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Kinetic Molecular Theory of Gases

Kinetic Molecular Theory of Gases. Composed of small, hard spheres of insignificant volume No forces of attraction or repulsion between particles Particles are in continuous, rapid, random straight-line motion Collisions are perfectly elastic

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Kinetic Molecular Theory of Gases

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  1. Kinetic Molecular Theory of Gases • Composed of small, hard spheres of insignificant volume • No forces of attraction or repulsion between particles • Particles are in continuous, rapid, random straight-line motion • Collisions are perfectly elastic • Describes ideal behavior of most gases at high temps and low pressures.

  2. Liquids • More dense than gas • Virtually incompressible • Takes shape of container • Definite volume Gases Solids Greater densities Density not affected by temp. Incompressible Completely rigid shape and volume • Low density • Density affected by temp. • High compressibility • Particles spread out to fill container

  3. Liquids Gases Solids Particles are very far apart Particles are close together

  4. Inter-particle Attractions • Attractions/forces that hold one particle to another in a sample.

  5. Inter-particle Attractions • Attractions/forces that hold one particle to another in a sample. • Ionic bonding • Covalent bonding • Intermolecular Forces • These are what hold the particles close together in the condensed states.

  6. Inter-particle Attractions • Type and strength affect the physical properties of a substance • For example, the STRONGER the inter-particle attractions • the ____________ the melting point • the ____________ the boiling point • the ____________ the viscosity

  7. Intermolecular forces • Inside molecules (intramolecular) the atoms are covalently bonded to each other. • Intermolecular refers to the forces between the molecules.

  8. Intermolecular forces • Weaker than intramolecular forces • Easier to vaporize water than separate to hydrogen and oxygen atoms.

  9. Intermolecular forces • Weaker than intramolecular forces • Easier to vaporize water than separate to hydrogen and oxygen atoms. • During phase changes • the molecules stay intact. • Energy used to separate molecules from one another = overcome IMFs / inter-particle attractions.

  10. Intermolecular forces • Three main types: • Dipole dipole • Hydrogen bonding • London dispersion forces

  11. 1. Dipole - Dipole • The positive and negative ends of polar molecules interact with each other, resulting in a net force of attraction. • 1% as strong as covalent bonds • Weaker with greater distance.

  12. + + - - - + + - + - - + + - - + - + + -

  13. 2. Hydrogen Bonding • Especially strong dipole-dipole forces • Occurs between molecules that contain H attached to F, O, or N • These three because- • They have high electronegativity. • They are very small. • About 10 % as strong as an ordinary covalent bond.

  14. Water d+ d- d+

  15. The Double Helix of DNA is held together by hydrogen bonding adenine thymine white = hydrogenblue = nitrogenblack = carbonred = oxygen

  16. The polymer Nylon is also held together by hydrogen bonding

  17. 3. London Dispersion Forces • Non-polar molecules (and atoms) also exert forces on each other. Otherwise, these substances could never be liquid or solid state. • carbon dioxide • iodine

  18. 3. London Dispersion Forces • Non-polar molecules (and atoms) also exert forces on each other. Otherwise, these substances could never be liquid or solid state. • Electrons are not evenly distributed at every instant in time. • Have an “instantaneous dipole”. • Induces a dipole in the atom next to it.

  19. d- d- d+ d+ d- d+ H H H H H H H H H H H H Example

  20. London Dispersion Forces • Weak, short lived. • Last longer at low temperatures. • Eventually long enough to make liquids. • Much weaker than other forces.

  21. London Dispersion Forces • Strength based on polarizabilityof the molecule • Polarizability - a measure of the extent to which the electron cloud of an atom or molecule can be distorted by an external electric charge. • More electrons = more polarizable • More polarizable = stronger dispersion forces

  22. Example Which one has stronger dispersion forces: H2 or I2? I – I H – H WHY?

  23. Summary of Intermolecular Forces • Weakest? When does it occur? • ? When does it occur? • Strongest? Conditions required for it to occur?

  24. IMFs affect . . . . • melting and boiling points  the physical state of the substance at a given temperature • conductivity • chemical reactivity • hardness or softness

  25. Summary Types of Interparticle Attractions • . • . • . • . • . • . • . Covalent bonding Ionic bonding Metallic bonding Ion-Dipole Forces Hydrogen bonding Dipole-Dipole forces Dispersion forces

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