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)