Intermolecular Forces. Flashcards
What are intermolecular forces?
These are forces between molecules.
They’re much weaker than covalent, ionic or metallic bonds.
What are the three types of intermolecular forces?
Van der Waals forces/ induced dipole-dipole (the weakest type) Permanent dipole-dipole forces Hydrogen bonding (the strongest type)
What is the van der Waals forces?
The weakest intermolecular force, caused by temporary dipoles, which causes all atoms and molecules to be attracted to each other.
What are the van der Waals forces a result of?
The electrostatic attraction between temporary dipoles and induced dipoles caused by movement of electrons in atoms and molecules.
What is the strength of Van der Waals’ forces related to?
The size of atoms and molecules.The bigger the atom or molecule the bigger the Van der Waals’ force.
In noble gases, why do the boiling points increase?
As you go down the group, the number of electrons increases.
Van der Waals forces are the only forces between noble gas atoms, so the boiling points of the gases depend on them.
As the number of electrons increases, the van der Waals forces increase, and therefore so do the boiling points.
What do the δ+ and the δ- charges on polar molecules cause?
Weak electrostatic forces of attraction between the molecules.
These are called permanent dipole dipole forces.
When can hydrogen bonding only happen?
When hydrogen is covalently bonded to fluorine, nitrogen or oxygen.
Hydrogen has a high charge density because it’s so small and fluorine, nitrogen and oxygen are very electronegative.
This bond is so polarised that the hydrogen of one molecule forms a weak bond with the fluorine, nitrogen or oxygen of another molecule.
What are hydrogen bonds?
Hydrogen bonds are permanent dipole-permanent dipole interactions.
Bonds consisting of a hydrogen atom bonded to an atom of a strongly electronegative element such as fluorine, oxygen or nitrogen are highly polar.
Hydrogen bonds are electrostatic forces of attraction between molecules which contain these highly polar bonds.
Why is ice less dense than liquid water?
In ice, molecules of H2O are held together in a simple molecular lattice by hydrogen bonds and because hydrogen bonds are relatively long ice is less dense than liquid water.
What is the weakest kind of intermolecular force?
van der Waals forces/ induced dipole interactions
Describe the bonding within and between iodine molecules.
There are covalent bonds within iodine molecules and there are van der Waals forces between iodine molecules.
The intermolecular forces mean that iodine forms a simple molecular lattice.
What are permanent dipole-dipole forces?
Weak electrostatic forces of attraction between polar molecules.
What is the strongest intermolecular force in ammonia?
Hydogen bonding
Name the strongest intermolecular force in water.
Hydogen bonding
