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.