(CHE 10)Analyzing Intermolecular Forces and Their Effects on Physical Properties

What invisible forces are responsible for dictating the physical properties of matter, like boiling point?

Intermolecular forces (IMFs)

What is the weakest type of intermolecular force, which is present in all molecules?

London Dispersion Forces.

The strength of London Dispersion Forces increases with greater _____ and surface area.

molar mass

In what category of molecules do Dipole-Dipole forces occur?

They occur in all polar molecules.

What is the strongest type of intermolecular force?

Hydrogen Bonding.

Hydrogen bonding occurs when hydrogen is bonded to which three highly electronegative elements?

Nitrogen (N), Oxygen (O), or Fluorine (F).

Arrange the three main intermolecular forces from strongest to weakest.

Hydrogen Bonding > Dipole-Dipole > London Dispersion Forces.

What is the only type of intermolecular force present in carbon dioxide (CO2​)?

London dispersion forces.

When comparing two nonpolar molecules like SiF4​ and XeF4​, what factor is primarily used to determine which has stronger IMFs?

The molar mass (or number of electrons), as a larger mass leads to stronger London dispersion forces.

How do stronger intermolecular forces affect a substance's boiling point?

Stronger IMFs lead to higher boiling points.

How do stronger intermolecular forces affect a substance's vapor pressure?

Stronger IMFs lead to lower vapor pressure.

Weaker IMFs result in _____ boiling points and _____ vapor pressure.

lower; higher

Term: Vapor Pressure

The pressure exerted by the vapor of a liquid when the liquid and vapor phases are in equilibrium.

The relationship between IMF strength and vapor pressure is best described as _____.

inversely proportional (as IMF strength increases, vapor pressure decreases)

Why does Butanol (C4​H9​OH) have the highest boiling point among Methane Thiol, Butane Thiol, and Butanol?

Butanol is the only one capable of hydrogen bonding, giving it the strongest IMFs.

Why does Butane Thiol (C4​H9​SH) have a higher boiling point than Methane Thiol (H3​CSH)?

Butane Thiol has a larger molar mass, resulting in stronger London dispersion forces.

What are the strongest intermolecular forces present in dimethyl ether (CH3​OCH3​)?

Dipole-dipole forces.

What is the strongest type of intermolecular force present in ethanol (CH3​CH2​OH)?

Hydrogen bonding.

How does a molecule's surface area affect the strength of its London dispersion forces?

Greater surface area allows for more points of contact between molecules, leading to stronger London dispersion forces.

Why does methane (CH4​) have the weakest intermolecular forces of the group (CH4​, H2​NNH2​, CH3​F, H2​S)?

It is the only nonpolar molecule in the group, so it only exhibits the relatively weak London dispersion forces.

A molecule's geometry determines if its bond dipoles cancel, which in turn defines its _____.

polarity (whether it is polar or nonpolar)

For nonpolar molecules, what two properties lead to stronger London Dispersion forces?

Greater mass and larger surface area