Slide 1 / 92 Intermolecular Forces, Liquids, and Solids
Slide 2 / 92 Intermolecular Forces Intermolecular forces are the piece we need to add to the puzzle to explain the world around us. We first explained atoms, and how to build up the periodic table from quantum numbers. Then we explained how atoms combine to form molecules: the most common way we find most atoms in nature. Now, we're going to use intermolecular forces to combine molecules to create the common states of matter. Without intermolecular forces, we wouldn't have tables, lakes, wall...or even our bodies. Intermolecular forces shape our world.
Slide 3 / 92 States of Matter While there are many states of matter, the three common states that dominate our world are gases, liquids and solids. These are the states of matter we'll be studying. We won't be discussing more exotic states such as plasma, nuclear matter, etc.
Slide 4 / 92 States of Matter The fundamental differences between states of matter is: · the distance between particles · the particles' freedom to move cool or cool increase pressure heat or heat decrease pressure Gas Liquid Crystalline solid disorder, freedom, Particles are far apart, orderd arrangement, free to move relative total freedom, particles are in fixed to each other, much of empty space, positions, close together total disorder close together
Slide 5 / 92 Characteristics of the States of Matter Gas Assumes the shape of its container Expands to the volume of its container Is compressible Flows easily Diffusion within a gas is rapid Liquid Assumes the shape of the part of a container it occupies Does not expand to the volume of its container Is virtually incompressible Flows easily Diffusion within a liquid is slow Solid Retains its own shape, regardless of container Does not expand to the volume of its container Is virtually incompressible Does not flow Diffusion within a solid is very very slow
Slide 6 / 92 Condensed Phases In the solid and liquid states particles are closer together, we refer to them as condensed phases. cool or cool increase pressure heat or heat decrease pressure Gas Liquid Crystalline solid disorder, freedom, Particles are far apart, orderd arrangement, free to move relative total freedom, particles are in fixed to each other, much of empty space, positions, close together total disorder close together
Slide 7 / 92 1 Which of the following is not a type of solid? A ionic B molecular C covalent-network D supercritical E metallic
Slide 8 / 92 2 Which of the below is a characteristic of a gas? A It fills only a portion of its container. Its molecules are in relatively rigid B positions. C It takes on the shape of its container. D It is not compressible. E Diffusion is very slow within it.
Slide 9 / 92 3 Which of the below is a characteristic of a liquid? A It fills only a portion of its container. Its molecules are in relatively rigid B positions. C It takes on the shape of its container. D It is compressible. E Diffusion is very rapid within it.
Slide 10 / 92 4 Which of the below is a characteristic of a solid? A It fills all of its container. Its molecules are in relatively rigid B positions. C It takes on the shape of its container. D It is compressible. E Diffusion is very rapid within it.
Slide 11 / 92 5 Together, liquids and solids, constitute __________ phases of matter. A the compressible B the fluid C the condensed D all of the above E the disordered
Slide 12 / 92 States of Matter The state of a substance at a particular temperature and pressure depends on two opposing properties: · Intermolecular Forces: the strength of the attractions between the particles, which pulls them together · the kinetic energy of the particles, which pulls them apart Without intermolecular forces, all molecules would be ideal gases...there would be no liquids or solids.
Slide 13 / 92 Intermolecular Forces & Boiling Points Boiling represents a transition from a liquid to a gas. To make that transition, molecules in the liquid must break free of the intermolecular forces that bind them. The kinetic energy of the molecules is proportional to the temperature: as temperature rises, so does kinetic energy. The temperature where the molecules' energy overcomes intermolecular forces is called the boiling point. The boiling point is a measure of the strength of the intermolecular forces: the higher the boiling point - the stronger the intermolecular forces.
Slide 14 / 92 Intermolecular Forces Cl H Cl H Covalent bond Intermolecular (strong) attraction ( week) The attractions between molecules, intermolecular forces, are not nearly as strong as the intramolecular attractions that hold compounds together. They are, however, strong enough to control physical properties such as boiling and melting points, vapor pressures, and viscosities.
