Question 1

Which of the following statements best explains why water ($$\mathrm{H_2O}) is a $$polar molecule?

Accepted Answer

The molecule is bent, and the dipoles do not cancel, resulting in a partial negative charge on the oxygen atom.

Question 2

A bond between sodium ($$\mathrm{Na}$$, electronegativity $$= 0.9) $$and chlorine ($$\mathrm{Cl}$$, electronegativity $$= 3.0) is $$best classified as:

Accepted Answer

Ionic

Question 3

Which of the following molecules is nonpolar, even though it contains polar bonds?

Accepted Answer

$$\mathrm{CO_2$}$$

Question 4

What is the main type of intermolecular force present in liquid ammonia ($$\mathrm{NH_3$}$$)?

Accepted Answer

Hydrogen bonding

Question 5

Which of the following best describes the difference between dipole-dipole forces and hydrogen bonds?

Accepted Answer

Hydrogen bonds are a special, stronger type of dipole-dipole force that occur when hydrogen is bonded to F, O, or N.

Question 6

A hydrocarbon such as octane ($$\mathrm{C_8H_{18}}) is $$nonpolar because:

Accepted Answer

It contains only C–H bonds, which are nonpolar, and has a symmetrical charge distribution.

Question 7

Which of the following molecules can form hydrogen bonds with water?

Accepted Answer

$$\mathrm{C_2H_5OH} ($$ethanol)

Question 8

Given the following electronegativity values: $$\mathrm{O} = 3.5$$, $$\mathrm{H} = 2.1$$, $$\mathrm{C} = 2.5$$, which bond is the most polar?

Accepted Answer

$$\mathrm{O-H}$$

Question 9

Which of the following best explains why phospholipids form bilayers in cell membranes?

Accepted Answer

Their dual nature, with hydrophilic polar heads and hydrophobic nonpolar tails, causes them to arrange with heads facing water and tails away from water.

Question 10

Which of the following statements about dispersion forces is correct?

Accepted Answer

They are weak attractions caused by temporary dipoles in all molecules, especially nonpolar ones.

Question 11

A molecule of pentanol ($$\mathrm{C_5H_{11}OH}) $$contains both polar and nonpolar regions. Which part of the molecule is responsible for its ability to dissolve in water?

Accepted Answer

The $$-\mathrm{OH} ($$hydroxyl) group

Question 12

Which of the following compounds would you expect to have the highest melting point?

Accepted Answer

$$\mathrm{NaCl} ($$ionic bonding)

Question 13

Which of the following best describes the main intermolecular force in liquid bromine ($$\mathrm{Br_2$}$$)?

Accepted Answer

Dispersion forces

Question 14

A student is asked to predict the type of bond in $$\mathrm{Cl_2$}$$ using electronegativity values ($$\mathrm{Cl} = 3.0). $$What is the correct answer and why?

Accepted Answer

Nonpolar covalent, because the electronegativity difference is $$0$$

Question 15

Which of the following molecules is polar due to its molecular geometry, even though all the bonds are identical?

Accepted Answer

$$\mathrm{NH_3$}$$

Question 16

Which of the following best explains why $$\mathrm{CH_4$} ($$methane) is a nonpolar molecule?

Accepted Answer

It contains only nonpolar bonds and has a symmetrical tetrahedral shape.

Question 17

Which of the following is the strongest type of attractive force present in a sample of ethanol ($$\mathrm{CH_3CH_2OH}$$)?

Accepted Answer

Hydrogen bonding

Question 18

A molecule has a trigonal planar shape and contains three identical polar bonds arranged symmetrically. What is the overall polarity of the molecule?

Accepted Answer

Nonpolar, because the dipoles cancel due to symmetry

Question 19

Which of the following best describes the main attractive force between molecules in solid iodine ($$\mathrm{I_2$}$$)?

Accepted Answer

Dispersion forces

Question 20

Which of the following best explains why ionic compounds generally have higher melting points than molecular compounds?

Accepted Answer

Ionic compounds have stronger attractive forces between ions than the intermolecular forces in molecular compounds.

Molecular Polarity and Intermolecular Forces (Chapter 7) – Study Notes

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