Chem Ch 11

• attractive forces between molecules
• these forces come into play as the temp drops on a gas
• the molecules slow until they do not have enough KE to overcome the attraction they have for each other
• the gas will then condense

• Intermolecular forces are much weaker
• Intramolecular forces hold atoms together in a molecule

the stronger the force, the higher the boiling point (and lower melting point)

attract an ion and a polar molecule to each other

• attractive forces between polar molecules
• *van der Waals force
• Dispersion will trump if it's a heavy molecule

• the separation of pos and neg charges in the atom due to proximity
• attractive forces a non polar molecule will have for a polar molecule due to proximity
• *van der Waals force

• (Instantaneous dipole-induced dipole attraction)
• an atom or non-polar molecule can, at an instance, be polar because of the movement of the electrons
• *van der Waals force
• WHAT ALLOWS NON-POLAR MOLECULES TO CONDENSE
• increases with molar mass (more e-)
• ALL MOLECULES HAVE THIS

• dipole-dipole interation between the hydrogen atom in a molecule that is directly connected with a N, O or F and a N, O or F of another molecule
• This results in a much higher b.p. and m.p. than expected

a homogeneous part of the system in contact with other parts of the system, but separated from them by a well-defined boundary (ice cubes in water)

• the ease with which the electron distribution in the atom can be distorted (induce a dipole)
• the larger the # of e-'s the greater the polarizability
• even molecules with dipoles can be polarized - causing them to be even more polar

• Ionic compounds (not really inter, INTRA)
• Hydrogen bonding
• Larger mass
• Same mass? Greater dipole moment (more polar molecule)

• the amount of energy required to stretch or increase the surface of a liquid by a unit area
• -strong intermolecular forces = high surface tension
• water is stronger than most because of H bonding

• tendency of a liquid to rise in narrow tubes or to be drawn into small openings
• brought about by cohesion and adhesion

an attraction between unlike molecules, ie. water and the sides of a glass tube

the intermolecular attraction between like molecules, ie. water molecules want to cling to each other

• a measure of a fluid's resistance to flow
• strong intermolecular forces = high viscosity
• weak " " = low viscosity

• can give off a lot of heat with only a slight decrease in temperature
• solid form is less dense than liquid
• each oxygen atom can form 2 hydrogen bonds

possesses rigid and long-range order, atoms molecules or ions occupy specific positions

• lack a well-defined arrangement and long range molecular order (no regular 3-D arrangement)
• Example - plastics, glass

basic repeating structural unit of a crystalline solid

the number of atoms (or ions) surrounding an atom (or ion) in a crystal lattice

4atoms/unit cell

2 atoms/unit cell

1 atom/unit cell

• the scattering of X-rays by the units of a crystalline solid
• occurs because the wavelength of X-rays are around the same size as distance between lattice point of crystal
• initially, the two beams are in phase
• the upper wave is scattered by top layer
• the bottom wave is scattered by the next layer

• the distance a wave must travel to be in phase again
• 2d sin @ = n h
• h = wavelength, d = distance between planes, @ = theta, n = they will give, 1st order diffraction = 1

• Contains ions
• high melting points, brittle, poor conductor of heat and electricity
• held together by electrostatic attration
• lattice points are occupied by cations (small) and anions (big)

• extensive 3-D network made entirely of covalent bonds
• high melting points, poor conductor of heat and electricity
• lattice points are occupied by atoms
• NO METALS
• examples: Diamond, graphite and quartz

• Lattice points are occupied by molecules and are held together by van der Waals forces and/or H-bonding
• melt at low temperatures (<100*C), soft, poor conductor or heat and electricity
• Non-metals or metalloids

• metals make up all the lattice points
• usually dense, melt at a wide range of temps
• good conductor of heat and electricity both in solid and liquid phase

an optically transparent fusion product of inorganic materials that has cooled to a rigid state without crystallizing (like a really cool liquid)

• the process in which a liquid is transformed into a gas
• this occurs when the molecules have enough energy to escape from the liquid surface

the pressure of the evaporated gas molecules above a liquid

the change from the gas phase to the liquid phase

• the pressure obtained when the rate of evaporation equals the rate of condensation
• increases with temperature
• decreases as intermolecular forces increase

when the rate of a forward process is exactly balanced by the rate of the reverse process

• ^H vap - the energy required to vaporize one mole of a liquid
• this is directly related to the strength of the intermolecular forces
• the stronger the intermolecular forces, the highter the ^H vap

• shows the relationship between temperature and vapor pressure
• In P = - ^H vap/RT + C
• In (P1/P2) = (^H vap/R) (1/T2 - 1/T1)
• R is 8.314 J/mol*K

• the temperature at which the vapor pressure of a liquid is equal to the external pressure
• vapor pressure and boiling point have inverse relationship (lower the pressure enough and water will boil at room temperature)
• Normal boiling point is the vapor pressure at 1 atm

phase change from liquid to solid

• phase change from solid to liquid
• ^ H fus - molar heat of fusion - the energy required to melt one mole of a solid

• it is the temperature at which the solid phase and liquid phase coexist in equilibrium
• these are the same temperature for a substance

Tc - the temperature above which the gas cannot be made to liquelfy, no matter how great the applied pressure (highest temperature at whidch a substance can exist as a liquid)

Pc - the minimum pressure that must be applied to bring about liquifaction at the critical temperature

• diagram showing phase changes from solid, to s&l equilibrium, liquid....
• temp vs time

• q = m s ^t
• t is in Celsius

• C = ms
• amount of heat required to raise the temperature of a given quantity of a substance by 1 degree Celsius

• conversion of solid directly to vapor
• ^H sub = ^H fus + ^H vap

conversion of vapor directly into solid phase

• summarizes the conditions at which a substance can exist as a solid, liquid or gas
• plot of temperature and pressure
• shows TRIPLE POINT - where all 3 phases can be in equilibrium with one another