Forces Between Momecules(intermolecullar Forces) Flashcards
What is van der walls force also known as?
What molecules contain them?
How is it created?
What does it create?
Induced dipole-dipole force
All molecules contain them
Is created when electrons are constantly moving around so there will be an unequal electron distribution at any given time (snapshot)
Temporary dipoles
What is the relationship between big molecules and induced dipole and dipole force?
How is the force in saturated and unsaturated fats?
Larger and heavier atoms and molecules exhibit stronger dispersion forces than smaller and lighter ones. In a larger atom or molecule, the valence electrons are, on average, farther from the nuclei than in a smaller atom or molecule. They are less tightly held and can more easily form temporary dipoles.
Saturated fats=no branches so straight chains so lines closer together so stronger VDW
Unsaturated = branched chains so weaker VDW (less surface area)
In what molecules do permanent dipole and dipole attraction occur?
How are they different to VDW?
Only between polar molecules
These are permanent so don’t move around as one atom has a bigger EN than the other atom so the intermolecular force to the other molecules is always in that place it doesn’t change
What is the Hydrogen bonding ?
How do these atoms bond to hydrogen?
A special case of permanent dipole -dipole attraction where Hydrogen is bonded to a very electronegative atom (F,O,N)
-they all have lone pairs which bond to the hydrogen
In hydrogen bonding why is a strong attraction formed between the lone pairs on F/O/N and hydrogen?
As the polar bond between F/O/N leaves the H nucleus exposed as it has only one electrons.
Which is the stronger force and which is the weakest?
Strongest = Hydrogen
Permanent dipole-dipole
Weakest= van der waals/ induced
How do you work out which intermolecular forces a molecule has?
1)VDW IS(in non -polar)
2)permanent dipole-dipole(polar)
3)H is bonded to F/O/N
Why is ice less dense than water?
Ice is less dense than water because the orientation of hydrogen bonds causes molecules to push farther apart, which lowers the density
