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Mobile App Chapter 4: Problem 90
Identify the molecules with a dipole moment: (a) \(\mathrm{SF}_{4}\) (b) \(\mathrm{CF}_{4}\) (c) \(\mathrm{Cl}_{2} \mathrm{CCBr}_{2}\) (d) \(\mathrm{CH}_{3} \mathrm{Cl}\) (e) \(\mathrm{H}_{2} \mathrm{CO}\)
Short Answer
Expert verified
Molecules with dipole moments are SF4, Cl2CCBr2, CH3Cl, and H2CO.
Step by step solution
01
Analyze Molecule Structure - SF4
Determine the molecular geometry of SF4. Sulfur tetrafluoride (SF4) has a seesaw shape due to one lone pair on the sulfur atom, which is in the central position with four fluorine atoms around it. This asymmetry in spatial arrangement leads to an unequal distribution of charge and creates a dipole moment.
02
Analyze Molecule Structure - CF4
Determine the molecular geometry of CF4. Carbon tetrafluoride (CF4) has a tetrahedral structure. Since carbon and fluorine have different electronegativities and the shape is symmetric, the individual dipoles cancel out, resulting in no overall dipole moment.
03
Analyze Molecule Structure - Cl2CCBr2
Consider the arrangement of atoms in Cl2CCBr2. This molecule is symmetrical, with the same atoms on opposite sides of the central carbon atom. However, because chlorine and bromine have different electronegativities, the symmetry does not lead to cancellation of dipoles. Therefore, Cl2CCBr2 has a net dipole moment.
04
Analyze Molecule Structure - CH3Cl
Determine the molecular geometry of CH3Cl. The molecule has a tetrahedral shape but with three hydrogen atoms and one chlorine atom attached to carbon. Since the electronegativities of hydrogen and chlorine are different and the molecule is asymmetrical, CH3Cl has a net dipole moment.
05
Analyze Molecule Structure - H2CO
Determine the molecular geometry of H2CO. Formaldehyde (H2CO) has a trigonal planar structure with different atoms around the central carbon atom. The electronegativity difference between the atoms leads to an asymmetrical charge distribution and a dipole moment.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Molecular Geometry
Understanding the shape of molecules is crucial when assessing their chemical behavior, especially regarding the dipole moment. Molecular geometry refers to the three-dimensional arrangement of atoms in a molecule. Different shapes, such as linear, bent, trigonal planar, tetrahedral, and seesaw, are determined by the number of bonds and lone pairs around a central atom.
For example, the molecule SF4 has a seesaw geometry due to a lone pair on the sulfur atom. This geometry causes an unequal distribution of charge, which induces a dipole moment. In contrast, CF4 forms a symmetric tetrahedral shape where individual bond dipoles cancel each other out, leading to no overall dipole moment.
For example, the molecule SF4 has a seesaw geometry due to a lone pair on the sulfur atom. This geometry causes an unequal distribution of charge, which induces a dipole moment. In contrast, CF4 forms a symmetric tetrahedral shape where individual bond dipoles cancel each other out, leading to no overall dipole moment.
Electronegativity
Electronegativity is a measure of an atom's ability to attract and hold onto electrons. Elements vary in electronegativity, and this variation plays a significant role in the polarity of molecules. When two atoms with differing electronegativities form a bond, the more electronegative atom pulls the bonding electrons closer, generating a dipole.
The differing electronegativities of carbon and fluorine in CF4 create individual dipoles. However, due to the molecule's symmetry, these dipoles are balanced and result in a nonpolar molecule. On the other hand, in CH3Cl, chlorine’s higher electronegativity compared to hydrogen leads to a net dipole moment.
The differing electronegativities of carbon and fluorine in CF4 create individual dipoles. However, due to the molecule's symmetry, these dipoles are balanced and result in a nonpolar molecule. On the other hand, in CH3Cl, chlorine’s higher electronegativity compared to hydrogen leads to a net dipole moment.
Molecule Symmetry
Symmetry in molecules often determines whether there is a net dipole moment. A molecule is considered symmetrical if you can divide it into two identical halves in at least one way. Symmetrical molecules, like CF4 with its tetrahedral structure, tend to have no net dipole moment because the individual dipole moments of the bonds cancel each other out.
Contrastingly, molecules like Cl2CCBr2 might appear symmetrical but actually have dissimilar atoms with different electronegativities, leading to an overall dipole moment, showcasing that symmetry isn't solely a factor of spatial arrangement but also of the properties of the atoms involved.
Contrastingly, molecules like Cl2CCBr2 might appear symmetrical but actually have dissimilar atoms with different electronegativities, leading to an overall dipole moment, showcasing that symmetry isn't solely a factor of spatial arrangement but also of the properties of the atoms involved.
Spatial Arrangement of Atoms
The spatial arrangement of atoms within a molecule can influence whether dipole moments from individual bonds cancel out or result in a net dipole moment. The 3D structure, determined by the valence shell electron pair repulsion (VSEPR) theory, dictates how bonds and lone pairs are positioned around the central atom, influencing the molecule’s overall polarity.
For instance, the tetrahedral shape of CF4 allows for bond dipoles to cancel out, whereas the asymmetrical arrangement in SF4 prevents the cancellation of dipole moments, resulting in a molecule with a dipole moment.
For instance, the tetrahedral shape of CF4 allows for bond dipoles to cancel out, whereas the asymmetrical arrangement in SF4 prevents the cancellation of dipole moments, resulting in a molecule with a dipole moment.
Polarity in Molecules
Understanding Dipole Moments
Polarity in molecules is a concept that refers to the distribution of electrical charge across the molecule. It determines whether a molecule has a dipole moment, which is a measure of the separation of positive and negative charge in the molecule. Molecules with a net dipole moment are considered polar, like H2CO, due to an uneven distribution of electrons.- A molecule with identical peripheral atoms and no lone pairs on the central atom, like CF4, is nonpolar.
- A molecule with a central atom bonded to different atoms, such as H2CO, is polar.
- Even if a molecule has symmetrical shape, differences in electronegativity can result in polarity, as seen in Cl2CCBr2.
