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] Crystalline Solids: The Fundamental Types [11.5] States of Matter; Liquids and Solids, Paul G. Mezey.

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

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

Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey. Solids Solids are incompressible and rigid. This behaviour arises because the molecules of the solid can only vibrate because they have almost no empty space to move into.

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

Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey. Ideal gas law We might already know from earlier studies that gases behaving 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 have attractive intermolecular forces

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

Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey. Changes in state We can often change the physical 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. Phase transitions: From solid to liquid is fusion. Change in enthalpy (or heat) of fusion is  H fus From liquid to gas is vaporization. Change in enthalpy of vaporization is  H vap From solid to gas is sublimation. Change in enthalpy of sublimation is  H sub

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

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

Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey. 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. 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 vapour joining the liquid (or solid) phase.

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

Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey. 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. Temperature and vapour pressure 12

Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey. 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 GREATER vapour pressures at the GIVEN temperature) than molecules with STRONGER intermolecular forces. Temperature and vapour pressure

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

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

Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey. The normal boiling 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 = kPa Normal Boiling Point

Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey. The normal boiling 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 = kPa Normal Boiling Point

Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey. The normal boiling 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 = kPa Normal Boiling Point

Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey. The normal boiling 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 = kPa Normal Boiling Point

Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey. The normal boiling 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 = kPa Normal Boiling Point

Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey. The normal boiling 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 = kPa Normal Boiling Point

Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey. The normal boiling 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 = kPa Normal Boiling Point

Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey. The normal boiling 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 = kPa Normal Boiling Point

Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey. The normal boiling 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 = kPa Normal Boiling Point

Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey. The normal boiling 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 = kPa Normal Boiling Point

Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey. The normal boiling 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 = kPa Normal Boiling Point

Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey. The normal boiling 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 = kPa Normal Boiling Point

Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey. The normal boiling 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 = kPa Normal Boiling Point

Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey. The freezing point of a liquid is the temperature at 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. Freezing (or melting) point

Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey. Freezing and boiling points Since the normal freezing and normal boiling points of a PURE substance are 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. 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. 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. Dipole-dipole forces We’ve already seen that some molecules have a permanent molecular dipole. Since full charges are not involved in molecular dipoles, the dipole-dipole intermolecular interactions are relatively weak as 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. 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. 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. 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. 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. 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. 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. 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. Hydrogen bonding Hydrogen bonds are really just a very special case of dipole-dipole forces. H-F, H-O, and H-N bonds are very polar (larger partial charges) Also, because the hydrogen is very small, it is possible for another molecule to approach it very 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. Hydrogen bonding With London forces, boiling points will increase with molecular size (polarizability). We EXPECT boiling points to follow the trend CH 4 < SiH 4 < GeH 4 < SnH 4 and so on across the periodic table.

Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey. Hydrogen bonding This trend is generally true, except for NH 3, H 2 O, 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. IMFs and bonding at a glance

Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey. Problem For each of the following substances, list the kinds on intermolecular forces expected: BF 3 CH 3 CHOHCH 3 HI

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

Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey. Classification of solids Ionic solids are formed by regular arrangements of cations (positive) and anions (negative). Because of the strong ionic bonds involved, the melting points are usually high, and the solids are brittle and hard. NaCl is an example.

Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey. Classification of solids Molecular solids are separate molecules held together through the mainly weaker dispersion, dipole-dipole and hydrogen bond intermolecular forces. Weaker forces mean lower melting points and softer consistency. Also, since electrons can’t easily move from one molecule to another, the solids are nonconducting of electricity. Ice and sugar are examples.

Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey. Classification of solids Covalent network solids are formed by a large array of atoms. These solids are formed from repeating units, but are almost better considered to be “one large molecule”. If the arrays are three-dimensional, the solids are rigid, and so the melting points are usually high, and the solids are hard but usually not brittle. Quartz and diamond are examples.

Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey. Classification of solids Covalent network solids can also have structures of loosely held rigid sheets or chains. Graphite can be used as a lubricant because the sheets of carbon can easily slide past each other. Asbestos forms chains.

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

Chapter 11: Liquids, Solids, and Intermolecular Forces States of Matter; Liquids and Solids, Paul G. Mezey. Classification of solids Metallic solids are large arrays of metal nuclei found in an “electron sea”. Since the forces vary widely amongst metals we see widely variable melting points and hardnesses. However, since electrons can move from one atom to another, the metallic solids are good conductors of electricity and heat. Silver and iron are examples.

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

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

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

States of Matter; Liquids and Solids, Paul G. Mezey.