Chapter 5 Flashcards
Solids
Lowest Temp, Highest IMF
Liquid
In middle
Gas
Highest temp, lowest IMF
van der Waals forces,
or informally as intermolecular
attraction is
All the attractive forces between
neutral atoms and molecules
London Dispersion Forces
Present in all condensed phases
Present for all molecules, whether
they are polar or not
Weakest IMF
Larger and heavier atoms exhibit stronger dispersion forces (polarizability of large atoms)
A larger contact area
allows for more
dispersion forces
Dipole-Dipole attraction
- Only present with polar molecules
- Stronger than London dispersion forces
-Larger dipole moment = stronger dipole-dipole attraction
Hydrogen bonding
- is the strongest type of dipole-dipole attraction
- higher boiling point
- F-H, O-H, or N-H bonds
Ion-dipole interactions
- an ionic compound is dissolved
in a polar solvent
The strength of the ion-dipole
interaction determines the solubility of an ionic compound in water
Weakest to strongest INTERMFS
Dispersion, Dipole dipole, hydrogen bonding, ion dipole
INTRAMFS
covalent, ionic
Immiscible
does not mix ( lose imfs and dont gain back)
miscible
mixes (lose imfs but gain them back)
Some ionic compounds release heat when dissolved in water, some absorb
heat, others don’t have a noticeable effect on temperature, these effects are
the enthalpy of solution
The enthalpy of solution (ΔHsoln) can be broken down into two parts:
- Separating the ions: lattice energy (ΔHlat or ΔHsolute)
- Hydrating the ions: enthalpy of hydration (ΔHhydr)
lattice energy is
always positive, it takes energy to
separate opposite charges
hydration enthalpy (ΔHhydr) is
always negative, forming
intermolecular interactions (ion-dipole) releases energy
If ΔHsolute is greater than ΔHhydr, then
ΔHsoln is positive (endothermic)
If ΔHhydr is greater than ΔHlat, then
ΔHsoln is negative (exothermic)
how do greenhouse gases absorb infrared light?
- Light travels through the electromagnetic field and interacts with charged particles
- At high enough energy (UV or visible), light can directly excite electrons and break chemical bonds
- At lower energy (IR), light can only cause bonds to vibrate (as long as they have partial charges to
interact with).
So how can a non-polar molecule like CO2 absorb IR radiation?
there must be some combination(s)
of bond vibrations (stretches and/or bends) which change its dipole
moment (polarity), like CO2
Water is a much more ‘efficient’ greenhouse gas compared to CO2,
because
it is permanently polar, which means that all its modes of vibration are IR-active
The only molecules that do not absorb IR radiation at all are
homonuclear
diatomic molecules, like N2
