12. Molecular Shapes & Valence Bond Theory

Bond Angles

How to Determine Bond Angle with VSEPR Table Examples, Practice Problems, Explained, Shortcut

Determine the electron geometry, molecular geometry, and
idealized bond angles for each molecule. In which cases do you
expect deviations from the idealized bond angle?
a. CF4 
b. NF3 
c. OF2 
d. H2S

Predicting Bond Angles

(a) What are the C¬C¬C bond angles in diamond?<img src="https://lightcat-files.s3.amazonaws.com/problem_images/70fd0e016d69845d-1665509158558.jpg" alt="" />

Ethyl propanoate, CH3CH2COOCH2CH3, gives a fruity 
pineapple-like smell. (e) What are the approximate bond angles around 
each carbon atom in the molecule?

Use VSEPR theory to answer the following questions:
(a) Which molecule, BF3 or PF3, has the smaller F¬X¬F
angles?

Describe the bond angles to be found in each of the following
molecular structures: (a) trigonal planar, (b) tetrahedral,
(c) octahedral, (d) linear.

Ideal Bond Angles

Determine the electron geometry, molecular geometry, and
idealized bond angles for each molecule. In which cases do you
expect deviations from the idealized bond angle?
a. PF3
b. SBr2
c. CHCl3
d. CS2

Bond Angles Concept 2

What bond angles do you expect for each of the following? 
(d) The O¬B¬O angle in BO33-

Bond Angles Example 2

In the hydrocarbon 
<img src="https://lightcat-files.s3.amazonaws.com/problem_images/879f2d498ad2b277-1661267404888.jpg" alt="" /> 
(d) Identify all the 120° bond angles in the molecule.

Lone Pairs & Bond Angles

Ideal Bond Angle is the optimal angle elements take in order to minimize repulsion.

The phosphorus trihalides 1PX32 show the following variation 
in the bond angle X¬P¬X: PF3, 96.3°; PCl3, 100.3°; 
PBr3, 101.0°; PI3, 102.0°. The trend is generally attributed 
to the change in the electronegativity of the halogen. 
(b) What is the general trend in the X¬P¬X 
angle as the halide electronegativity increases?

Give the approximate values for the indicated bond angles in 
the following molecules: 
(d) <img src="https://lightcat-files.s3.amazonaws.com/problem_images/218aed494a8094ed-1661268181421.jpg" alt="" />

75: Determining the geometry and bond angles of a molecule

Like cyclohexane (Problem 8.54), benzene also contains a sixmembered 
ring of carbon atoms, but it is flat rather than puckered. 
Explain, and predict the values of the C¬C¬C bond 
angles.
<img src="https://lightcat-files.s3.amazonaws.com/problem_images/80e6a4f57f80160b-1670474640980.jpg" alt="" />

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) H2S, (b) BCl3, (c) CH3I, (d) CBr4, (e) TeBr4.

The more lone pairs on the central element, the more compressed the bond angle, and the greater the deviation from an ideal&nbsp;bond angle.

(a) Boron trichloride 1BCl32 and the carbonate ion 1CO3 
2- 2 are both described as trigonal. What does this indicate about 
their bond angles?

Ammonia, NH3, reacts with incredibly strong bases to produce 
the amide ion, NH2-. Ammonia can also react with acids to produce the ammonium ion, NH4+. (a) Which species 
(amide ion, ammonia, or ammonium ion) has the largest H¬N¬H bond angle? (b) Which species has the smallest 
H¬N¬H bond angle?

Butadiene, C4H6, is a planar molecule that has the following 
carbon–carbon bond lengths:
<img src="https://lightcat-files.s3.amazonaws.com/problem_images/10bce61068b8e428-1676584717726.jpg" alt="" />
(a) Predict the bond angles around each of the carbon atoms 
and sketch the molecule.

Which species has the smaller bond angle, ClO4- or ClO3- ? Explain.

Give the geometry and approximate bond angles around the
central atom in CCl3-. (LO 8.1)
(a) Trigonal planar, 120°
(b) Trigonal pyramidal, 109.5°
(c) Trigonal pyramidal, 120°
(d) Bent, 109.5°

Bond Angles Concept 1

Determine the O–N–O bond angle for N­2O4, which exists as O2N–N­O­2.

Ammonia uses sp<sup3 orbits not unhybridized p atomic orbitals.

Correct, the bond angle is less than the idealized due to the effect of the lone pair.

There is a lone pair of electrons on the central N atom that affects the bond angle.

 The bond angles are determined by the geometry and the effect of the strong repulsion of lone pairs. 

What are the H&#x2212;N&#x2212;H bond angles in NH3?

The three unpaired electrons in the 3p orbitals determine the number of sigma bonds.

Correct, this configuration contains three unpaired electrons.

 A sigma bond requires overlap of an orbital with an unpaired electron. 

How many sigma bonds can a central atom with the electron configuration 3s23p3 make without hybridization?

Which species has the smaller bond angle, H3O+ or H2O? 
Explain.

Bond Angles Example 1

Give the approximate values for the indicated bond angles in 
the following molecules: 
(c)

Draw the structures of two compounds that have the composition
CH3NO2 and have all three H atoms bonded to the C. Predict
which compound has the larger ONO bond angle.

