Intermolecular Forces Flashcards
Name the three types of intermolecular forces.
- Induced dipole-dipole (London forces)
- Permanent dipole-dipole
- Hydrogen bonding
Describe the origin of an induced dipole.
- Movement of electrons produces a changing dipole
—> an instantaneous dipole will exist but its position is constantly shifting
—> induces a dipole on a neighbouring molecule
—> induces further dipoles, which then attract one another
Describe how more electrons increases the strength of an induced dipoles.
The more electrons:
- the larger the instantaneous and induced dipoles
- the greater the interactions
- the stronger the attractive forces
Where do permanent dipole-dipoles form?
Act between permanent dipoles in different polar molecules.
Why is the boiling point of hydrogen chloride higher than flourine?
- flourine molecules are non-polar and only have London forces between molecules
- hydrogen chloride molecules are polar so have London forces and permanent dipole-dipole interactions between molecules
- extra energy is needed to break the additional permanent dipole-dipole interactions between hydrogen chloride molecules
- so the boiling point of hydrogen chloride is higher than fluorine
What is hydrogen bonding?
A permanent dipole-dipole found between an electronegative atoms with a lone pair of electrons (F, O, N) and a hydrogen atom.
Why is solid ice less dense than liquid water?
- hydrogen bonds hold water molecules apart in an open lattice structure
- the water molecules in ice are further apart than in water
- therefore, solid ice is less dense than liquid water and floats
Why does water have a relatively high meting and boiling point?
- water molecules contain hydrogen bonds as well as London forces
- so a much larger quantity of energy is required to break the hydrogen bonds
State two other anomalous properties of water.
- Relatively high surface tension
- High viscosity
