Intermolecular Forces, Liquids, and Solids www.njctl.org Slide 3 / - PDF document

Slide 1 / 90 New Jersey Center for Teaching and Learning Progressive Science Initiative This material is made freely available at www.njctl.org and is intended for the non-commercial use of students and teachers. These materials may not be used for any commercial purpose without the written permission of the owners. NJCTL maintains its website for the convenience of teachers who wish to make their work available to other teachers, participate in a virtual professional learning community, and/or provide access to course materials to parents, students and others. Click to go to website: www.njctl.org Slide 2 / 90 Intermolecular Forces, Liquids, and Solids www.njctl.org Slide 3 / 90 Table of Contents Click on the topic to go to that section · States of Matter · Properties of Gases · Measuring Pressure · Gas Laws · Ideal Gas Law · Gas Density · Partial Pressure · Graham's Law of Effusion · Real versus Ideal Gases

Slide 4 / 90 States of Matter Return to Table of Contents Slide 5 / 90 So far this year…. 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, and learned about how atoms from molecules rearrange in chemical reactions to form new chemical compounds. Now, we're going to use intermolecular forces to combine molecules to create the common states of matter. Slide 6 / 90 Intermolecular Forces Intermolecular forces are the piece we need to add to the puzzle to explain the world around us. Without intermolecular forces, we wouldn't have tables, lakes, wall...or even our bodies. Intermolecular forces shape our world.

Slide 7 / 90 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 8 / 90 States of Matter The 2 fundamental differences between states of matter are: the distance between particles the particles' freedom to move Slide 9 / 90 States of Matter Gas Liquid Crystalline solid cool or increase cool pressure heat or heat decrease pressure disorder, freedom, ordered arrangement, Particles are far apart, particles are in fixed free to move relative total freedom, positions, to each other, much of empty space, close together close together total disorder

Slide 10 / 90 Solid Liquid Gas Enjoy this musical interlude by They Might Be Giants! Slide 11 / 90 Characteristics of the States of Matter Gas Assumes the shape of its container SHAPE VOLUME Expands to the volume of its container COMPRESSION Is compressible Flows easily FLOW Very Rapid DIFFUSION Slide 12 / 90 Characteristics of the States of Matter Liquid Assumes the shape of the part of a SHAPE container it occupies Does not expand to the volume VOLUME of the container Is virtually incompressible COMPRESSION Flows easily FLOW DIFFUSION Within a liquid, slow

Slide 13 / 90 Characteristics of the States of Matter Solid Retains its own shape SHAPE regardless of container Does not expand to the VOLUME volume of its container Is virtually incompressible COMPRESSION Does not flow FLOW Within a solid, DIFFUSION very very slow Slide 14 / 90 Condensed Phases In the solid and liquid states particles are closer together, we refer to them as condensed phases. Gas Liquid Crystalline solid cool or increase cool pressure heat or heat decrease pressure disorder, freedom, ordered arrangement, Particles are far apart, particles are in fixed free to move relative total freedom, positions, to each other, much of empty space, close together close together total disorder Slide 15 / 90 1 Which of the below is a characteristic of a gas? A It fills only a portion of its container. B Its molecules are in relatively rigid positions. Answer C It takes on the shape of its entire container. D It is not compressible. E Diffusion is very slow within it.

Slide 15 (Answer) / 90 1 Which of the below is a characteristic of a gas? A It fills only a portion of its container. B Its molecules are in relatively rigid positions. C It takes on the shape of its entire container. Answer C D It is not compressible. E Diffusion is very slow within it. [This object is a pull tab] Slide 16 / 90 2 Which of the below is a characteristic of a liquid? A It fills only a portion of its container. B Its molecules are in relatively rigid positions. C It takes on the shape of its entire container. Answer D It is compressible. E Diffusion is very rapid within it. Slide 16 (Answer) / 90 2 Which of the below is a characteristic of a liquid? A It fills only a portion of its container. B Its molecules are in relatively rigid positions. C It takes on the shape of its entire container. Answer A D It is compressible. E Diffusion is very rapid within it. [This object is a pull tab]

Slide 17 / 90 3 Which of the below is a characteristic of a solid? A It fills all of its container. B Its molecules are in relatively rigid positions. C It takes on the shape of its entire container. Answer D It is compressible. E Diffusion is very rapid within it. Slide 17 (Answer) / 90 3 Which of the below is a characteristic of a solid? A It fills all of its container. B Its molecules are in relatively rigid positions. C It takes on the shape of its entire container. Answer D It is compressible. B E Diffusion is very rapid within it. [This object is a pull tab] Slide 18 / 90 States of Matter The state of a substance at a particular temperature and pressure depends on two opposing properties: Intermolecular Forces, which pulls them together Kinetic energy of the particles, which pulls them apart Without intermolecular forces (IMF's), all molecules would be ideal gases...there would be no liquids or solids.

Slide 19 / 90 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. Slide 20 / 90 Intermolecular Forces & Boiling Points The kinetic energy of the molecules Water molecules is proportional to the temperature: as temperature rises, so does overcome their kinetic energy. intermolecular forces at 100 C. The boiling point refers to the temperature at which the molecules' energy overcomes the intermolecular forces binding them together. The higher the boiling point of a substance, the stronger the intermolecular forces. Slide 21 / 90 Intermolecular Forces H Cl Cl H Covalent bond Intermolecular (strong) attraction ( weak) The attractions between molecules, inter molecular forces, are not nearly as strong as the intra molecular 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 22 / 90 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 (LDF's) Slide 23 / 90 Dipole-Dipole Interactions The interaction between any two like charges is A dipole is a polar molecule. repulsive (black) Molecules that have 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) Only polar molecules will have this type of Intermolecular Force. Slide 24 / 90 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. Molecular Dipole Boiling Substance Weight Moment Point (amu) u(D) (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