (for ionic or molecular substances) to assign a name to each compound: (a) SiF₄ and LaF₃ (for ionic or molecular substances) to assign a name to each compound: (b) FeCl₂ and ReCl₆(c) PbCl₄ and RbCl.