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Chapter 11: Liquids, Solids, and Intermolecular Forces

. Chapter 11: Liquids, Solids, and Intermolecular Forces. Chapter 11: Liquids, Solids, and Intermolecular Forces 11.1 Climbing Geckos and Intermolecular Forces (Suggested Reading) 11.2 Solids, Liquids and Gases: A Molecular Comparison [11.1]

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Chapter 11: Liquids, Solids, and Intermolecular Forces

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  1. . Chapter 11: Liquids, Solids, and Intermolecular Forces Chapter 11: Liquids, Solids, and Intermolecular Forces 11.1 Climbing Geckos and Intermolecular Forces (Suggested Reading) 11.2 Solids, Liquids and Gases: A Molecular Comparison [11.1] 11.3 Intermolecular Forces: The Forces that Hold Condensed Phases Together [11.4] 11.5 Vaporization and Vapor Pressure (Excluding the Clausius-Clapeyron Equation) [11.2] 11.6 Sublimation and Fusion [11.2] 11.7 Heating Curve for Water [11.2] 11.11 Crystalline Solids: The Fundamental Types [11.5] States of Matter; Liquids and Solids, Paul G. Mezey

  2. Gases . Gases are compressiblefluids. This behaviour arises because the gas molecules are in constant random motion through mostly empty space. Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  3. Liquids . Liquids are incompressiblefluids. This behaviour arises because the molecules of the liquid are in constant random motion without muchempty space to move around in. Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  4. Solids . Solids are incompressible and rigid. This behaviour arises because the molecules of the solid can only vibratebecause they havealmost noempty space to move into. Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  5. Figure . Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  6. Ideal gas law We might already know from earlier studies that gasesbehaving ideally obey the law PV = nRT where P, V, n, R, and T stand for pressure, volume, number of moles, gas constant, and absolute temperature, respectively. However, this gas law ASSUMES that molecules: 1) Have NO SIZE (no repulsive intermolecular forces) 2) DO NOT haveattractive intermolecular forces . Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  7. All molecules have intermolecular forces (IMFs) . Repulsive IMFs (real moleculeshave size) will limit the compressibility of a group of molecules. Chapter 11: Liquids, Solids, and Intermolecular Forces SQUEEZE! States of Matter; Liquids and Solids, Paul G. Mezey

  8. Changes in state . We can often changethephysical state of a substance (in a process called a phase transition) by changing the temperature and/or pressure by suitable amounts. Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  9. Phase transitions: From solid to liquid is fusion. Change in enthalpy (or heat) of fusion is DHfus From liquid to gas is vaporization. Change in enthalpy of vaporization is DHvap From solid to gas is sublimation. Change in enthalpy of sublimation is DHsub . Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  10. Phase transitions . Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  11. Enthalpy of phase transitions The enthalpy change of a phase transition tells us how much heat must be added to(or removed from) a substance in a given phase so it changes its phase. Since ALL of the the energy is involved in the phase change, the temperature REMAINS CONSTANT during the change. . Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  12. Enthalpy of phase transitions . Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  13. Vapour pressure Vapour pressure is the partial pressure (the part of the total pressure that comes from a given substance) of the vapour (gas) above the liquid (or solid) phase measured At EQUILIBRIUM at a GIVEN TEMPERATURE . Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  14. Equilibrium and vapour pressure . Vapour pressure should be measured when the vapour pressure has STOPPED CHANGING. This equilibrium means that the rate of molecules leaving the liquid (or solid) phase is BALANCED EXACTLY by the rate of the molecules in the vapourjoining the liquid (or solid) phase. Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  15. Equilibrium and vapour pressure . Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  16. Temperature and vapour pressure . The vapour pressure depends on how easily molecules can overcome attractive intermolecular forces that keep it in the liquid (or solid) phase. Higher temperatures mean molecules, on average, have more kinetic energy that COULD ALLOW the molecules to “escape” from the attractive forces. Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  17. Temperature and vapour pressure . Chapter 11: Liquids, Solids, and Intermolecular Forces 2 1 States of Matter; Liquids and Solids, Paul G. Mezey

