Chapter 13 Liquids and Solids by Christopher Hamaker © 2011 Pearson Education, Inc. Chapter 13

Properties of Liquids Unlike gases, liquids do not respond dramatically to temperature and pressure changes. We can study the liquid state and make five general observations. Liquids have a variable shape, but a fixed volume. Liquids take the shape of their container. Liquids usually flow readily. However, not all liquids flow at the same rate. Liquids do not compress or expand significantly. The volume of a liquid varies very little as the temperature and pressure change. © 2011 Pearson Education, Inc. Chapter 13

Properties of Liquids, Continued 4. Liquids have a high density compared to gases. Liquids are about 1000 times more dense than gases. 5. Liquids that are soluble mix homogeneously. Liquids diffuse more slowly than gases, but eventually form a homogeneous mixture. © 2011 Pearson Education, Inc. Chapter 13

Intermolecular Bond Concept An intermolecular bond is an attraction between molecules, whereas an intramolecular bond is between atoms in a molecule. Some properties of liquids, such as vapor pressure, viscosity, and surface tension, are determined by the strength of attraction between molecules. Intermolecular bonds are much weaker than intramolecular bonds. © 2011 Pearson Education, Inc. Chapter 13

Intermolecular Bonds Recall that a polar molecule has positive and negative charges concentrated in different regions due to unequal sharing of electrons in bonds. This uneven distribution of electrons in a molecule is called a dipole. Intermolecular attractions result from temporary or permanent dipoles in molecules. There are three intermolecular forces: Dispersion forces Dipole forces Hydrogen bonds © 2011 Pearson Education, Inc. Chapter 13

Dispersion Forces Dispersion forces, or London forces, are the result of a temporary dipole. Electrons are constantly shifting, and a region may become temporarily electron poor and slightly positive, while another region becomes slightly negative. This creates a temporary dipole, and two molecules with temporary dipoles are attracted to each other. © 2011 Pearson Education, Inc. Chapter 13

Dispersion Forces, Continued Dispersion forces are the weakest intermolecular force. Dispersion forces are present in all molecules. The strength of the dispersion forces in a molecule is related to the number of electrons in the molecule: The more electrons in a molecule, the stronger the dispersion forces. © 2011 Pearson Education, Inc. Chapter 13

Dipole Forces Polar molecules have a permanent dipole. The oppositely charged ends of polar molecules are attracted to each other; this is the dipole force. The strength of a dipole force is typically 10% of a covalent bond’s strength. Dipole forces are stronger than dispersion forces. © 2011 Pearson Education, Inc. Chapter 13

Hydrogen Bonds Hydrogen bonds are a special type of dipole attraction. Hydrogen bonds are present when a molecule has an N—H, O—H, or F—H bond. Hydrogen bonds are especially important in water and living organisms. © 2011 Pearson Education, Inc. Chapter 13

Physical Properties of Liquids There are four physical properties of liquids that we can relate to the intermolecular attractions present in molecules: Vapor pressure Boiling point Viscosity Surface tension © 2011 Pearson Education, Inc. Chapter 13

Vapor Pressure At the surface of a liquid, some molecules gain enough energy to escape the intermolecular attractions of neighboring molecules and enter the vapor state. This is evaporation. The reverse process is called condensation. When the rates of evaporation and condensation are equal, the pressure exerted by the gas molecules above a liquid is called the vapor pressure. © 2011 Pearson Education, Inc. Chapter 13

Vapor Pressure, Continued The stronger the intermolecular forces between the molecules in the liquid, the less molecules that escape into the gas phase. As the attractive force between molecules increases, vapor pressure decreases. © 2011 Pearson Education, Inc. Chapter 13

Vapor Pressure Comparison Let’s compare water and ether. Water has strong intermolecular attractions, and ether has weak intermolecular attractions. At 0 C, neither has a significant vapor pressure. At 35 C, ether has a significant vapor pressure and water does not. © 2011 Pearson Education, Inc. Chapter 13

Vapor Pressure Versus Temperature As the temperature increases, the vapor pressure of a liquid increases. Again, the stronger the intermolecular attractions, the lower the vapor pressure at a given temperature. © 2011 Pearson Education, Inc. Chapter 13

Boiling Point The normal boiling point of a substance is the temperature at which the vapor pressure is equal to the standard atmospheric pressure. As we saw in the previous graph, the stronger the intermolecular attractions, the higher the boiling point of the liquid. A liquid with a high boiling point has a low vapor pressure. © 2011 Pearson Education, Inc. Chapter 13

