Chapter 10 Quiz

16. Name the hybridization scheme that corresponds to each electron geometry. (a) linear (b) trigonal planar (c) tetrahedral (d) trigonal bipyramidal (e) octahedral

(a) A linear electron geometry corresponds to sp hybridization. (b) A trigonal planar electron geometry corresponds to sp² hybridization. (c) A tetrahedral electron geometry corresponds to sp³ hybridization. (d) A trigonal bipyramidal electron geometry corresponds to sp³d hybridization. (e) An octahedral electron geometry corresponds to sp³d² hybridization.

5. Give the correct electron and molecular geometries that correspond to each set of electron groups around the central atom of a molecule. (a) four electron groups overall; three bonding groups and one lone pair. (b) four electron groups overall; two bonding groups and two lone pairs. (c) five electron groups overall; four bonding groups and one lone pair. (d) five electron groups overall; three bonding groups and two lone pairs. (e) five electron groups overall; two bonding groups and three lone pairs. (f) six electron groups overall; five bonding groups and one lone pair. (g) six electron groups overall; four bonding groups and two lone pairs.

(a) Four electron groups give a tetrahedral electron geometry, while three bonding groups and one lone pair give a trigonal pyramidal molecular geometry. (b) Four electron groups give a tetrahedral electron geometry, while two bonding groups and two lone pairs give a bent molecular geometry. (c) Five electron groups give a trigonal bipyramidal electron geometry, while four bonding groups and one pair give a seesaw molecular geometry. (d) Five electron groups give a trigonal bipyramidal electron geometry, while three bonding groups and two lone pairs give a T-shaped molecular geometry. (e) Five electron groups gives a trigonal bipyramidal electron geometry, while two bonding groups and three lone pairs give a linear geometry. (f) Six electron groups give an octahedral electron geometry, while five bonding groups and one lone pair give a square pyramidal molecular geometry. (g) Six electron groups give an octahedral electron geometry, while four bonding groups and two lone pairs give a square planar molecular geometry.

19. What is a bonding molecular orbital?

A bonding molecular orbital is lower in energy than the atomic orbitals from which it is formed. There is an increased electron density in the internuclear region.

27. Explain the difference between a paramagnetic species and a diamagnetic one.

A paramagnetic species has unpaired electrons in one or more molecular orbitals. A paramagnetic species is attracted to a magnetic field. The magnetic property is a direct result of the unpaired electron(s). The spin and angular momentum of the electrons generate tiny magnetic fields. A diamagnetic species has all of its electrons paired. The magnetic fields caused by the electron spin and orbital angular momentum tend to cancel each other. A diamagnetic species is not attracted to a magnetic field and is, in fact, slightly repelled.

2. According to VSEPR theory, what determines the geometry of a molecule?

According to VESPR theory, the repulsion between electron groups on interior atoms of a molecule determines the geometry of the molecule.

8. What is a chemical bond according to valence bond theory?

According to valence bond theory, a chemical bond results from the overlap of two half-filled orbitals with spin-pairing of the two valence electrons.

9. In valence bond theory, what determines the geometry of a molecule?

According to valence bond theory, the shape of the molecule is determined by the geometry of the overlapping orbitals.

12. How does hybridization of the atomic orbitals in the central atom of a molecule help lower the overall energy of the molecule?

Hybrid orbitals minimize the energy of the molecule by maximizing the orbital overlap in a bond.

11. What is hybridization? Why is hybridization necessary in valence bond theory?

Hybridization is a mathematical procedure in which the standard atomic orbitals are combines to form new atomic orbitals called hybrid orbitals. Hybrid orbitals are still localized on individual atoms, but they have different shapes and energies from those of standard atomic orbitals. They are necessary in valence bond theory because they correspond more closely to the actual distribution of electrons in chemically bonded atoms.

17. What is a chemical bond according to molecular orbital theory?

In molecular orbital theory, atoms will bond when the electrons in the atoms can lower their energy by occupying the molecular orbitals of the resultant molecule.

6. How do you apply VSEPR theory to predict the shape of a molecule with more than one interior atom?

Larger molecules may have two or more interior atoms. When predicting the shapes of these molecules, determine the geometry about each interior atom and use these geometries to determine the entire three-dimensional shape of the molecules.

23. How is the number of molecular orbitals approximated by a linear combination of atomic orbitals related to the number of atomic orbitals used in the approximation?

Molecular orbitals can be approximated by a linear combination of atomic orbitals (AOs). The total number of MOs formed from a particular set of AOs will always equal the number of AOs used.

29. In molecular orbital theory, what is a nonbonding orbital?

Nonbinding orbitals are atomic orbitals not involved in a bond that remain localized on the atom.

22. In molecular orbital theory, what is bond order? Why is it important?

The bond order in a diatomic molecule is the number of electrons in bonding molecular orbitals (MOs) minus the number in antibonding MOs divided by two. The higher the bond order, the stronger the bond. A negative or zero bond order indicates that a bond will not form between the ions.

