Final Exam F 12/11 9 am We have the room until 12 pm.

1. Final ExamF 12/119 am We have the room until 12 pm. Review Session R 12/10 2 pm SL 110 Office hours next week: T 1:30 – 3 pm W 2-4 pm R 3-4 pm Or by appointment

3. Use valence bond theory to describe the bonding about an N atom in N2H4. The Lewis electron-dot structure shows three bonds and one lone pair around each N atom. They have a tetrahedral arrangement. A tetrahedral arrangement has sp3 hybrid orbitals.

4. 1s 1s 2s 2p sp3 • The orbital diagram of the ground-state N atom is • The sp3 hybridized N atom is • Consider one N in N2F4: the two N—F bonds are formed by the overlap of a half-filled sp3 orbital with a half-filled 2p orbital on F. The N—N bond forms from the overlap of a half-filled sp3 orbital on each. The lone pair occupies one sp3 orbital.

5. 3s 3s 3p 3p 3d 3d • Use valence bond theory to describe the bonding in the ClF2- ion. • The valence orbital diagram for the Cl- ion is • After the promotion to get two half-filled orbitals, the orbital diagram is

6. sp3d 3d • The sp3d hybridized orbital diagram is • Two Cl—F bonds are formed from the overlap of two half-filled sp3d orbitals with half-filled 2p orbitals on the F atom. These use the axial positions of the trigonal bipyramid. • Three lone pairs occupy three sp3d orbitals. These are in the equatorial position of the trigonal bipyramid.

7. One hybrid orbital is required for each bond (whether a single or a multiple bond) and for each lone pair. • Multiple bonding involves the overlap of one hybrid orbital and one (for a double bond) or two (for a triple bond) nonhybridized p orbitals.

8. To describe a multiple bond, we need to distinguish between two kinds of bonds. • A s bond (sigma) has a cylindrical shape about the bond axis. It is formed either when two s orbitals overlap or with directional orbitals (p or hybrid), when they overlap along their axis. • A p bond (pi) has an electron distribution above and below the bond axis. It is formed by the sideways overlap of two parallel p orbitals. This overlap occurs when two parallel half-filled p orbitals are available after s bonds have formed.

9. Figure 10.26: Sigma and pi bonds.

10. Figure A illustrates the s bonds in C2H4. The top of Figure B shows the p orbital on each carbon at 90° to each other, with no overlap. The bottom of Figure B shows parallel p orbitals overlapping to form a p bond.

12. In acetylene, C2H2, each C has two s bonds and two p bonds. The s bonds form using the sp hybrid orbital on C. This is shown in part A. The two p bonds form from the overlap of two sets of parallel p orbitals. This is illustrated in Figure B.

14. Restricted Rotation of -Bonded Molecules A) Cis - 1,2 dichloroethylene B) trans - 1,2 dichloroethylene

15. cis trans The description of a p bond helps to explain the cis-trans isomers of 1,2-dichloroethene. The overlap of the parallel p orbitals restricts the rotation around the C=C bond. This fixes the geometric positions of Cl: either on the same side (cis) or on different sides (trans) of the C=C bond.

16. We can see this illustrated with two compounds: cis-1,2-dichloroethene trans-1,2-dichloroethene There is no net polarity; this is a nonpolar molecule. The net polarity is down; this is a polar molecule. Boiling point 60°C. Boiling point 48°C.

17. One single bond and one triple bond requires two hybrid orbitals and two sets of two parallel p orbitals. That requires sp hybridization.

18. 1s 2s 2p • Describe the bonding about the C atom in formaldehyde, CH2O, using valence bond theory. The electron arrangement is trigonal pyramidal using sp2 hybrid orbitals. The ground-state orbital diagram for C is

19. 1s 1s 2s 2p sp2 2p • After promotion, the orbital diagram is • After hybridization, the orbital diagram is

20. The C—H s bonds are formed from the overlap of two C sp2 hybrid orbitals with the 1s orbital on the H atoms. • The C—O s bond is formed from the overlap of one sp2 hybrid orbital and one O half-filled p orbital. • The C—O p bond is formed from the sideways overlap of the C 2p orbital and an O 2p orbital.

21. That's all, folks!!