Viscosity The viscosity of a liquid is a liquid’s resistance to flow. Viscosity is the result of an attraction between molecules. The stronger the intermolecular forces, the higher the viscosity. © 2011 Pearson Education, Inc. Chapter 13

Surface Tension The attraction between molecules at the surface of a liquid it called surface tension. For an object to sink in a liquid, it must first break through the surface. The stronger the intermolecular attractions, the stronger the surface tension of a liquid. © 2011 Pearson Education, Inc. Chapter 13

Properties of Solids Unlike gases, solids do not respond dramatically to temperature and pressure changes. We can study the solid state and make five general observations. Solids have a fixed shape and volume. Unlike liquids, solids are rigid. Solids are either crystalline or noncrystalline. Crystalline solids contain particles in a regular, repeating pattern. © 2011 Pearson Education, Inc. Chapter 13

Properties of Solids, Continued Solids do not compress or expand to any degree. Assuming there is no change in physical state, temperature and pressure have a negligible effect on the volume of a solid. Solids have a slightly higher density than their corresponding liquid. One important exception is water; ice is less dense than liquid water. Solids do not mix by diffusion. The particles are not free to diffuse in a solid heterogeneous mixture. © 2011 Pearson Education, Inc. Chapter 13

Crystalline Solids There are three types of crystalline solids, examples of which are shown below: Ionic solids, such as NaCl Molecular solids, such as S8 Metallic solids, such as Cu Crystalline network solids, such as diamonds © 2011 Pearson Education, Inc. Chapter 13

Ionic Solids A crystalline ionic solid is composed of positive and negative ions arranged in a regular, repeating pattern. In table salt, NaCl, sodium ions and chloride ions are arranged in a regular three-dimensional structure referred to as a crystal lattice. Other ionic compounds will have different crystal lattices. © 2011 Pearson Education, Inc. Chapter 13

Molecular Solids A crystalline molecular solid has molecules arranged in a particular conformation. In sulfur, S8, the molecules are arranged in a regular three-dimensional structure. Other examples of crystalline molecular solids are table sugar, C12H22O11, and water, H2O. © 2011 Pearson Education, Inc. Chapter 13

Metallic Solids A crystalline metallic solid is composed of metal atoms arranged in a definite pattern. A metallic crystal is made up of positive metal ions surrounded by valance electrons. Metals are good conductors of electricity because electrons are free to move about the crystal. This is referred to as the “electron sea” model. © 2011 Pearson Education, Inc. Chapter 13

Diamond Diamond is a special type of crystalline solid that has covalent bonds between large numbers of atoms. This type of crystalline solid is referred to as a network solid. Diamond is very hard and has a very high melting point. © 2011 Pearson Education, Inc. Chapter 13

General Properties of Solids © 2011 Pearson Education, Inc. Chapter 13

Structure of Water Let’s start with the electron dot formula for water. Water has a bent molecular shape and the bond angle is 104.5. Water is a polar molecule that exhibits strong hydrogen bonding. © 2011 Pearson Education, Inc. Chapter 13

Chemical Properties of Water Water can undergo an electrolysis reaction to produce hydrogen and oxygen: 2 H2O(l) → 2 H2(g) + O2(g) Water reacts with active metals to produce hydrogen and a metal hydroxide: 2 K(s) + 2 H2O(l) → 2 KOH(aq) + H2(g) Water reacts with metal oxides to produce a base: CaO(s) + H2O(l) → Ca(OH)2(aq) Water reacts with nonmetal oxides to produce an acid: CO2(g) + H2O(l) → H2CO3(aq) © 2011 Pearson Education, Inc. Chapter 13

Reactions that Produce Water Water is obtained as a product in several types of chemical reactions. Combustion reactions: 2 C2H2 (g) + 5 O2 (g) → 4 CO2 (g) + 2 H2O (g) C2H5OH (g) + 3 O2 (g) → 2 CO2 (g) + 3 H2O (g) Neutralization reactions: H3PO4 (aq) + 3 LiOH (aq) → Li3PO4 (aq) + 3 H2O (l) Dehydration reactions: Water is driven off from a hydrate by heating. © 2011 Pearson Education, Inc. Chapter 13

Hydrates A hydrate is a crystalline ionic compound that contains water: CuSO4  5 H2O The dot indicates that water molecules are bonded directly to each unit of hydrate. Heating a hydrate drives off the water and produces an anhydrous compound (without water). CuSO4  5 H2O(s) → CuSO4(s) + 5 H2O(l) heat © 2011 Pearson Education, Inc. Chapter 13