Within each group, assign each of the boiling points to the appropriate substance on the basis o

Within each group, assign each of the boiling points to the...

Key Concepts

Dipole-Dipole Interactions

Dipole-dipole interactions occur between molecules that have permanent dipoles, where the positive end of one molecule is attracted to the negative end of another. These forces are stronger than London dispersion forces but generally weaker than hydrogen bonds, and they significantly affect the boiling points of polar compounds.

London Dispersion Forces

London dispersion forces are the weakest type of intermolecular force and arise from temporary fluctuations in electron density that create fleeting dipoles. These forces are present in all molecules, but they are the only type of intermolecular attraction in nonpolar molecules, and their strength increases with molecular size and polarizability.

Hydrogen Bonding

Hydrogen bonding is a particularly strong type of dipole-dipole interaction that occurs when hydrogen is directly bonded to highly electronegative atoms like nitrogen, oxygen, or fluorine. These bonds greatly increase boiling points and other physical properties relative to similar molecules lacking the capacity for hydrogen bonding.

Intermolecular Forces

Intermolecular forces are the attractions between molecules that impact many physical properties, such as boiling points and melting points. The strength and type of these forces determine how much energy is required to separate molecules from one another in the liquid phase.

Boiling Point

The boiling point of a substance is a physical property that is directly related to the strength of its intermolecular forces; substances with stronger intermolecular forces require more energy (higher temperature) to transition from a liquid to a gas.

Transcript

00:01 This question is asking us to explain the differences in the boiling points of these substances based on the dominant intermolecular forces.

00:09 So for the first part say we've been given ne acon and kr if we look at these substances these are no pleases, no precursors and they are non -polar the fact that they are non -polar means the molecules are being held together by dispersion forces so this is the common factor in all of these molecules they are held together by the same type of molecules by the same type of force that is the dispassion forces because they are all non polar so what then defreciates their boiling points is the size of the molecules remember an increase in the size results in an increase in the charge which results in an increase in the magnitude of the dispersion forces.

01:08 That is, which results in an increase in the strength of.

01:16 And if the bond is stronger, it means we're going to require more energy.

01:29 So looking at these molecules, we can see that the size of the molecules decreases from ne to ar to kr.

01:38 So we would expect that neon has the smallest or the lowest boiling point while kr is the highest boiling point so hence 256 degrees celsius going on to negative 186 degrees celsius going on to the largest boiling point in this case which is 152 degree celsius so moving on to the next part here we've been given an h3 hf and h2 o now, if we look at this, in all molecules we've got an hydrogen atom that is bonded to a highly electro -negative atom.

02:36 And this type of bonding is called hydrogen bonding.

02:44 So the most dominant intermolecular force within these three compounds is the hydrogen bond.

02:50 Is the hydrogen bond so when we are looking at the differences or the strength of the hydrogen bonds the electronegativity is in the order of f should be greater than oxygen should be greater than nitrogen the electronegativities remember what brings about the hydrogen bonding is the electronegative nature of the f the o and the n so and f is f is more electronegative than o, which is also more electronegative than the nitrogen.

03:28 So from this, what would expect? would expect that fh bond should be stronger than an or h bond, which is also stronger than the nh bond.

03:43 But this is not the case.

03:48 This is not the case...

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