Physical States of Matter

Transcription

1 Intermolecular forces Chapter 5 Physical States of Matter Section 12.3 Physical States of Matter Three phases of matter solid Definite shape and volume solid liquid liquid Definite volume, shape of container gas Shape and volume of container Certain forces keep the molecules together in solids and liquids gas 1

2 Chapter 5 Physical States of Matter Physical States of Matter Physical state determined by the relative strength of cohesive and disruptive forces Cohesive forces Intramolecular forces Ion-Ion forces (ionic compounds) Ion-Dipole Forces Solvation/ydration Intermolecular forces Disruptive forces 2

3 Section 12.3 Dipole moment and boiling point Dipole-dipole forces For compounds of similar mass, the boiling point increases with increasing dipole moment Exists between polar molecules This is a fairly weak force except when one atom is hydrogen C C C 3

4 ydrogen bonding and boiling point ydrogen bond A particularly strong type of dipole-dipole interaction It exist between an electronegative atom and a hydrogen atom bonded to another electronegative atom. Molecules capable of hydrogen bonding It is an especially strong attractive force due to the small size and mass of hydrogen and the high electronegativity of oxygen Effect of hydrogen bonding 4

5 Which of the following molecules can form hydrogen bonding? C 3 C 2, C 3 C, and C 3 C Dipole-induced dipole force Exists between a non-polar compound and a polar compound Polarization: the process of inducing a dipole. Polarizability: the ease with which the electron cloud of an atom or a molecule can be distorted. Larger the molar mass, the greater the polarizability of the molecules Symmetrical distribution of electron clouds Symmetry is lost Rank the following molecules in the order of increasing polarizability Polarizability of atoms Cl 2, Br 2, and I 2 5

6 Induced dipole-induced dipole (London dispersion forces) Exists between non-polar molecules Very weak attractive force resulting from momentary (fleeting) distortions in electron distributions London Dispersion forces Why do LDF get stronger with increasing size? London Dispersion forces F 2, Cl 2, Br 2, I 2 Which halogen should have the largest dispersion forces and why? What is the impact? Symmetrical distribution of electron cloud At a given instant of time, there is an unsymmetrical distribution of electron clouds 6

7 Section 12.3 Summary for intermolecular forces Relative ranking intermolecular forces.which is the strongest force, which is the weakest force? Chapter Impact of IMF The relative strengths of IMF help explain. Physical states of matter Boiling temperaturet Solubility (miscibility) 7

8 Evaporation and Condensation Evaporation and Vaporization Vapor Pressure Evaporation or vaporization Molecules escape the surface of a liquid Vapor pressure Condensation Molecules strike and re-enter the surface of a liquid What does equilibrium mean? vaporization condensation Vapor pressure depends on strength th of cohesive forces 8

9 Vapor Pressure Vapor Pressure Vapor Pressure ydrogen bonds versus LDF Effect of Temperature Liquid Molecular weight (μ) Polarity Vapor pressure (torr) Why does T affect vapor pressure? Temperature ( o C) Vapor pressure of water (torr) Pentane 72 Nonpolar exane 86 Nonpolar eptane 100 Nonpolar 37.2 Ethanol 46 Polar (hydrogen bonds) Propanol 60 Polar (hydrogen bonds) Butanol 74 Polar (hydrogen bonds) 7.1 Water 18 Polar (hydrogen bonds) As T increases 9

10 Boiling and Boiling Point What happens to vapor pressure as temperature rises? Boiling Point Compare propanol, butane and acetone (58-60 amu). What IMF are possible? Another comparison Boiling Point Standard d or normal boiling point propanol butane acetone propane octane C 17 -ane 10

11 Boiling Point Chapter 13 Solubility Chapter 13 Miscibility Why does water have a high boiling point? Solubility A nice sounding but technically WRNG answer: Water has high boiling point because the bonds in water require a lot of energy to break. Therefore, a high temperature is needed to break the bonds and produce the gas. Miscibility Compounds with IMF of similar strength tend to be soluble like (IMF) dissolves like (IMF) 11

12 Chapter 13 Solubility *Expressed in mol alcohol/100g solvent at 20 C. Can you explain the data shown above? 12