Kinetic Molecular Theory (KMT) Solids Liquids Gases Hard to compress with high densities Definite shape and definite volume NOT easy to diffuse Hard to compress and less dense NO fixed shape but definite volume Fairly easy to diffuse Easily compressed with low densities NO fixed shape, NO fixed volume Easy to diffuse

C11-1-05 KINETIC MOLECULAR THEORY OUTCOME QUESTION(S): C11-1-05 KINETIC MOLECULAR THEORY Describe the properties of gases, liquids, solids and plasma. Include: compressibility, diffusion Use the Kinetic Molecular Theory to explain properties of solids, liquids and gases. Include: intermolecular forces, elastic collisions, kinetic energy, temperature and particle motion Understand the various phase changes in terms of KMT. Include: sublimation, deposition, evaporation, condensation Vocabulary & Concepts  Intramolecular Intermolecular Crystalline Amorphous

Kinetic Molecular Theory Theory explaining how gas particles behave. If we know how gases behave, we can make predictions about liquids and solids The major assumptions (postulates): Postulate 1: Postulate 2: Postulate 3: Postulate 4: Collisions result in no change in energy and the average kinetic energy (KE) of a sample depends only on temperature. Particles constantly move and collide with other particles or the container. Particles are very small and most of the volume of a gas is empty space. There are no forces of attraction between particles or the container. Bernoulli Maxwell Boltzmann Van der Waals

Actual Particle Volume Bernoulli Particles are very small and most of the volume of a gas is empty space. Postulate 1: Gases Easily compressed with low densities NO fixed shape, NO fixed volume Easy to diffuse 99% Empty Space Volume of Gas Actual Particle Volume This postulate isn’t surprising – we know from experience that gases are easily compressed and mostly empty space (we do walk through it…)

Particles constantly move and collide with other particles or the container. Postulate 2: Maxwell Gases Easily compressed with low densities NO fixed shape, NO fixed volume Easy to diffuse Gas particles collide with the sides of the container, and exert a force. (gas pressure) Particles are in constant, random motion and are limited only by collisions with the walls of the container

Maxwell and Boltzman: An object in motion has kinetic energy – KE is directly related to particle speed. Not all particles have the same energy level at the same temperature average Temperature is the measure of the average kinetic energy of all particles in the sample Some particles have high energy, some have low – most have an average amount… Maxwell Connect: An increase in temperature (↑KE) manifests as an increase in particle motion which increases collisions which is measured by increasing gas pressure . Boltzmann

No gain or loss of kinetic energy Boltzmann Collisions result in no change in energy and the average kinetic energy (KE) of a sample depends only on temperature. Postulate 3: All collisions between particles, and with their container, are elastic. No gain or loss of kinetic energy Collisions must be elastic – have you watched an inflated ball suddenly contract (lose energy) or expand (gain energy) when just sitting there? NO

Intramolecular forces – (ie. bonds) There are two types of attractive forces that affect particles: Intramolecular forces – (ie. bonds) (within) + Na - Cl Intramolecular H O δ- δ+ Intermolecular 2. Intermolecular forces – (attraction) (between) Usually gas particles have enough kinetic energy to whiz by each other without being affected by intermolecular forces (IMF)

There are no forces of attraction between particles or the container. Postulate 4: Van der Waals Note: Kinetic theory assumes that all gases behave ideally; but, we know this is not always the case.  Gases Easily compressed with low densities NO fixed shape, NO fixed volume Easy to diffuse There can’t be much attraction between gas molecules normally since particles expand out and diffuse easily

Kinetic Molecular Theory for Gases Easily compressed with low densities. Particles of a gas must be far apart and loosely packed 2. NO fixed shape, NO fixed volume. Particles are in free, constant, random motion involving elastic collisions Easy to diffuse. Intermolecular attraction (IMFs) is weak, affording particles no restrictions

Kinetic Molecular Theory for Liquids Hard to compress and more dense than gases. Particles closer together and more densely packed NO fixed shape, but definite volume. IMFs are strong enough to allow some particle movement but limit particle distance Fairly easy to diffuse. Intermolecular attraction (IMFs) is stronger than in gases, restricting particle flow

Kinetic Molecular Theory for Solids Hard to compress with high densities. Particles very close together and very densely packed Definite shape and definite volume. Strongest IMFs severely restrict particle movement and control distance NOT easy to diffuse Intermolecular attraction (IMFs) is the strongest, completely restricting particle flow

Solids come in two main forms: crystalline and amorphous. Crystalline – particles arranged in a geometric, three-dimensional pattern. Crystal structure and symmetry play a role in determining other physical properties

Amorphous – particles have an irregular arrangement. Amorphous has Greek roots meaning “without form” Same atoms…different physical properties Other examples of amorphous: wax, rubber, plastic

Solid structures can be held by ionic attraction or covalent intermolecular forces. Ionic (ions) Polar (dipoles) C6H12O6 (sugar) NaCl Melts at 801oC Melts at 186oC IMFs can be stronger or weaker, but attraction is typically strongest in ionic solids – as evidence in melting points

C11-1-05 KINETIC MOLECULAR THEORY CAN YOU / HAVE YOU? C11-1-05 KINETIC MOLECULAR THEORY Describe the properties of gases, liquids, solids and plasma. Include: compressibility, diffusion Use the Kinetic Molecular Theory to explain properties of solids, liquids and gases. Include: intermolecular forces, elastic collisions, kinetic energy, temperature and particle motion Understand the various phase changes in terms of KMT. Include: sublimation, deposition, evaporation, condensation Vocabulary & Concepts  Intramolecular Intermolecular Crystalline Amorphous