A level chemistry how hydrogen bonding affects boiling points

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Mavs04
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Hi,
Just a question about intermolecular forces. My textbook says that only Van der Waals forces are present, but in group 6 the molecules contain polar bonds which are also distributed unevenly due to lone pairs - so wouldn’t permanent dipole - dipole forces also be present?
Or is the textbook just using “Van der Waals” to describe both?
Ty!
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emrex03
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Yh so in an exam dipole-dipole forces are accepted as well as van der Waals. Depending on the molecule, it can be polar and have dipole-dipole along with van der Waals. I think what the textbook means is that all molecules are connected with van der Waals because that is one of the properties of that force.
Hope that made some sense
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Mavs04
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(Original post by emrex03)
Yh so in an exam dipole-dipole forces are accepted as well as van der Waals. Depending on the molecule, it can be polar and have dipole-dipole along with van der Waals. I think what the textbook means is that all molecules are connected with van der Waals because that is one of the properties of that force.
Hope that made some sense
Yep thank you!
I get all of them will have VDWs forces, but in a exam when you’re explaining why the boiling point of say water is higher than the other hydrides of elements in the same group, would you talk about how the other only have dipole - dipole forces (cos boiling point is only affected by the strongest type of intermolecular force between the molecules).
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emrex03
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(Original post by Mavs04)
Yep thank you!
I get all of them will have VDWs forces, but in a exam when you’re explaining why the boiling point of say water is higher than the other hydrides of elements in the same group, would you talk about how the other only have dipole - dipole forces (cos boiling point is only affected by the strongest type of intermolecular force between the molecules).
I think you could mention either but if you don't know which has dipole-dipole, just stick with van der Waals. Usually, it gets you the mark. But for comparison, you would say water has a higher boiling point than hydrogen sulfide (for example) because it has hydrogen bonds as well as VDW, and requires more energy to overcome. Hydrogen sulfide only has VDW so needs less energy to break/weaken the bonds between molecules.
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golgiapparatus31
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They use Van der Waal's forces as an umbrella term, to mean induced dipole-dipole and permanent dipole-dipole forces
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