Intermolecular forces, haloalkanes Flashcards
OZ5 OZ 6
what are intermolecular forces?
weak forces holding simple molecules together are called intermolecular forces. they are broken when heat is applied causing state changes.
what are the 3 main types of intermolecular forces?
- Instantaneous dipole induced dipole forces, IDID’s
- Permanent dipole - Permanent dipole forces, PDPD’s
- Hydrogen bonding
whats the criteria for IDID’s?
having electrons, all small molecules and the noble gases have IDID’s
how do IDID’s arise?
IDID’s arise due to the random movement of electrons in a molecule creating a temporary and instantaneous dipole dipole. this will then induce a dipole in the neighbouring molecule.
whats the criteria for a PDPD’s?
2 polar molecules, permanent dipole is attracted to another permanent dipole.
whats the criteria for hydrogen bonding?
H directly bonded to F/O/N on molecule two
whats the maximum number of hydrogen bonds that a water molecule can make?
4
whats the marking criteria for drawing a hydrogen bond diagram?
- bond angle between H and molecule 2 must be 180 degrees
- partial charges must be shown
- lone pairs must be shown on molecule 2
what is a hydrogen bond?
hydrogen bonding is just an extra strong PDPD force. it is unusually strong as F, O,and N all have a very high electronegativity which makes the H unusually partially positive. the lone pair on a F, O and N will attract this partially positive H very strongly.
what are the consequences of intermolecular forces (IMF)?
- the stronger the IMF the more energy is needed to break them so the higher the melting and boiling point
- molecules with the same type of IMF will mix with each other in the liquid state
- the strength of IMF determines the surface tension and viscosity of a liquid
- ice is less dense that water because of the IMF
what does molecules mixing when they have the same IMF show?
how some molecules will mix with water and others won’t
(oil + water)
why is ice less dense than water?
each water molecule creates 4 hydrogen bonds with neighbouring molecules, creating a giant lattice with large spaces in between. these large spaces in between mean the ice is less dense.
can you compare PDPD’s and hydrogen-bonds?
no, since as far as we know all H-bonding is of the same strength and all PDPD’s are the same strength
how can we compare IDID’s?
- size of the molecule, more e- means stronger IDID’s
- shape of molecule, more linear = molecules get closer together = stronger IDID’s
how to determine the bonds and mbp and bpt in a simple molecule?
is there a H directly bonded to F, O, N?
/ yes \ no
H-bonds polar bonds?
+ / yes \n
IDID’s symmetrical? \
| / y \ n IDID’s
high MP IDID’s PDPD’s |
+ BP | + v low
v low mp + bp IDID’s mp
| +
low mp + bp bp