Azo dyes are organic dyes that are used for many applications,
such as the coloring of fabrics. Many azo dyes are
derivatives of the organic substance azobenzene, C12H10N2.
A closely related substance is hydrazobenzene, C12H12N2.
The Lewis structures of these two substances are
<img src="https://lightcat-files.s3.amazonaws.com/problem_images/5ecd7573c62490d7-1661269914240.jpg" alt="" />
(Recall the shorthand notation used for benzene.)
(c) Predict the N¬N¬C angles in each of the substances.

Determine the bond angle for the thiocyanate ion, SCN–.

Oxaloacetic acid is an intermediate involved in the citric 
acid cycle of food metabolism. What is the hybridization of 
the various carbon atoms in oxaloacetic acid, and what are 
the approximate values of the various bond angles?
<img src="https://lightcat-files.s3.amazonaws.com/problem_images/676cc355d68f83b7-1670481024758.jpg" alt="" />

Oceanographers study the mixing of water masses by releasing
tracer molecules at a site and then detecting their presence at
other places. The molecule trifluoromethylsulfur pentafluoride
is one such tracer. Draw an electron-dot structure for CF3SF5,
and predict the bond angles around both carbon and sulfur.

&nbsp;In the PCl­3F2 molecule the chlorine atoms exist in the equatorial positions and the fluorine atoms exist in the axial positions. Based on this information, predict the Cl–P­–Cl bond angle.

Give the approximate values for the indicated bond angles in
the following molecules:
(a)

A double bond consists of one &#963; bond and one &#960; bond.

Only single bonds consist of just a &#963; bond.

The &#960; bond in a double bond is formed by the overlap of two unhybridized p orbitals.

The orientation of the &#960; bond requires unhybridized p atomic orbitals.

The &#960; bond restricts the rotation about the carbon to carbon bond.

A double bond is stronger than a single bond.

The bond energy of double bond is larger than a single bond.

The bond length of a double bond is greater than that of a single bond.

 Review the characteristics of the orbitals that form double bonds and the spatial orientation of the components of a double bond. 

Which of the following is a false statement about double bonds?

Only the carbon atoms in this compound that are involved in carbon to carbon double bonds will exhibit sp2 hybridization.

Correct, there a seven carbon atoms involved in carbon to carbon double bonds.

sp2 carbon atoms are those involved in carbon to carbon double bonds.

DEET, or N,N-diethyl-m-toluamide, is used in many insect repellents. How many sp2 carbons are there in the following structure? <img src="https://media.pearsoncmg.com/ph/esm/esm_tro_chemistry_6/msa/content/practice-quiz/img/tro_pq_c11q12.jpg" alt="Structural formula for a complex organic molecule showing a total of 12 carbon atoms. Five of the carbon atoms are involved in only single covalent bonds while the other seven are involved in double covalent bonds." class="block">

(b) How would you expect the H¬X¬H bond angle to
vary in the series H2O, H2S, H2Se? Explain. (Hint: The size of
an electron pair domain depends in part on the electronegativity
of the central atom.)

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Clutch Prep

1. Intro to General Chemistry

2. Atoms & Elements

3. Chemical Reactions

4. BONUS: Lab Techniques and Procedures

5. BONUS: Mathematical Operations and Functions

6. Chemical Quantities & Aqueous Reactions

7. Gases

8. Thermochemistry

9. Quantum Mechanics

10. Periodic Properties of the Elements

11. Bonding & Molecular Structure

13. Liquids, Solids & Intermolecular Forces

14. Solutions

15. Chemical Kinetics

16. Chemical Equilibrium

17. Acid and Base Equilibrium

18. Aqueous Equilibrium

19. Chemical Thermodynamics

20. Electrochemistry

21. Nuclear Chemistry

22. Organic Chemistry

23. Chemistry of the Nonmetals

24. Transition Metals and Coordination Compounds

[BOOK CHEM] Clutch Version

MO Theory: Homonuclear Diatomic Molecules

Homonuclear Diatomic Molecules are composed of 2 identical elements bonded together.

Equatorial and Axial Positions

Covalent compounds with 5 or 6&nbsp;electron groups have equatorial and axial positions for surrounding elements

MO Theory: Heteronuclear Diatomic Molecules

Heteronuclear Diatomic Molecules are composed of 2 different elements bonded together.

Bond Angles&nbsp;result from surrounding elements and lone pairs around the central element positioning themselves at an optimal distance.&nbsp;

Molecular Orbital Theory

Molecular Orbital Theory&nbsp;allows us to predict the distribution of electrons within a molecule.&nbsp;

MO Theory: Bond Order

Molecular Orbital Diagrams can be used to determine the bond order of a molecule.

Electron Geometry

The simplest system for geometrical shapes that focuses on the number of electron groups around the central atom.

Hybridization

How would an&nbsp;s orbital combine with a p orbital to form a covalent bond? The answer is through hybridization where a hybrid&nbsp;oribital is formed.&nbsp;

Molecular Geometry

True Shape of Molecules that takes into account differences&nbsp;in repulsion between lone pairs and surrounding elements.