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Chapter 9: Problem 57

(a) Draw Lewis structures for ethane \(\left(\mathrm{C}_{2} \mathrm{H}_{6}\right),\) ethylene \(\left(\mathrm{C}_{2} \mathrm{H}_{4}\right),\) and acetylene \(\left(\mathrm{C}_{2} \mathrm{H}_{2}\right)\) (b) What is the hybridization of the carbon atoms in each molecule? (c) Predict which molecules, if any, are planar. (d) How many \(\sigma\) and \(\pi\) bonds are there in each molecule?

Short Answer

Expert verified
The Lewis structures for ethane (C₂H₆), ethylene (C₂H₄), and acetylene (C₂H₂) are: Ethane: H-C-C-H with 4 H atoms surrounding each C atom. Ethylene: H-C=C-H with 2 H atoms surrounding each C atom. Acetylene: H-C≡C-H with 1 H atom surrounding each C atom. Their hybridizations are sp³, sp², and sp, respectively. Ethylene and acetylene are planar, while ethane is not. Ethane has 7 sigma and 0 pi bonds, ethylene has 5 sigma and 1 pi bond, and acetylene has 3 sigma and 2 pi bonds.

Step by step solution

01

(a) Drawing Lewis Structures

To draw the Lewis structures for each hydrocarbon, we need to connect the atoms using their electrons to form molecules with complete octets. These structures represent the electron sharing between the atoms in the molecule. Ethane, C₂H₆: H - C - C - H | | H H | | H H Ethylene, C₂H₄: H - C = C - H | | H H Acetylene, C₂H₂: -C ≡ C- | | H H
02

(b) Hybridization of Carbon atoms

The hybridization of the carbon atoms can be determined by the number of surrounding atoms and lone pairs. Ethane: Each carbon atom is surrounded by 4 atoms, so it has sp³ hybridization. Ethylene: Each carbon atom is surrounded by 3 atoms, so it has sp² hybridization. Acetylene: Each carbon atom is surrounded by 2 atoms, so it has sp hybridization.
03

(c) Predicting Planar Molecules

A molecule is considered to be planar if all its atoms lie within the same plane. Ethane: The carbon atoms in ethane are sp³ hybridized and have a tetrahedral structure, so it is not planar. Ethylene: The carbon atoms in ethylene are sp² hybridized and have a trigonal planar structure, so it is planar. Acetylene: The carbon atoms in acetylene are sp hybridized and have a linear structure, so it is planar.
04

(d) Counting Sigma and Pi bonds

In each molecule, we need to count the number of sigma (single) and pi (double and triple) bonds. Ethane: Each carbon atom forms 3 sigma bonds with hydrogen atoms and 1 sigma bond with the other carbon atom. In total, there are 7 sigma bonds. Ethylene: Each carbon atom forms 2 sigma bonds with hydrogen atoms and 1 sigma bond with the other carbon atom. The double bond between the carbon atoms consists of 1 sigma bond and 1 pi bond. In total, there are 5 sigma bonds and 1 pi bond. Acetylene: Each carbon atom forms 1 sigma bond with a hydrogen atom. The triple bond between the carbon atoms consists of 1 sigma bond and 2 pi bonds. In total, there are 3 sigma bonds and 2 pi bonds.

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Most popular questions from this chapter

Name the proper three-dimensional molecular shapes for each of the following molecules or ions, showing lone pairs as needed: \((\mathbf{a}) \mathrm{ClO}_{2}^{-}(\mathbf{b}) \mathrm{SO}_{4}^{2-}(\mathbf{c}) \mathrm{NF}_{3}(\mathbf{d}) \mathrm{CCl}_{2} \mathrm{Br}_{2}(\mathbf{e}) \mathrm{SF}_{4}^{2+}\)

(a) Which geometry and central atom hybridization would you expect in the series \(\mathrm{BH}_{4}^{-}, \mathrm{CH}_{4}, \mathrm{NH}_{4}^{+} ?\) (b) What would you expect for the magnitude and direction of the bond dipoles in this series? (c) Write the formulas for the analogous species of the elements of period 3; would you expect them to have the same hybridization at the central atom?

(a) If you combine two atomic orbitals on two different atoms to make a new orbital, is this a hybrid orbital or a molecular orbital? (b) If you combine two atomic orbitals on one atom to make a new orbital, is this a hybrid orbital or a molecular orbital? (c) Does the Pauli exclusion principle (Section 6.7) apply to MOs? Explain.

Draw the Lewis structure for each of the following molecules or ions, and predict their electron-domain and molecular geometries: (a) \(\operatorname{AsF}_{3},(\mathbf{b}) \mathrm{CH}_{3}^{+},(\mathbf{c}) \operatorname{Br} \mathrm{F}_{3},(\mathbf{d}) \mathrm{ClO}_{3},(\mathbf{e}) \mathrm{XeF}_{2}\) \((\mathbf{f}) \mathrm{BrO}_{2}^{-}\)

(a) The PH \(_{3}\) molecule is polar. Does this offer experimental proof that the molecule cannot be planar? Explain. (b) It turns out that ozone, \(\mathrm{O}_{3},\) has a small dipole moment. How is this possible, given that all the atoms are the same?
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