Chapter 6 Chemistry Test

Rank the bonds according to increasing polarity a. C-H b. N-H c. Si-H d. O-H e. Cl-H

in order of increasing polarity: c, a, b, e, d

Arrange the bonds in order of least to greatest polar character a. C-O b. Si-O c. Ge-O d. C-Cl e. C-Br

in order of least to greatest bond polarity: e d a c b

Explain the difference between non polar molecules and polar molecules

A non polar molecules has a symmetric distribution of charge while a polar molecule has a concentration of electrons on one side of a molecule

Explain the difference between a temporary dipole and a permanent dipole.

A temporary dipole forms when one molecule is close to another molecule and the electrons repel each other creating a greater electron density in one part of the molecule. Permanent dipoles are found in polar molecules in which some regions of the molecule are always partially positive and partially negative.

Decide which of the substances listed can form hydrogen bonds a. H(subscript of 2)O b. H(subscript of 2)O(subscript of 2) c. HF d. NH(subscript of 3)

All of the substances can form hydrogen bonds

Compare the location of bonding electrons in a polar covalent bond with those in a non polar covalent bond. Explain your answer

Electrons in a polar bond are closer to the more electronegative atom because of unequal sharing. Those in a non polar bond are equally shared

The refrigerant known as freon-14 is an ozone-damaging compound with the formula CF(subscript of 4). Why is the CF(subscript of 4) molecule non polar even though it contains polar bonds?

Equal distribution of charge in a symmetrical molecule

Use relative differences in electronegativity to label the ends of the polar molecules listed as partially positive or partially negative. a. HF b. HBr c. NO d. CO

H+F- H+Br- N+O- C+O-

Describe electronegativity trends in the periodic table

It increases left to right in a period and decreases top to bottom in a group

Predict which bond is the most polar a. C-O b. Si-O c. C-Cl d. C-Br

Si-O

For each pair indicate the more polar bond by circling the negative end of its dipole a. C-S,C-O b. C-F, C-N c. P-H, P-Cl

The following are circled: a. O b. F c. Cl

Determine which molecules are polar. Explain your answers. a. CH(subscript of 3)Cl b.ClF c. NCl(subscript of 3) d. BF(subscript of 3) c. CS(subscript of 2)

The polar molecules are CH(subscript of 3)Cl, ClF because each molecule is asymmetric and the charge is not distributed evenly.

Explain why hydrogen bonds are stronger than most dipole-dipole forces.

a hydrogen bond involves a large difference in electronegativity between the hydrogen atom and the atom it is attached to (O, N or F), making the bond extremely polar.

For each of the bonds listed, tell which atom is more negatively charged a. C-H b. C-N c. C-S d. C-O

a. C b. N c. S d. O

Why are dispersion forces weaker than dipole-dipole forces?

dispersion forces are between temporary dipoles (nonpolar molecules). dipole-dipole forces are between permanent dipoles (polar molecules)