Intermolecular forces Flashcards
What 6 properties do intermolecular forces change?
1) Boiling point/melting point
2) State at room temp
3) Hardness and texture
4) Solubilitiy
5) Surface tension
6) Viscosity
How do intermolecular forces affect
1) (Boiling point, melting point and surface tension?)
2) How does intermolecular forces affect state at room temperature?
3) solubility?
1) stronger IMF = higher melting point, boiling point and higher Surface tension.
–> More energy to seperate molecules, due to more attraction. Molecules are held tightly together.
2) Gas = weak IMF, liquid = medium IMF, solid = High IMF,
–> weaker attraction = moves more freely, stronger attraction = closely packed.
3) “Like dissolves like” POlar molecules dissolve in polar solvents, nonpolar molecules dissolve in nonpolar solvents.
What is intermolecular forces?
The weak force of attraction between neighbouring molecules.
IMF is ALWAYS weaker than covalent and ionic bonds (strongest IMF is weaker than the IONIC and covalent bonds).
WHat are the 3 IMFS from weakest to strongest
–> what does IMF affect? What types of compounds.
LDF (in all polar and nonpolar molecules), Dipole-dipole (Only polar molecules), Hydrogen bonding (N,O,F)
Only affect molecular compounds, NOT IONIC COMPONDS (ionic compounds do NOT CONTAIN MOLECULES)
LDF characteristics? (London dispersion forces)
–> Weakest
–> Found within all molecules and atoms
-> As molecules increase in size, Strength of LDF increases
(Most prominenet in Non-polar molecules)
What is LDF?
-> Electrons are in constant movement, and for a very short temporary time, electrons are not even distrobuited. This lopsided arrangement of electrons causes instanetanous tempoarary dipoles.
- Dipoles that are short lived, and the attraction continually forms and breals (Which is why they are weak)
One side is instanteounously pos and temporary and the other is instaneously neg and temporary
–> This CAN induce dipoles in neighbouring molecules
–> This IS attracting to dipoles on neighbouring molecules.
Why do larger molecules have greater LDF?
-More protons, more electrons = greater charge imbaence when lopsided.
Note: More LDF = higher boiling and melting point, so inherinetly larger molecules have higher boiling and melting points.
DIPOLE DIPOLE: WHat is it?
The force of attraction between polar molecules attracting neighbour polear molecules
-> Stronger than LDF
-> POLAR MOLECUKLES NOT POLAR BONDS
Ie: Pole pos on one molecule is attacrted to pole neg of another molecule.
Polar molecules have perment partial charges.
Hydrogen bonds: What is it?
An extremely strong dipole dipole force between a hydrogen attom attached to (N,O,F) and annother highly electronegative molecule (N,O,F)
–> Type of dipole dipole force but the STRONGEST
WHEN AN ATOM HAS A HYDROGEN BOND, WRITE HYDROGEN BOND, LDF, DO NOT NEED TO SAY DIPOLE DIPOLE
Why is hydrogen bonding so strong
-Large difference in electronegatvitity
- Small hydrogen atom = very concentration positive pol and highly attracted to a neg pole
Between two forces (LDF, DD, H) which one is stronger?
LDF:
Bigger = stronger IMF
More bonds = stronger IMF
Dipole-Dipole:
-Stronger dipole momment (Larger different in EN) = Stronger IMF
Hydrogen bonds:
-More electronegative -> Stronger IMF
-Bigger -> Stronger IMF
-More hydrogen bonding cites -> Stronger IMF
WATER IS USUALLY THE TOP
