/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 20 In which of the following molecu... [FREE SOLUTION] | 91影视

91影视

Log out

Learning Materials

Features

Discover

Chapter 9: Problem 20

In which of the following molecules can you confidently predict the bond angles about the central atom, and for which would you be a bit uncertain? Explain in each case. (a) \(\mathrm{H}_{2} \mathrm{~S}_{\text {, }}\) (b) \(\mathrm{BCl}_{3}\), (c) \(\mathrm{CH}_{3} \mathrm{I}_{,}\)(d) \(\mathrm{CBr}_{4}\), (e) \(\mathrm{TeBr}_{4}\).

Short Answer

Expert verified
The bond angles in BCl3, CH3I, and CBr4 can be confidently predicted, as they have trigonal-planar and tetrahedral molecular geometries with bond angles of 120 degrees and 109.5 degrees, respectively. However, there is uncertainty in predicting bond angles for H2S and TeBr4 due to the presence of lone pairs which causes deviation from the ideal angles in their molecular geometries.

Step by step solution

01

Determine the steric number and molecular geometry for each molecule

(a) H2S: Steric number: 2 (bonded atoms) + 2 (lone pairs) = 4 Molecular geometry: Tetrahedral (2 bonding pairs, 2 lone pairs). (b) BCl3: Steric number: 3 (bonded atoms) + 0 (lone pairs) = 3 Molecular geometry: Trigonal-planar (3 bonding pairs, 0 lone pairs). (c) CH3I: Steric number: 4 (bonded atoms) + 0 (lone pairs) = 4 Molecular geometry: Tetrahedral (4 bonding pairs, 0 lone pairs). (d) CBr4: Steric number: 4 (bonded atoms) + 0 (lone pairs) = 4 Molecular geometry: Tetrahedral (4 bonding pairs, 0 lone pairs). (e) TeBr4: Steric number: 4 (bonded atoms) + 1 (lone pair) = 5 Molecular geometry: Trigonal-bipyramidal (4 bonding pairs, 1 lone pair).
02

Determine bond type for each molecule

(a) H2S: Polar-covalent bond (b) BCl3: Polar-covalent bond (due to electronegativity difference) (c) CH3I: Polar-covalent bond (d) CBr4: Polar-covalent bond (due to electronegativity difference) (e) TeBr4: Polar-covalent bond
03

Certainty of bond angles prediction

(a) H2S: Uncertain, as the bond angle may deviate due to the presence of lone pairs causing repulsion. (b) BCl3: Confident, the bond angle in a trigonal-planar molecule is 120 degrees. (c) CH3I: Confident, the bond angle in a tetrahedral molecule is 109.5 degrees. (d) CBr4: Confident, the bond angle in a tetrahedral molecule is 109.5 degrees. (e) TeBr4: Uncertain, as the bond angles may deviate from ideal angles due to the presence of a lone pair in the trigonal-bipyramidal arrangement. In summary, the bond angles in BCl3, CH3I, and CBr4 can be confidently predicted, while there is uncertainty in predicting bond angles for H2S and TeBr4 due to the presence of lone pairs.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Over 30 million students worldwide already upgrade their learning with 91影视!

Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Steric Number
The steric number is a key concept in understanding the molecular geometry of a molecule. It refers to the total number of bonded atoms plus the number of lone pairs around a central atom. To find the steric number:
  • Add the number of atoms directly bonded to the central atom.
  • Add the number of lone pairs on the central atom.
For example, in H2S, the steric number is 4 (2 hydrogen atoms and 2 lone pairs). This calculation helps you predict the molecule's shape. It's crucial for determining the spatial arrangement of atoms, which impacts bond angles and molecule stability.
Bond Angles
Bond angles are the angles formed between three atoms across at least two bonds. They play a significant role in the shape and properties of a molecule. Bond angles are affected by:
  • Lone pair repulsions, which can decrease bond angles.
  • The molecular geometry defined by the steric number.
For example, in a tetrahedral geometry like CH3I, bond angles are typically around 109.5 degrees. However, lone pairs, as seen in H2S, can cause deviations from these ideal angles. Knowing the bond angles helps predict how a molecule interacts with other molecules and its reactivity.
Lone Pairs
Lone pairs are pairs of valence electrons that are not shared with other atoms in a molecule. These electron pairs are confined to the atom and cause repulsion against bonding pairs. This repulsion leads to an adjustment of bond angles and the overall geometry. Some effects of lone pairs include:
  • Reducing bond angles due to their higher repulsion compared to bonded pairs.
  • Altering the shape of the molecule, making it asymmetrical.
An illustrative case is TeBr4, where the presence of a lone pair yields a trigonal-bipyramidal shape with modifications, causing uncertainties in bond angle predictions.
Trigonal Bipyramidal
Trigonal bipyramidal is one of the molecular geometries categorized under the VSEPR theory. In this shape:
  • There are five positions around the central atom.
  • Five atoms or groups distribute into two types of positions: axial and equatorial.
  • The steric number is 5.
TeBr4 is an example with four bonded atoms and one lone pair, fitting this geometry. The lone pair usually occupies an equatorial position due to lower repulsion, but causes variations in bond angles, making them hard to predict accurately.
Polar Covalent Bond
A polar covalent bond occurs when two atoms with different electronegativities share electrons unequally. This results in a dipole moment due to the partial positive and negative charges created. Polar covalent bonds are common in:
  • Molecules with significant electronegativity differences between bonded atoms.
  • Intermolecular interactions affecting boiling and melting points.
Taking BCl3 as an example, the difference in electronegativity between boron and chlorine creates polar covalent bonds. Though the molecule is often considered nonpolar due to its symmetric trigonal-planar shape, understanding the nature of these bonds helps explain the molecule's physical and chemical properties.

