Ch.8 - Basic Concepts of Chemical Bonding

Problem 99a

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Chapter 8, Problem 99a

Consider the molecule C4H5N, which has the connectivity shown below. (a) After the Lewis structure for the molecule is completed, how many s and how many p bonds are there in this molecule?

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Draw the Lewis structure for the molecule C4H5N, ensuring all atoms have complete octets (or duets for hydrogen).

Identify all single bonds (σ bonds) in the molecule. Each single bond represents one σ bond.

Identify any double or triple bonds in the molecule. Each double bond consists of one σ bond and one π bond, while each triple bond consists of one σ bond and two π bonds.

Count the total number of σ bonds in the molecule by summing the single bonds and the σ components of any double or triple bonds.

Count the total number of π bonds in the molecule by summing the π components of any double or triple bonds.

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Key Concepts

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

Lewis Structures

Lewis structures are diagrams that represent the bonding between atoms in a molecule and the lone pairs of electrons that may exist. They help visualize how atoms are connected and the distribution of electrons, which is crucial for understanding molecular geometry and reactivity. In the case of C4H5N, drawing the Lewis structure allows us to identify the types of bonds present.

Types of Chemical Bonds

Chemical bonds can be classified into two main types: sigma (σ) and pi (π) bonds. Sigma bonds are formed by the head-on overlap of atomic orbitals and are the first bonds formed between two atoms, while pi bonds result from the side-to-side overlap of p orbitals and are found in double and triple bonds. Understanding these bond types is essential for determining the total number of bonds in a molecule.

Bond Counting

Counting bonds in a molecule involves identifying both the number of sigma and pi bonds present. Each single bond is a sigma bond, while double bonds consist of one sigma and one pi bond, and triple bonds contain one sigma and two pi bonds. This process is vital for answering questions about the bonding structure of C4H5N and determining the total number of s and p bonds.

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Bond Angles

Related Practice

An important reaction for the conversion of natural gas to other useful hydrocarbons is the conversion of methane to ethane. 2 CH₄(g) → C₂H₆(g) + H₂(g) In practice, this reaction is carried out in the presence of oxygen, which converts the hydrogen produced into water. 2 CH₄(g) + 12 O₂(g) → C₂H₆(g) + H₂O(g) Use Table 8.3 to estimate H for these two reactions. Why is the conversion of methane to ethane more favorable when oxygen is used? Why is the conversion of methane to ethane more favorable when oxygen is used?

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Textbook Question

Two compounds are isomers if they have the same chemical formula but different arrangements of atoms. Use Table 8.3 to estimate H for each of the following gas-phase isomerization reactions and indicate which isomer has the lower enthalpy. (d) Methyl isocyanide → Acetonitrile

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Textbook Question

The Ti²⁺ ion is isoelectronic with the Ca atom. (c) What charge would Ti have to be isoelectronic with Ca²⁺ ?

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Textbook Question

The electron affinity of oxygen is -141 kJ/mol, corresponding to the reaction O(g) + e^- → O^-(g). The lattice energy of K₂O(s) is 2238 kJ/mol. Use these data along with data in Appendix C and Figure 7.10 to calculate the 'second electron affinity' of oxygen, corresponding to the reaction O^-(g) + e^-→ O^2-(g)

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Open Question

You and a partner are asked to complete a lab entitled “Carbonates of Group 2 metal” that is scheduled to extend over two lab periods. The first lab, which is to be completed by your partner, is devoted to carrying out compositional analysis and determining the identity of the Group 2 metal (M). In the second lab, you are to determine the melting point of this compound. Upon going to the lab, you find two unlabeled vials containing white powder. You also find the following notes in your partner’s notebook—Compound 1: 40.04% M, 12.00% C, and 47.96% O (by mass); Compound 2: 69.59% M, 6.09% C, and 24.32% O (by mass). (a) What is the empirical formula for Compound 1 and the identity of M? (b) What is the empirical formula for Compound 2 and the identity of M? Upon determining the melting points of these two compounds, you find that both compounds do not melt up to the maximum temperature of your apparatus; instead, the compounds decompose and liberate a colorless gas. (c) What is the identity of the colorless gas?

Textbook Question

One scale for electronegativity is based on the concept that the electronegativity of any atom is proportional to the ionization energy of the atom minus its electron affinity: electronegativity = k1I - EA2, where k is a proportionality constant. (b) Why are both ionization energy and electron affinity relevant to the notion of electronegativity?

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