Intermolecular Forces Flashcards
What are the 3 main types of intermolecular force?
Dipole-Dipole
Hydrogen Bonding
Van der Waals forces
What are dipole-dipole forces?
Attractive forces between polar molecules.
- Whatever their starting position the polar molecules ‘flip’ to dive an arrangement in which the molecules attract.
What are the 3 elements in which Hydrogen bonding occurs? (Not including H)
N, O, F
What are the conditions for Hydrogen Bonding?
Must be the very electron elements being bonded to (N,O,F) and there must be at least one lone pair on the very electronegative atom.
What is the strength of a Hydrogen Bond compared to a Covalent Bond?
A Hydrogen bond has about 10% of the strength of a Covalent Bond.
Why is Ice less dense than water?
As Ice has hydrogen bonds so the O and H can get very close together as the H atom is very small and the proton within is very exposed, while the Hydrogen bonds have been broken in water so the molecules sit further apart.
What are Van der Waals forces?
It exists between all molecules at all times, in addition to any other intermolecular force acting.
It is when the distribution of electrons is always changing so are not always completely symmetrical which creates a temporary dipole. This temporary dipole induces a dipole in another molecule. These forces are always being created and destroyed by the electrons shifting.
How strong are Van der Waals forces compared to a covalent bond?
It has about 1% of the strength of a covalent bond.
How to experiment the effect of a charged rod on liquid jets?
1) Charge a Polythene rod by rubbing vigorously on a piece of cloth.
2) Hold rod about 1cm from a jet of water issuing from a burette and note the result
3) Repeat experimentally using Hexane & Ethanol instead of Water
What are the results of the effect of a charged rod on Liquid jets?
Water moves towards the charged rod
Nothing happens with Hexane
Ethanol bends towards the charged rod
Test and observations of the test for miscibility of liquids
Test: Put a small amount of each substance in a test tube, bunging and shaking the tube. Allow the mixture to stand to see if they separate or not.
Result: Water and Ethanol (Not separated,
bubbles, mixed)
Water and Hexane (Don’t mix)
Test and Observations of the test for the solubility of Iodine in a Solution
Test: Put a small crystal (iodine) in a test tube, add 5cm3 distilled water, stopper the tube and shake. Repeat using Hexane.
Result: Iodine and Water (Yellow solution,
didn’t dissolve much)
Iodine and Hexane (Deep magenta
solution, Iodine did dissolve)
