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Chapter 9: Problem 91

From their Lewis structures, determine the number of \(\sigma\) and \(\pi\) bonds in each of the following molecules or ions: (a) \(\mathrm{CO}_{2} ;\) (b) cyanogen,\((\mathrm{CN})_{2} ;(\mathbf{c})\) formaldehyde, \(\mathrm{H}_{2} \mathrm{CO}\) (d) formic acid, HCOOH, which has one H and two O atoms attached to \(\mathrm{C}\) .

Short Answer

Expert verified
(a) CO2: σ bonds = 2 π bonds = 2 (b) (CN)2: σ bonds = 3 π bonds = 4 (c) H2CO: σ bonds = 3 π bonds = 1 (d) HCOOH: σ bonds = 4 π bonds = 1

Step by step solution

01

(a) CO2 (Carbon dioxide)

: In CO2, carbon has 4 valence electrons and each oxygen atom has 6 valence electrons. 1. Draw the Lewis structure: Carbon is in the center with a double bond to each oxygen atom. 2. Identify the σ and π bonds: Each double bond contains one σ bond and one π bond. There are two double bonds in total. σ bonds = 2 π bonds = 2
02

(b) (CN)2 (Cyanogen)

: In (CN)2, each carbon has 4 valence electrons, and each nitrogen atom has 5 valence electrons. 1. Draw the Lewis structure: Each carbon atom is triple-bonded to a nitrogen atom, and the two cyanide units are connected by a single bond. 2. Identify the σ and π bonds: - In each triple bond, there is one σ bond and two π bonds. There are two triple bonds in total. - One single bond between the cyanide units is considered a σ bond. σ bonds = 1 (single bond) + 2 (triple bonds) = 3 π bonds = 4 (from the triple bonds)
03

(c) H2CO (Formaldehyde)

: In H2CO, carbon has 4 valence electrons, oxygen has 6 valence electrons, and each hydrogen atom has 1 valence electron. 1. Draw the Lewis structure: The carbon atom is in the center, double bonded to the oxygen atom and single bonded to two hydrogen atoms. 2. Identify the σ and π bonds: - In the double bond between carbon and oxygen, there is one σ bond and one π bond. - Both hydrogen atoms are bonded to the carbon atom by a single bond - two σ bonds. σ bonds = 2 (from hydrogen atoms) + 1 (from the double bond) = 3 π bonds = 1 (from the double bond)
04

(d) HCOOH (Formic acid)

: In HCOOH, carbon has 4 valence electrons, oxygen has 6 valence electrons, and hydrogen has 1 valence electron. 1. Draw the Lewis structure: The carbon atom is in the center, double bonded to one oxygen atom, single bonded to another oxygen atom, and single bonded to a hydrogen atom. The single bonded oxygen atom is also bonded to another hydrogen atom. 2. Identify the σ and π bonds: - In the double bond between carbon and oxygen, there is one σ bond and one π bond. - For the single bonds (C-O, C-H, and O-H), there are 3 σ bonds. σ bonds = 3 (from single bonds) + 1 (from the double bond) = 4 π bonds = 1 (from the double bond)

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Most popular questions from this chapter

The \(\mathrm{O}-\mathrm{H}\) bond lengths in the water molecule \(\left(\mathrm{H}_{2} \mathrm{O}\right)\) are\(0.96 \mathrm{A},\) and the \(\mathrm{H}-\mathrm{O}-\mathrm{H}\) angle is \(104.5^{\circ} .\) The dipole moment of the water molecule is 1.85 \(\mathrm{D}\) . (a) In what directions do the bond dipoles of the \(\mathrm{O}-\mathrm{H}\) bonds point? In what direction does the dipole moment vector of the water molecule point? (b) Calculate the magnitude of the bond dipole-of the \(\mathrm{O}-\mathrm{H}\) bonds. (Note: You will need to use vector addition to do this. \((\mathbf{c})\) Compare your answer from part (b) to the dipole moments of the hydrogen halides (Table 8.3\() .\) Is your answer in accord with the relative electronegativity of oxygen?

The nitrogen atoms in \(\mathrm{N}_{2}\) participate in multiple bonding, whereas those in hydrazine, \(\mathrm{N}_{2} \mathrm{H}_{4},\) do not. (a) Draw Lewis structures for both molecules. (b) What is the hybridization of the nitrogen atoms in each molecule? (c) Which molecule has the stronger \(N-N\) bond?

Dichloroethylene \(\left(\mathrm{C}_{2} \mathrm{H}_{2} \mathrm{Cl}_{2}\right)\) has three forms (isomers), each of which is a different substance. (a) Draw Lewis structures of the three isomers, all of which have a carbon-carbon double bond. ( b) Which of these isomers has a zero dipole moment? (c) How many isomeric forms can chloroethylene, \(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{Cl}\) have? Would they be expected to have dipole moments?

Consider the \(\mathrm{H}_{2}^{+}\) ion. (a) Sketch the molecular orbitals of the ion and draw its energy-level diagram. (b) How many electrons are there in the \(\mathrm{H}_{2}+\) ion? (c) Write the electron configuration of the ion in terms of its MOs. (d) What is the bond order in \(\mathrm{H}_{2}^{+} ?\) (e) Suppose that the ion is excited by light so that an electron moves from a lower-energy to a higher-energy MO. Would you expect the excited-state \(\mathrm{H}_{2}^{+}\) ion to be stable or to fall apart? (f) Which of the following statements about part (e) is correct: (i) The light excites an electron from a bonding orbital to an antibonding orbital, (ii) The light excites an electron from an antibonding orbital to a bonding orbital, or (iii) In the excited state there are more bonding electrons than antibonding electrons?

The molecule shown here is diffuoromethane \(\left(\mathrm{CH}_{2} \mathrm{F}_{2}\right),\) which is used as a refrigerant called \(\mathrm{R}-32\) . (a) Based on the structure, how many electron domains surround the C atom in this molecule? (b) Would the molecule have a nonzero dipole moment? (c) If the molecule is polar, which of the following describes the direction of the overall dipole moment vector in the molecule: (i) from the carbon atom toward a fluorine atom, (ii) from the carbon atom to a point midway between the fluorine atoms, (iii) from the carbon atom to a point midway between the hydrogen atoms, or (iv) from the carbon atom toward a hydrogen atom? [Sections 9.2 and 9.3\(]\)
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