# How to predict which substance in each of the following pairs would have the greater intermolecular forces ? a) CO_2 or OCS; b) SeO_2 or SO_2; c) CH_3CH_2CH_2NH_2 or H_2NCH_2CH_2NH_2; d) CH_3CH_3 or H_2CO; e) CH_3OH or H2CO.

!! RISPOSTA LUNGA !!

La forza del forze intermolecolari exhibited by a certain molecule goes hand in hand with its polarità and with its ability to form legami di idrogeno.

Right from the get-go, nonpolar molecules will have più debole intermolecular forces compared with polar molecules of comparable size.

So, here's a brief analysis of each pair (the molecule with the greater IMFs will be written in green)

• CO_2 e color(green)(OCS)

You're dealing with two linear molecules, the only difference between the two being that CO_2 is non polare, Mentre OCS is polar.

In CO_2's case, the bond dipole moments are equal in magnitude and point in opposite directions, so the net dipole moment will be zero. In OCS's case, the bond dipoles are not equal in magnitude because sulfur and oxygen has different elettronegatività valori.

• color(green)(SeO_2) e SO_2

This one is a little more subtle. From an elettronegatività stanpoint, selenium and sulfur are very similar; moreover, both molecules have a piegato geometria molecolare, which implies that both are polar.

However, selenium has a bigger radius than sulfur, which implies that it also has a bigger electron cloud. That translates into greater polarizability.

The positive charge that will arise on the selenium atom will be slightly bigger than that on the sulfur atom, which implies a slightly greater net dipole moment.

• CH_3CH_2CH_2NH_2 or color(green)(H_2NCH_2CH_2NH_2)

This is where the ability to form legami di idrogeno comes into play. The difference between these two ammine will be made by the additional "-NH"_2 functional group present on etilendiammina.

Questo secondo "-NH"_2 group will provide ethylenediamine with the capability to form more legami di idrogeno with neighbouring molecules when compared with propilammina, the compound that only has one "-NH"_2 group attached.

• CH_3CH_3 or color(green)(H_2CO)

Metano o CH_3CH_3, is a nonpolar molecule because the "C-H" bonds are considered to be non polare. As a result, methane will only exhibit weak Forze di dispersione di Londra.

By comparison, the electronegative oxygen will create a permanent dipole moment on the formaldehyde molecule. This will allow the molecule to exhibit interazioni dipolo-dipolo, in addition to the London dispersion forces that every molecule exhibits.

• color(green)(CH_3OH) or H_2CO

Once again, this comes down to the ability to form hydrogen bonds. Both molecules exhibit London dispersion forces and interazioni dipolo-dipolo, but the fact that ethanol, CH_3OH, has a hydrogen atom directly attached to an oxygen atom will allow it to engage in hydrogen bonding.