Download Notes 11-1 -- KMT Liquids-Solids

Ch 11.1-11.2 Kinetic Molecular Theory of Liquids and Solids; Intermolecular Forces
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KMT in Solids & Liquids
o Condensed States – very little empty space
o Less compressible & denser than gases
o Stronger, more important intermolecular forces
o Table of properties (p. 436):
State Volume/Shape Density
Compressibility
Motion
G
Indef/Indef
Low
High
Free
*
L
Def/Indef
High
Nearly Incompressible
Flow
S
Def/Def
Highest†
Incompressible
Vibrate about fixed position
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Intermolecular Forces
o Forces between two molecules (or atoms)
o Strength determines melting and boiling point
§ Stronger IMF means more energy needed to separate molecules
• More Energy ⇒ Higher T ⇒ Higher MP, BP
o Generally much weaker than intramolecular Forces (ionic, metallic & covalent bonds)
§ All substances that are gases at room temperature and most liquids are
atomic or molecular
o Dipole-Dipole Forces (Sometimes called “van der Waals”)
§ Electrostatic force between two polar molecules
§ Can be attractive or repulsive
§ Moderate IMF: strength depends on dipole moment
§ Always smaller than full ionic interactions
o Hydrogen Bonding
§ Very strong dipole-dipole interaction
§ Involves H bonded to N, O, or F on one
molecule attracted to N, O, or F on a second
molecule
• N, O, F small atoms w/ high
electronegativity
Crystal structure and density of ice:
H-Bonding between amino acids in
DNA:
Ch 11.1-11.2 Kinetic Molecular Theory of Liquids and Solids; Intermolecular Forces
p. 2
o Binary Hydrides
§ H-Bonding makes MP of HF, H2O, and NH3 higher than predicted based on trends:
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•
IMF generally decreases as
mass decreases
o Fewer electrons →
decreased attraction (see
London Dispersion Forces
below)
Hydrogen bonding causes larger
IMF, higher boiling point.
o London Dispersion Forces
§ Induced Dipole Forces
§ Attraction between non-polar atom or molecule and an ion, polar molecule or other non-polar
atom or molecule:
§
§
§
§
Slight asymmetry in electron charge distribution in
one atom induced dipole in neighbor
Very weak since dipole is small & temporary
Present between all atoms & molecules
• Important only in absence of other forces
Strength of attraction depends on polarizability:
• Ease of separating charges
• Depends on # of electrons and shape of species
o e.g. He<Ne<Ar, etc., so BP increases down
group
o Larger molecules: CH4<C6H14 (more
electrons)
o Linear molecule allows more interactions
o Ion-Dipole Forces
§ Attraction between an ion and a polar molecule
§ Moderately Strong–Depends on ionic charge and
size of dipole
§ Solvent-solute interactions