Intermolecular Forces, Liquids, and Solids Chapter 13 Sections 1-4

A Molecular Comparison of Liquids and Solids

Intermolecular 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 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 H 2 O H-bonding is especially strong in water because the O—H bond is very polarthe O—H bond is very polar there are 2 lone pairs on the O atomthere are 2 lone pairs on the O atom Accounts for many of water’s unique 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 Forces

Hydrogen Bonding Intermolecular Forces

DNA — double-helix 2 molecules each made of a chain of nucleotides attract by H-bonds Specific pairing of nucleotides —adenine with thymine —adenine with thymine —guanine with cytosine —guanine with cytosine Hydrogen Bonding in Biology

Intermolecular Forces

Chapter 14 Colligative Properties Section 4

Mass percent Concentration Units Parts per million = ppm

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 Properties

Vapor Pressure Lowering

Boiling-Point Elevation & Freezing Point Depression

Boiling-Point Elevation Molal boiling-point-elevation constant of solvent = K b Molality of solute = m

Freezing Point Depression Molal freezing-point-depression constant of the solvent = K f Molality = 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(NO 3 ) 2 --> Ca 2+ and two NO 3 -, so i=3

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)

Equation for Osmotic Pressure  = osmotic pressure V = volume of solution (L) n = moles of solute dissolved R = Ideal Gas constant T= temperature (K) M= molarity (your book uses c)