Intermolecular Forces, Liquids, and Solids Chapter 13 Sections 1-4.
-
Upload
evan-dalton -
Category
Documents
-
view
224 -
download
0
Transcript of Intermolecular Forces, Liquids, and Solids Chapter 13 Sections 1-4.
Intermolecular Forces, Intermolecular Forces, Liquids, and SolidsLiquids, and Solids
Chapter 13Chapter 13
Sections 1-4Sections 1-4
A Molecular Comparison of Liquids A Molecular Comparison of Liquids and Solidsand Solids
Intermolecular ForcesIntermolecular Forces
Forces between particles
1. Ion-dipole
2. Dipole-dipole
3. London dispersion forces
4. Hydrogen bonding (special case of dipole-dipole)
- Interaction between an ion (Na+) and a dipole (water).- Strongest of all intermolecular forces- Important for forming solutions
- Ions are hydrated when surrounded by water
1. Ion-Dipole Forces
- Interaction between an dipole on one molecule and a dipole on an adjacent molecule.
- Dipole-dipole forces exist between neutral polar molecules.
- Weaker than ion-dipole forces
2. Dipole-Dipole Forces
Intermolecular ForcesIntermolecular Forces
- Weakest of all intermolecular forces.- All molecules (even non-polar) affect each other.- The nucleus of one molecule (or atom) attracts the
electrons of the adjacent molecule (or atom).- Electron clouds become distorted.- In that instant a polar molecule (dipole) is formed
(called an instantaneous or transient dipole).
3. London Dispersion Forces
London Dispersion Forces
- A special case of dipole-dipole forces.- Strongest of the 4 - Strongest when at least one of the molecules involved
has a covalent bond to N, O or F.
4. Hydrogen Bonding
Hydrogen Bonding
Hydrogen Bonding in Hydrogen Bonding in HH22OOHydrogen Bonding in Hydrogen Bonding in HH22OO
H-bonding is especially H-bonding is especially strong in water becausestrong in water because
• the O—H bond is very the O—H bond is very polarpolar
• there are 2 lone pairs there are 2 lone pairs on the O atomon the O atom
Accounts for many of Accounts for many of water’s unique water’s unique properties.properties.
Hydrogen Bonding• Responsible for:
– Ice Floating
• Solids are usually more closely packed than liquids and more dense
• Ice is ordered with an open structure to optimize H-bonding.
• Therefore, ice is less dense than water.
• Ice has waters arranged in an open, regular hexagon.
Intermolecular ForcesIntermolecular Forces
Hydrogen Bonding
Intermolecular ForcesIntermolecular Forces
DNA — double-helix DNA — double-helix
2 molecules each made of a chain of 2 molecules each made of a chain of nucleotides attract by H-bondsnucleotides attract by H-bonds
Specific pairing of nucleotidesSpecific pairing of nucleotides
——adenine with thymineadenine with thymine
——guanine with cytosineguanine with cytosine
Hydrogen Bonding in Biology
Intermolecular ForcesIntermolecular Forces
Chapter 14Chapter 14Colligative PropertiesColligative PropertiesSection 4Section 4
Mass percent
Concentration UnitsConcentration Units
100solution of mass total
solutionin component of masscomponent of % mass
610solution of mass total
solutionin component of masscomponent of ppm
Parts per million = ppm
solution of moles totalsolutionin component of moles
component offraction Mole
solution of literssolute moles
Molarity
solvent of kgsolute moles
Molality, m
Depend on the number of solute particles
(not on what substance is the solute)
1. Vapor Pressure Lowering
2. Boiling Point Elevation
3. Freezing Point Depression
4. Osmosis and Osmotic Pressure
Colligative PropertiesColligative Properties
Vapor Pressure Lowering
Boiling-Point Elevation & Freezing Point Depression
Boiling-Point Elevation
• Molal boiling-point-elevation constant of solvent = Kb• Molality of solute = m
mKT bb
Freezing Point Depression
Molal freezing-point-depression constant of the solvent = KfMolality = m
van’t Hoff factor = i
i = 1 for non-electrolytes
i = moles of particles per mole of dissolved electrolyte
Examples: NaCl ---> Na+ and Cl- , so i=2
Ca(NO3)2 --> Ca2+ and two NO3- , so i=3
miKT ff
Osmosis• Semipermeable membrane: permits passage of some
components of a solution. Examples: cell membranes and cellophane.
• Osmosis: the movement of a solvent from low solute concentration to high solute concentration.
• There is movement in both directions across a semipermeable membrane.
• As solvent moves across the membrane, the fluid levels in the arms becomes uneven.
Osmosis• Eventually the pressure difference between the arms
stops osmosis. ( = osmotic pressure)
MRT
RTVn
nRTV
Equation for Osmotic Pressure
= osmotic pressureV = volume of solution (L)n = moles of solute dissolvedR = Ideal Gas constantT= temperature (K)M= molarity (your book uses c)