Slide 15 / 92 Intermolecular Forces There are three types of Intermolecular Forces: they are sometimes called van der Waals Forces · Dipole-dipole interactions · Hydrogen bonding · London dispersion forces
Slide 16 / 92 Dipole-Dipole Interactions The interaction between any two like charges is · Molecules that have repulsive (black) permanent dipoles are attracted to each other. + - + - · The positive end of one is - attracted to the negative end - of the other and vice-versa. + + - · These forces are only + - + important when the molecules are close to each other. The interaction between any two opposite charges is attractive ( red)
Slide 17 / 92 Dipole-Dipole Interactions The polarity of a molecule is measured by its dipole moment, m . The more polar the molecule, the greater its dipole moment. The more polar the molecule, the higher its boiling point. That's because the attraction between the dipoles holds the molecules together, not letting them boil away. Substance Molecular Dipole Boiling Weight (amu) Moment u( D) Poi nt ( K) Acetonitrile, CH 3 CN 41 3.9 355 Acetaldehyde, CH 3 CHO 44 2.7 294 Methyl chloride, CH 3 Cl 50 1.9 249 Dimethyl ether, CH 3 OCH 3 46 1.3 248 Propane, CH 3 CH 2 CH 3 44 0.1 231
Slide 18 / 92 6 Which of the below molecules will have the highest boiling point? A CH 3 CH 2 CH 3 Substance Molecular Dipole B CH 3 OCH 3 Wt. Moment C CH 3 Cl CH 3 CH 2 CH 3 44 0.1 D CH 3 CHO CH 3 OCH 3 46 1.3 E CH 3 CN CH 3 Cl 50 1.9 CH 3 CHO 44 2.7 CH 3 CN 41 3.9
Slide 19 / 92 7 Which of the below molecules will have the lowest boiling point? A CH 3 CH 2 CH 3 Substance Molecular Dipole Wt. Moment B CH 3 OCH 3 C CH 3 Cl CH 3 CH 2 CH 3 44 0.1 D CH 3 CHO CH 3 OCH 3 46 1.3 E CH 3 CN CH 3 Cl 50 1.9 CH 3 CHO 44 2.7 CH 3 CN 41 3.9
Slide 20 / 92 London Dispersion Forces London Dispersion Forces occur between all molecules. They result from the fact that electrons are in constant motion and sometimes are the same side of the molecule. When they are on one side, the molecule is polarized: one side is negative and the other is positive; the molecule acts like a dipole. That creates an electric field that oppositely polarizes nearby molecules...leading to an attraction. Let's see how that works using Helium as an example.
Slide 21 / 92 London Dispersion Forces e- While the electrons in helium repel each other, they 2+ occasionally wind up on the same side of the atom. e- Helium atom At that instant, the helium atom is polar, with an excess of electrons on one side and a shortage on the other. Another helium atom nearby, has a dipole induced in it, - δ + δ as the electrons on the left side of the first atom repel the electrons in the second. electrostatic attraction London dispersion forces, or dispersion forces, are e- e- 2+ attractions between an instantaneous dipole and an 2+ e- e- induced dipole. Helium atom 1 Helium atom 2 δ - δ + - δ + δ
Slide 22 / 92 London Dispersion Forces · These forces are present in all molecules, whether they are polar or nonpolar. · The tendency of an electron cloud to distort in this way is called polarizability. · The larger the molecule, the more polarizable it is...and the stronger the London Dispersion Force. · That means, the higher the molecular weight of a molecule, the more London Dispersion Force it experiences.
Slide 23 / 92 London Dispersion Forces · The strength of dispersion forces tends to increase with increased molecular weight. · Larger atoms and molecules have larger electron clouds which are easier to polarize. Halogen Molecular Boiling Noble Molecula Boiling Weight Point (K) gas rWeight point (K) ( amu) (amu) F 2 38.0 85.1 He 4.0 4.6 Cl 2 71.0 238.6 Ne 20.2 27.3 Br 2 159.8 332.0 Ar 39.9 87.5 I 2 253.8 457.6 Kr 83.8 120.9 Xe 131.3 166.1
Slide 24 / 92 8 Which of the molecules below will have the highest boiling point? A F 2 B Cl 2 C Br 2 D I 2
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