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IM Forces

IM Forces. Section 10.1. States of Matter. Forces Between Particles in Solids and Liquids. Ionic compounds Attractive forces between oppositely charged ions hold ionic compounds together. Ionic bonds are the strongest interparticle force.

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IM Forces

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  1. IM Forces Section 10.1

  2. States of Matter

  3. Forces Between Particles in Solids and Liquids • Ionic compounds • Attractive forces between oppositely charged ions hold ionic compounds together. • Ionic bonds are the strongest interparticle force. • Smaller the ion and the larger the charge on the ion the stronger the attractive forces among the ions

  4. Ionic Bonding

  5. Forces Between Particles in Solids and Liquids • Forces between molecular compounds • Intermolecular (IM) forces between molecules attract molecules to each other in the liquid and solid state. • IM forces are very weak as compared to ionic or covalent bonds

  6. IM Forces Three types of IM Forces • Dipole-dipole force • Hydrogen “bonding” • London dispersion forces See pages 440-442

  7. Interparticle Forces and Physical Properties • The stronger the attractive forces between particles in a liquid or solid, the • Higher the: • Melting point • Boiling point • Surface tension • Viscosity • Lower the: • Vapor pressure

  8. IM Forces • Dipole-dipole forces • Attractive forces between oppositely charged dipoles. • Dipole-dipole forces are found between polar compounds. • The more polar the compound the stronger the dipole-dipole force.

  9. IM Forces • Hydrogen “bonds” • Attractive force between a d+ H bonded to an O, N, or F and a d- O, N, or F generally on another molecule. • Really a relatively strong dipole-dipole force • Hydrogen bonding is the strongest of the IM forces. • H bonding is very important in water and in many biological molecules.

  10. Hydrogen “bond” is a weak attractive force between a d + hydrogen and a d-O, N, or F in a second polar bond

  11. London Dispersion Forces • London Dispersion force • Very weak and short-lasting attractive forces between temporary dipoles • See figure 10.5 • Weakest of the IM forces

  12. London Dispersion Forces • London Dispersion forces • Found between all molecules in liquid/solid state. • Of greatest significance in nonpolar molecules as it’s the only IM force between nonpolar molecules • The larger the molecule the stronger the dipersion forces.

  13. Dispersion Forces Occur between every compound and arise from the net attractive forces amount molecules which is produced from induced charge imbalances The magnitude of the Dispersion Forces is dependent upon how easily it is to distort the electron cloud. The larger the molecule the greater it’s Dispersion Forces are.

  14. Dispersion Forces and Molecular Shape • Elongated molecules have higher dispersion forces than compact molecules • Ringed structures have higher dispersion forces than straight chain molecules. • Consider: • Hexane • Cyclohexane • 2,2 – dimethyl butane

  15. Interparticle Forces • Weakest to Strongest: Intermolecular forces – all relatively weak London dispersion forces Dipole-dipole force Hydrogen Bonding Ionic bond - BY FAR THE Strongest: - not an IM Force

  16. Properties of Liquids • Freezing and boiling point • Surface tension • Capillary action • Viscosity • Which are directly related to the strength of the IM forces present between molecules?

  17. Change of State • Normal Freezing/Melting point • temperature at which the liquid and solid state co-exist at 1 atm pressure • Normal boiling point • temperature at which the liquid and gaseous state co-exist at 1 atm pressure • Predict the relative BP of: • Methane, acetone, methanol, ethanol, NaCl

  18. Surface Tension • Surface tension • Resistance of a liquid to increase its surface area • Measure of the energy needed to break the IM forces at the surface

  19. Capillary Action • Capillary action • Spontaneous rising of a liquid in a narrow tube • Related terms: • Cohesive forces – attractive forces among like molecules • Adhesive forces – attractive forces among dislike molecules

  20. See Figure 10.7, page 444 Concave meniscus Convex meniscus Adhesion > Cohesion Cohesion > adhesion

  21. Viscosity • Viscosity – resistance of a liquid to flow • Highly viscous liquids are thick (syrupy) • Consider relative viscosity of: • Propanol - • Glycerol

  22. Solid State • Amorphous solids – random arrangement of particles • Crystalline solids – highly ordered arrangement of particles • Arrangement referred to as a lattice structure • Unit cell – smallest repeating unit in the lattice • Use x-ray crystallography to determine the structure of crystalline solids

  23. Common Unit Cells – All Cubic

  24. Closest Packing and Unit Cells • Often see a lattice structure based on the closest packing possible for the particles. • Two common closest packing arrangements (pages 451/452) • Abab close packing – creates a hexagonal prism unit cell (hcp) • Abca close packing – creates a face-centered cubic unit cell

  25. Types of Crystalline Solids • Crystalline solids are defined by what’s in the lattice points • The properties of crystalline solids depends upon the strength of the attractions between the particles • Stronger the attractive forces, the higher the mp, bp…..

  26. Crystalline Solids

  27. Crystalline Solids – Atomic Solids

  28. Metallic Solids • Metal atoms in lattice points • Variety of unit cells possible • Electron sea model • delocalized valence electrons form strong nondirectional bonds • Valence e are free to move – conduct electricty and heat • Atoms remain bonded to each other as they bend/ move – malleable and ductile

  29. Diamond – Network Solid • A diamond is a gigantic molecule, each C atom is bonded to 4 other C atoms • Each C is sp3 hybridized

  30. SiO2 – Network SolidWhy isn’t SiO2classified as a molecular solid?

  31. Graphite – Atypical Network Solid • Layers of ringed carbon structures • Each C is bonded to 3 other C • Each C is sp2 hybridized

  32. Change of State Terms • Freezing • Normal freezing point • Melting • Vaporization • Normal boiling point • Condensation • Sublimation • Deposition

  33. Phase Diagram

  34. Phase Diagram Terms • Triple Point • temperature and pressure conditions when (any) 3 states co-exist • Critical Point • Critical Temp – temp • above which a gas cannot be liquefied • Critical P – P required to create a liquid at critical T

  35. Phase Diagram of Water 11.9

  36. 11.9

  37. Phase Diagram for Sulfur

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