Arrange the following in order of increasing boiling point:...

Key Concepts

Ionic Bonding

Ionic bonding involves the electrostatic attraction between oppositely charged ions, resulting in very strong interactions in the solid or liquid state. Compounds with ionic bonds generally have very high boiling points or even decompose before boiling because overcoming these strong ionic interactions requires a substantial amount of energy.

Hydrogen Bonding

Hydrogen bonding is a particularly strong type of dipole-dipole interaction that occurs when hydrogen is covalently bonded to highly electronegative atoms like oxygen, nitrogen, or fluorine. Molecules capable of hydrogen bonding usually have significantly higher boiling points because these bonds require much more energy to break.

Intermolecular Forces

The boiling point of a substance is largely determined by the strength of the forces between its particles. Stronger intermolecular forces (such as hydrogen bonding, dipole-dipole interactions, or ionic attractions) require more energy to overcome, leading to higher boiling points. This concept is fundamental in understanding why substances with similar molar masses can have widely different boiling points.

London Dispersion Forces

London dispersion forces are weak, temporary attractions that occur between all molecules, regardless of their polarity. Their strength increases with molecular size and surface area. In nonpolar molecules, these forces are often the only type of intermolecular force present, resulting in comparatively low boiling points.

Molecular Polarity

Molecular polarity arises from differences in electronegativity between atoms and the molecule’s shape, which determines whether individual bond dipoles cancel out or result in a net dipole moment. Polar molecules experience dipole-dipole interactions which are stronger than London dispersion forces, typically increasing the boiling point compared to nonpolar molecules.

Transcript

00:01 When molecules have strong intermolecular forces, that means that they can go up to high temperatures without those bonds breaking.

00:12 So that means that molecules with strong intermolecular bonds will have high boiling points because they can go up to those higher temperatures without the bonds breaking.

00:28 So to solve this problem, we need to look at the different intermolecular forces that are involved.

00:33 Because remember that some kinds of intermolecular forces are stronger than other types.

00:39 First, let's look at rubidium fluoride.

00:46 So rubidium is a metal, and fluorine is a non -metal.

00:54 So that means that rubidium is going to give its electron over to fluorine, and be completely negative.

01:02 The fluorine will be completely positive.

01:04 Now they have an ionic interaction, which is the strongest kind of intermolecular force.

01:11 So that means that ribidium fluoride will have the highest melting point, or the highest boiling point as well.

01:24 The next highest will be methanol, because for methanol, we have a carbon attached to three hydrogens and an oxygen attached to another hydrogen.

01:46 Now this hydrogen right here is the reason why this molecule has the next highest boiling point.

01:52 That's because it's going to be partially positive because it's bonded to this oxygen, which is a very electronegative atom.

02:07 That means that this molecule can hydrogen bond with itself, where the partially negative oxygen can hydrogen bond with partially positive hydrogen on another molecule, and vice versa...

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