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

Which of the following statements about hybrid orbitals is or are true? (i) After an atom undergoes sp hybridization there is one unhybridized \(p\) orbital on the atom, (ii) Under \(s p^{2}\) hybridization, the large lobes point to the vertices of an equilateral triangle, and (iii) The angle between the large lobes of \(s p^{3}\) hybrids is \(109.5^{\circ}\).

Antibonding molecular orbitals can be used to make bonds to other atoms in a molecule. For example, metal atoms can use appropriate \(d\) orbitals to overlap with the \(\pi_{2 p}^{*}\) orbitals of the carbon monoxide molecule. This is called \(d-\pi\) backbonding. (a) Draw a coordinate axis system in which the \(y\)-axis is vertical in the plane of the paper and the \(x\)-axis horizontal. Write " \(\mathrm{M}^{"}\) at the origin to denote a metal atom. (b) Now, on the \(x\) axis to the right of \(M\), draw the Lewis structure of a CO molecule, with the carbon nearest the \(M\). The CO bond axis should be on the \(x\)-axis. (c) Draw the \(\mathrm{CO} \pi_{2 p}^{*}\) orbital, with phases (see the "Closer Look" box on phases) in the plane of the paper. Two lobes should be pointing toward M. (d) Now draw the \(d_{x y}\) orbital of \(\mathrm{M}\), with phases. Can you see how they will overlap with the \(\pi_{2}^{*}\) orbital of \(\mathrm{CO}\) ? (e) What kind of bond is being made with the orbitals between \(M\) and \(\mathrm{C}_{,} \sigma\) or \(\pi\) ? (f) Predict what will happen to the strength of the CO bond in a metal\(\mathrm{CO}\) complex compared to \(\mathrm{CO}\) alone.

(a) Draw a picture showing how two \(p\) orbitals on two different atoms can be combined to make a \(\sigma\) bond. (b) Sketch a \(\pi\) bond that is constructed from \(p\) orbitals. (c) Which is generally stronger, a \(\sigma\) bond or a \(\pi\) bond? Explain. (d) Can two \(s\) orbitals combine to form a \(\pi\) bond? Explain.

The phosphorus trihalides \(\left(\mathrm{PX}_{3}\right)\) show the following variation in the bond angle \(\mathrm{X}-\mathrm{P}-\mathrm{X}: \mathrm{PF}_{3,}, 96.3^{\circ} ; \mathrm{PCl}_{3}, 100.3^{\circ}\); \(\mathrm{PBr}_{3}, 101.0^{\circ} ; \mathrm{PI}_{3}, 102.0^{\circ}\). The trend is generally attributed to the change in the electronegativity of the halogen. (a) Assuming that all electron domains are the same size, what value of the \(\mathrm{X}-\mathrm{P}-\mathrm{X}\) angle is predicted by the VSEPR model? (b) What is the general trend in the \(\mathrm{X}-\mathrm{P}-\mathrm{X}\) angle as the halide electronegativity increases? (c) Using the VSEPR model, explain the observed trend in \(\mathrm{X}-\mathrm{P}-\mathrm{X}\) angle as the electronegativity of \(\mathrm{X}\) changes. (d) Based on your answer to part (c), predict the structure of \(\mathrm{PBrCl}_{4}\).

(a) What conditions must be met if a molecule with polar bonds is nonpolar? (b) What geometries will signify nonpolar molecules for \(\mathrm{AB}_{2}, \mathrm{AB}_{3}\), and \(\mathrm{AB}_{4}\) geometries?
See all solutions

Recommended explanations on Chemistry Textbooks

Chemical Reactions

Read Explanation

Making Measurements

Read Explanation

Ionic and Molecular Compounds

Read Explanation

Physical Chemistry

Read Explanation

Chemical Analysis

Read Explanation

Chemistry Branches

Read Explanation
View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.