Which one of the following pairs has only London dispersion forces as the intermolecular force between them?
1.) H2O; HF
2.)He; He
3.) HCl; HCl
4.) Ne; HCl
please help I am so lost
nub
To determine which pair has only London dispersion forces as the intermolecular force between them, we need to consider the molecular structure and polarity of each compound.
London dispersion forces, also known as Van der Waals forces, are the weakest intermolecular forces and occur in all molecules, regardless of their polarity. They result from temporary fluctuations in electron distribution within a molecule, causing an instantaneous dipole.
1.) H2O; HF: Both H2O and HF molecules contain polar bonds, resulting in dipole-dipole forces in addition to London dispersion forces. Therefore, this pair does not have only London dispersion forces.
2.) He; He: Helium (He) is a noble gas that exists as individual atoms. Since it does not form bonds or have a permanent dipole moment, the only intermolecular force present is London dispersion forces. Thus, this pair has only London dispersion forces.
3.) HCl; HCl: HCl is a polar molecule due to the difference in electronegativity between hydrogen and chlorine. Hence, in addition to London dispersion forces, dipole-dipole forces are present. Therefore, this pair does not have only London dispersion forces.
4.) Ne; HCl: Like helium, neon (Ne) is also a noble gas with only individual atoms. Since it does not have a permanent dipole moment, only London dispersion forces exist between Ne atoms. On the other hand, HCl (as discussed earlier) has both dipole-dipole and London dispersion forces. Hence, this pair does not have only London dispersion forces.
Therefore, the pair that has only London dispersion forces as the intermolecular force between them is option 2: He; He.
London dispersion forces are present is essentially all molecules but they are only one of several intermolecular forces. Ion-dipole, dipole-dipole, hydrogen bonding, etc are others but they always occur because of some polarity between molecules. For example, both H2O and HF are polar molecules. So the secret to answering this question is to pick out the pair where there is no polarity associated with any molecule of the pair.
Which do you think that is?.