  18. Temperature and vapour pressure . Since all groups of molecules AT THE SAME TEMPERATURE have the SAME AVERAGE KINETIC ENERGY, molecules that have WEAKER intermolecular forces are MORE VOLATILE (have GREATERvapour pressures at the GIVEN temperature) than molecules with STRONGER intermolecular forces. Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  19. Temperature and vapour pressure . In this Figure, the MOST VOLATILE (weakest IMFs) liquid is on the left, while the LEAST VOLATILE(strongest IMFs) is on the right. Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  20. Boiling Point . The boiling point of a liquid is the temperature where the vapour pressure IS THE SAME AS the external pressure. Therefore, if the external pressure changes, the boiling point temperature ALSO changes. Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  21. Normal Boiling Point . The normalboiling point of a liquid is the temperature where the vapour pressure IS THE SAME AS the “normal” external pressure: exactly 1 ATMOSPHERE. 1 atm= 760 mmHg = 101.325 kPa Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  22. Normal Boiling Point . The normalboiling point of a liquid is the temperature where the vapour pressure IS THE SAME AS the “normal” external pressure: exactly 1 ATMOSPHERE. 1 atm= 760 mmHg = 101.325 kPa Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  23. Normal Boiling Point . The normalboiling point of a liquid is the temperature where the vapour pressure IS THE SAME AS the “normal” external pressure: exactly 1 ATMOSPHERE. 1 atm= 760 mmHg = 101.325 kPa Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  24. Normal Boiling Point . The normalboiling point of a liquid is the temperature where the vapour pressure IS THE SAME AS the “normal” external pressure: exactly 1 ATMOSPHERE. 1 atm= 760 mmHg = 101.325 kPa Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  25. Normal Boiling Point . The normalboiling point of a liquid is the temperature where the vapour pressure IS THE SAME AS the “normal” external pressure: exactly 1 ATMOSPHERE. 1 atm= 760 mmHg = 101.325 kPa Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  26. Normal Boiling Point . The normalboiling point of a liquid is the temperature where the vapour pressure IS THE SAME AS the “normal” external pressure: exactly 1 ATMOSPHERE. 1 atm= 760 mmHg = 101.325 kPa Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  27. Normal Boiling Point . The normalboiling point of a liquid is the temperature where the vapour pressure IS THE SAME AS the “normal” external pressure: exactly 1 ATMOSPHERE. 1 atm= 760 mmHg = 101.325 kPa Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  28. Normal Boiling Point . The normalboiling point of a liquid is the temperature where the vapour pressure IS THE SAME AS the “normal” external pressure: exactly 1 ATMOSPHERE. 1 atm= 760 mmHg = 101.325 kPa Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  29. Normal Boiling Point . The normalboiling point of a liquid is the temperature where the vapour pressure IS THE SAME AS the “normal” external pressure: exactly 1 ATMOSPHERE. 1 atm= 760 mmHg = 101.325 kPa Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  30. Normal Boiling Point . The normalboiling point of a liquid is the temperature where the vapour pressure IS THE SAME AS the “normal” external pressure: exactly 1 ATMOSPHERE. 1 atm= 760 mmHg = 101.325 kPa Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  31. Normal Boiling Point . The normalboiling point of a liquid is the temperature where the vapour pressure IS THE SAME AS the “normal” external pressure: exactly 1 ATMOSPHERE. 1 atm= 760 mmHg = 101.325 kPa Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  32. Normal Boiling Point . The normalboiling point of a liquid is the temperature where the vapour pressure IS THE SAME AS the “normal” external pressure: exactly 1 ATMOSPHERE. 1 atm= 760 mmHg = 101.325 kPa Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  33. Normal Boiling Point . The normalboiling point of a liquid is the temperature where the vapour pressure IS THE SAME AS the “normal” external pressure: exactly 1 ATMOSPHERE. 1 atm= 760 mmHg = 101.325 kPa Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  34. Freezing (or melting) point . The freezing point of a liquid is the temperatureat which the phase transition from liquid to solid occurs. Since melting (fusion) is the exact opposite transition (solid to liquid), the freezing point and melting point are IDENTICAL. Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  35. Freezing and boiling points . Since the normal freezing and normal boiling points of a PURE substanceare fixed properties, measuring them is an easy and useful first step in identifying unknown compounds. Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  36. Intermolecular forces . The primary forces between molecules are electrostatic. They depend on charges (like charges repel, opposite charges attract), and the distance between the charges. Larger charges (like those found on ions) and smaller distances between molecules tend to lead to stronger forces. Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  37. Intermolecular forces . At ordinary conditions, the forces between molecules tend to be weakly attractive overall. These intermolecular forces are generally called van der Waals forces. These vdW forces can be subdivided into two groups. Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  38. Dipole-dipole forces . We’ve already seen that some molecules have a permanent molecular dipole. Since full charges are not involvedin molecular dipoles, the dipole-dipole intermolecular interactions are relatively weakas compared to ionic bonds, where full charges are involved. Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  39. Dipole-dipole forces . The larger the dipole moment (the molecules are more polar), the stronger the IMFs tend to be. Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  40. London (dispersion) forces . Nonpolar molecules still interact with each other despite their lack of permanent dipoles. In a nonpolar molecule, “on average,” the electrons do not prefer one part of the molecule over the other. However, at any given instant, they might not be evenly distributed and so the molecule ends up having a “temporary dipole.” Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  41. London (dispersion) forces . When a molecule with a temporary dipole comes close to another molecule, the electrons of the second molecule will try to move away from the negative partial charge of the first molecule, leading to the second molecule having a temporary induced dipole. Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  42. London (dispersion) forces . London forces tend to be very weak because the partial charges tend to be small and fleeting. However, ALL chemical species have London forces between them. Variations in the strength of London forces depend on two factors. Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  43. London (dispersion) forces . Polarizability – is the ability for electrons to move freely within the molecule. The more freely electrons can move, the larger the induced dipole can be. Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  44. London (dispersion) forces . Shape – The shape of a molecule plays a part in determining how the electrons can move in a molecule. More compact shapes are usually more symmetrical and allow less contact between molecules. They generally have smaller induced dipoles with weaker London forces. Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  45. Hydrogen bonding . A hydrogen bond is an attractive interaction between a hydrogen atom bonded to a very electronegative atom (O, N, and F), and an unshared electron pair on another electronegative atom. Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  46. Hydrogen bonding . Hydrogen bonds are really just a very special case of dipole-dipole forces. H-F, H-O, and H-N bonds are verypolar (larger partial charges) Also, because the hydrogen is very small, it is possible for another molecule to approach itvery closely (short distance). Hydrogen bonds are relatively strong intermolecular forces Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  47. Hydrogen bonding . With London forces, boiling points will increase with molecular size (polarizability). We EXPECT boiling points to follow the trend CH4 < SiH4 < GeH4 < SnH4 and so on across the periodic table. Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  48. Hydrogen bonding . This trend is generally true, except for NH3, H2O, and HF because of the hydrogen bonds (stronger than London forces) that can occur. Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  49. IMFs and bonding at a glance . Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

  50. Problem . For each of the following substances, list the kinds on intermolecular forces expected: BF3 CH3CHOHCH3 HI Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey

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