7. How do you determine whether a molecule is polar? Why is polarity important?

To determine whether a molecule is polar, do the following: 1. Draw the Lewis structure for the molecule and determine the molecular geometry. 2. Determine whether the molecule contains polar bonds. 3. Determine whether the polar bonds add together to form a net dipole moment. Polarity is important because polar and nonpolar molecules have different properties. Polar molecules interact strongly with other polar molecules but don't interact with nonpolar molecules, and vice versa.

26. Why does the energy ordering of the molecular orbitals of the period 2 diatomic molecules change in going from N2 to O2?

The degree of mixing between two orbitals decreases with increasing energy difference between them. Mixing of the 2s and 2px orbitals is greater in B₂, C₂, and N₂ than in O₂, F₂, and Ne₂ because in B, C, and N, the energy levels of the atomic orbitals are more closely spaced in the O, F, and Ne. This mixing produces a change in energy ordering for the pi₂p and the sigma₂p molecular orbitals.

15. In the Lewis model, the two bonds in a double bond look identical. However, valence bond theory shows that they are not. Describe a double bond according to valence bond theory. Explain why rotation is restricted about a double bond but not about a single bond.

The double bond in Lewis theory is simply two pairs of electrons that are shared between the same two atoms. However, in valence bond theory, we see that the double bond is made up of two different kinds of bonds. The double bond in valence bond theory consists of one sigma bond and one pi bond.Valence bond theory shows that rotation about a double bond is severely restricted. Because of the side-by-side overlap of the p orbitals, the pi bond must essentially break for rotation to occur. The sigma bond consists of end-to-end overlap. Because the overlap is linear, rotation is not restricted.

4. Explain the difference between electron geometry and molecular geometry. Under what circumstances are they not the same?

The electron geometry is the geometrical arrangement of the electron groups around the central atom. The molecular geometry is the geometrical arrangement of the atoms around the central atom. The electron geometry and the molecular geometry are the same when every electron group bonds two atoms together. The presence of unbonded lone pair electrons gives a different molecular geometry and electron geometry.

20. What is an antibonding molecular orbital?

An antibonding molecular orbital is higher in energy than the atomic orbitals from which it's formed. There is less electron density in the internuclear region, which results in a node.

18. Explain the difference between hybrid atomic orbitals in valence bond theory and LCAO molecular orbitals in molecular orbital theory.

In valence bond theory, hybrid orbitals are weighted linear sums of the valence atomic orbitals of a particular atom, and the hybrid orbitals remain localized on that atom. In molecular orbital theory, the molecular orbitals are weighted linear sums of the valence atomic orbitals of all the atoms in a molecule, and many of the molecular orbitals are delocalized over the entire molecule.

10. In valence bond theory, the interaction energy between the electrons and nucleus of one atom with the electrons and nucleus of another atom is usually negative (stabilizing) when

In valence bonds theory, the interaction energy is usually negative (or stabilizing) when the interacting atomic orbitals contain a total of two electrons that can spin-pair.

21. What is the role of wave interference in determining whether a molecular orbital is bonding or antibonding?

The electrons in orbitals behave like waves. The bonding molecular orbital arises from the constructive interference between the atomic orbitals and is lower in energy than the atomic orbitals. The antibonding molecular orbital arises from the destructive interference between the atomic orbitals and is higher in energy than the atomic orbitals.

3. Name and sketch the five basic electron geometries, and state the number of electron groups corresponding to each. What constitutes an electron group?

The five basic electron geometries: 1. linear, which has two electron groups 2. trigonal planar, which has three electron groups 3. tetrahedral, which has four electron groups 4. trigonal, which has four electron groups 5. octahedral, which has six electron groups An electron group is defined as a lone pair of electrons, a single bond, a multiple bond, or even a single electron.

13. How is the number of hybrid orbitals related to the number of standard atomic orbitals that are hybridized?

The number of standard atomic orbitals added together always equals the number of hybrid orbitals formed. The total number of orbitals is conserved.

1. Why is molecular geometry important? Cite some examples.

The properties of molecules are directly related to their shape. The sensation of taste, immune response, the sense of smell, and many types of drug action all depend on shape-specific interactions between molecules and proteins.

28. When applying molecular orbital theory to heteronuclear diatomic molecules, the atomic orbitals used may be of different energies. If two atomic orbitals of different energies make two molecular orbitals, how are the energies of the molecular orbitals related to the energies of the atomic orbitals? How is the shape of the resultant molecular orbitals related to the shape of the atomic orbitals?

When two atomic orbitals are different, the weighting of each orbital in forming a molecular orbital may be different. When a molecular orbital is approximated as a linear combination of atomic orbitals of different energies, the lower-energy atomic orbital makes a greater contribution to the bonding molecular orbital and the higher-energy atomic orbital makes a greater contribution to the antibonding molecular orbital. The shape of the molecular orbital shows a greater electron density at the atom that has the lower atomic orbital energy.