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Ch.9 - Molecular Geometry and Bonding Theories
Chapter 9, Problem 39c

(c) Does the molecule BF2Cl have a dipole moment?

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<insert step 1> Identify the molecular geometry of BF2Cl. Boron trifluoride (BF3) is trigonal planar, but replacing one fluorine with chlorine may alter the symmetry.>
<insert step 2> Determine the electronegativity of each atom: Boron (B), Fluorine (F), and Chlorine (Cl). Fluorine is more electronegative than chlorine.>
<insert step 3> Analyze the symmetry of the molecule. In a trigonal planar molecule, if all surrounding atoms are the same, the dipoles cancel out. However, BF2Cl has different atoms.>
<insert step 4> Consider the direction of the dipole moments. The B-F bonds will have dipoles pointing towards the fluorine atoms, and the B-Cl bond will have a dipole pointing towards the chlorine atom.>
<insert step 5> Evaluate if the dipoles cancel out. Due to the difference in electronegativity and the asymmetry introduced by the chlorine atom, the dipoles do not cancel completely, resulting in a net dipole moment.>

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Key Concepts

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

Molecular Geometry

Molecular geometry refers to the three-dimensional arrangement of atoms within a molecule. The shape of a molecule is determined by the positions of its atoms and the presence of lone pairs of electrons, which can influence bond angles and overall symmetry. Understanding the geometry of BF2Cl is essential to assess whether the molecule is polar or nonpolar.
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Polarity and Dipole Moment

Polarity in molecules arises from differences in electronegativity between bonded atoms, leading to uneven distribution of electron density. A dipole moment is a vector quantity that measures the separation of positive and negative charges in a molecule. If a molecule has polar bonds and an asymmetrical shape, it will have a net dipole moment, indicating polarity.
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Symmetry in Molecules

Symmetry plays a crucial role in determining the overall polarity of a molecule. A symmetrical molecule, even with polar bonds, may have a dipole moment of zero due to the cancellation of individual bond dipoles. Analyzing the symmetry of BF2Cl helps in concluding whether the dipole moments of its bonds cancel out or contribute to a net dipole moment.
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