Intermolecular forces - 2
- Created by: Shannon
- Created on: 08-05-14 15:40
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- Intermolecular forces
- Permanent dipoles
- Polar molecules possess permanent dipoles
- The slightly positive and slightly negative charges on the molecules cause weak electrostatic forces of attraction
- Even though these forces are weak, they are stronger than London forces
- Induced/ instantaneous dipoles (London forces)
- Found between all atoms and molecules
- Electrons in charge clouds are continuously moving
- At any one time, they are more likely to be on one side of the atom than the other
- This causes the atom to have a temporary dipole
- This dipole can cause a temporary dipole in the opposite direction of a neighbouring atom
- The two dipoles are then attracted to each other
- This dipole can cause a temporary dipole in the opposite direction of a neighbouring atom
- This causes the atom to have a temporary dipole
- At any one time, they are more likely to be on one side of the atom than the other
- London forces increase in strength as the molecule increases in size
- Electron cloud increases in size
- Hydrogen bonding
- The strongest intermolecular force
- Only happens when H covalently bonds to F.O.N
- F.O.N are very electronegative
- Pulls the bonding electrons away from the H
- Polar bond formed
- Hydrogen forms weak bonds with lone pairs of electrons on F.O.N atoms
- Because charge density is high
- Hydrogen forms weak bonds with lone pairs of electrons on F.O.N atoms
- Polar bond formed
- Pulls the bonding electrons away from the H
- Boiling and melting temperatures of alkanes with increasing chain length
- Alkanes possess covalent bonds, which are held by London forces
- The longer the carbon chain, the stronger the London forces
- More molecular surface area and more electrons to interact
- Electron cloud increases in size
- More molecular surface area and more electrons to interact
- Branched chain alkanes have smaller molecular surface areas, so the strenght of the London forces are reduced
- The longer the carbon chain, the stronger the London forces
- Alkanes possess covalent bonds, which are held by London forces
- High boiling temperatures of alcohols v alkanes
- Alcohols will form hydrogen bonds
- Hydrogen bonding increases boiling points because more energy is requires to break the interactions
- Trends in boiling temperatures of hydrogen halides
- H - F bond has the highest boiling temperature
- The charge density is high, due to concentrated charges
- Forces of attraction between neighbouring molecules is strong
- Hydrogen bonding
- Forces of attraction between neighbouring molecules is strong
- The charge density is high, due to concentrated charges
- Increases
- Due to increasing strength on London forces
- H - F bond has the highest boiling temperature
- Solubility is affected by bonding
- 2 types of solvent
- Polar e.g water
- Non-polar e.g hexane
- Ionic substances dissolve in polar solvents, e.g water
- Ions are attracted to oppositely charged ends
- Pulled away from the ionic lattice, and become surrounded by water molecules
- Hydration
- Pulled away from the ionic lattice, and become surrounded by water molecules
- Ions are attracted to oppositely charged ends
- Alcohols dissolve in polar solvents, e.g water
- The polar -OH bond in the alcohol is attrached to the polar -OH bond in the water molecule
- Hydrogen bonds form
- The polar -OH bond in the alcohol is attrached to the polar -OH bond in the water molecule
- Not all molecules with polar bonds dissolve in water
- The dipoles within halogenoalkanes are not strong enough to form hydrogen bonds
- 2 types of solvent
- Permanent dipoles
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