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Chapter 9: Problem 39

(a) Is the molecule \(\mathrm{BF}_{3}\) polar or nonpolar? (b) If you react \(\mathrm{BF}_{3}\) to make the ion \(\mathrm{BF}_{3}^{2-}\), is this ion planar? (c) Does the molecule \(\mathrm{BF}_{2} \mathrm{Cl}\) have a dipole moment?

Short Answer

Expert verified
(a) The molecule $\mathrm{BF}_{3}$ is nonpolar. (b) The ion $\mathrm{BF}_{3}^{2-}$ is not planar, as it has a tetrahedral electron domain geometry. (c) The molecule $\mathrm{BF}_{2}\mathrm{Cl}$ has a dipole moment.

Step by step solution

01

1. Determine the geometry of BF3

To determine whether BF3 is polar or nonpolar, we first need to establish its molecular geometry. This can be done by using the VSEPR (Valence Shell Electron Pair Repulsion) theory. In this case, boron is the central atom surrounded by three fluorine atoms. Boron has 3 valence electrons, while fluorine has 7 valence electrons. Thus, the BF3 molecule has 3 pairs of bonding electron domains. The molecular geometry of BF3 is trigonal planar, resulting in a 120-degree bond angle.
02

2. Identify electronegativity and polarity of BF3

Now we look at the electronegativity of the atoms in the BF3 molecule. Fluorine is among the most electronegative elements (electronegativity of 3.98), while boron has a lower electronegativity value (2.04). Despite this difference in electronegativity, the BF3 molecule has equal distribution of electron density due to its symmetric trigonal planar structure. Therefore, any individual bond dipoles will cancel each other out. This makes the molecule nonpolar. (a) The molecule BF3 is nonpolar.
03

3. Determine the geometry of BF3^2- ion

The ion BF3^2- indicates that the BF3 molecule now has an additional two electrons. Adding two extra electrons to the existing 3 pairs of bonding electron domains will provide us with 4 pairs of electron domains. With four bonded electron pairs, the molecule will assume a tetrahedral electron domain geometry. However, the question asks whether the ion is planar, not whether it is tetrahedral. (b) The ion BF3^2- is not planar, as it has a tetrahedral electron domain geometry.
04

4. Determine the geometry of BF2Cl molecule

For BF2Cl, boron remains the central atom with one fluorine atom replaced by a chlorine atom. The molecule has three pairs of bonding electron domains similar to BF3. Therefore, its molecular geometry continues to be trigonal planar.
05

5. Identify electronegativity and dipole moment in BF2Cl

In the BF2Cl molecule, fluorine has the highest electronegativity (3.98), followed by chlorine (3.16) and boron (2.04). The bond dipoles of boron-fluorine and boron-chlorine will not cancel out each other due to the difference in electronegativity between fluorine and chlorine. This will give rise to a net dipole moment in the molecule. (c) The molecule BF2Cl has a dipole moment.

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Most popular questions from this chapter

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