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: Chapter 13 1 © 2011 Pearson Education, Inc. 1. Liquids have a variable shape, but a fixed volume. 2. Liquids usually flow readily. 3. Liquids do not compress or expand significantly. 4. Liquids have a high density compared to gases. 5. Liquids that are soluble mix homogeneously.

Intermolecular Bond Concept An intermolecular bond is an attraction between molecules, whereas an intramolecular bond is between atoms in a molecule. Intermolecular bonds are much weaker than intramolecular bonds. Some properties of liquids are determined by the strength of attraction between molecules, such as: vapor pressure and boiling point viscosity, surface tension. Chapter 13 2 © 2011 Pearson Education, Inc.

Intermolecular Bonds There are three intermolecular forces: 1. Dispersion forces or London forces: they are weak forces, specially important in non-polar molecules. 2. Dipole forces: relatively strong, exist in polar molecules. 3. Hydrogen bonds: they are very strong, exist in molecules containing N-H, O-H, and F-H bonds. Chapter 13 3 © 2011 Pearson Education, Inc.

Chapter 13 Dispersion forces, or London forces, are the result of a temporary dipole. Thus they are weak forces. Electrons are constantly shifting, and a region may become temporarily electron poor and slightly positive, while another region becomes slightly negative. 4 © 2011 Pearson Education, Inc. The more electrons in a molecule, the stronger the dispersion forces. Two molecules with temporary dipoles are attracted to each other Dispersion Forces

Chapter 13 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. 5 © 2011 Pearson Education, Inc. Dipole Forces

Hydrogen Bonds Chapter 13 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. 6 © 2011 Pearson Education, Inc.

Physical Properties of Liquids There are four physical properties of liquids that we can relate to the intermolecular attractions present in molecules: 1.Vapor pressure 2.Boiling point 3.Viscosity 4.Surface tension Chapter 13 7 © 2011 Pearson Education, Inc.

Vapor Pressure When the rates of evaporation and condensation are equal, the pressure exerted by the gas molecules above a liquid is called the vapor pressure. 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. Chapter 13 8 © 2011 Pearson Education, Inc.

Chapter 13 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. 9 © 2011 Pearson Education, Inc. Vapor Pressure (Continued)

Vapor Pressure Versus Temperature Chapter 13 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. 10 © 2011 Pearson Education, Inc.

Boiling Point (Bp) The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid The normal boiling point of a substance is the temperature at which the vapor pressure is equal to the standard atmospheric pressure. Chapter © 2011 Pearson Education, Inc. 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.

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. Chapter © 2011 Pearson Education, Inc.

Surface Tension The attraction between molecules at the surface of a liquid is 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. Chapter © 2011 Pearson Education, Inc.

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. 1. Solids have a fixed shape and volume. 2. Solids are either crystalline or noncrystalline. Chapter © 2011 Pearson Education, Inc. 3. Solids do not compress or expand to any degree. 4. Solids have a slightly higher density than their corresponding liquid. 5. Solids do not mix by diffusion.

Crystalline Solids There are three types of crystalline solids, examples of which are shown below: 1.Ionic solids, such as NaCl 2.Molecular solids, such as S 8 3.Metallic solids, such as Cu 4.Crystalline network solids, such as diamonds Chapter © 2011 Pearson Education, Inc.

Ionic Solids Chapter 13 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. 16 © 2011 Pearson Education, Inc.

Molecular Solids Chapter 13 A crystalline molecular solid has molecules arranged in a particular conformation. In sulfur, S 8, the molecules are arranged in a regular three-dimensional structure. Other examples of crystalline molecular solids are table sugar, C 12 H 22 O 11, and water, H 2 O. 17 © 2011 Pearson Education, Inc.

Metallic Solids Chapter 13 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. 18 © 2011 Pearson Education, Inc.

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. Chapter © 2011 Pearson Education, Inc.

Changes in Physical State Heat is necessary to raise the temperature and change the physical state of a substance. Specific heat is the amount of heat required to raise 1.00 g of a substance 1  C. Water is the reference and its specific heat is 1.00 cal/(g x  C). The specific heat of ice is 0.50 cal/(g x  C) and of steam is 0.48 cal/(g x  C). They are about half that of liquid water. Chapter © 2011 Pearson Education, Inc.

Solid–Liquid Phase Changes As a solid melts, the temperature is constant until all of the solid is changed to liquid. The amount of heat required to melt 1.00 g of substance is called the heat of fusion (H fusion ). For water, the heat of fusion is 80.0 cal/g. When a liquid changes to a solid, the heat change is the heat of solidification (H solid ). The value of H fusion is the same as the value of H solid. Chapter © 2011 Pearson Education, Inc.

Liquid–Gas Phase Changes As a liquid vaporizes, the temperature is constant until all of the liquid is changed to gas. The amount of heat required to vaporize 1.00 g of substance is called the heat of vaporization (H vapor ). For water, the value is 540 cal/g. When a gas changes to a liquid, the heat change is the heat of condensation (H cond ). The value of H vapor is the same as the value of H cond. Chapter © 2011 Pearson Education, Inc.

Solid–Gas Phase Changes Some substances convert directly between the solid and gas phases. The process of a solid changing directly to a gas is called sublimation. The process of a gas changing directly to a solid is called deposition. Carbon dioxide (CO 2 ) and iodine (I 2 ) are two common substances that undergo sublimation–deposition phase changes. Chapter © 2011 Pearson Education, Inc.

Temperature–Energy Graphs Chapter 13 We can graph the amount of energy required to change the temperature and physical state of a substance. The heating curve for water is shown here. As energy is added, the temperature increases and changes the physical state. 24 © 2011 Pearson Education, Inc.

Energy from Heating Curves We can use the heating curve and heat values for water to calculate how much energy is required to change the temperature of a sample of water. The amount of energy required to raise the temperature of a substance is calculated using the following formula: The amount of energy required to change the state of a substance is calculated as follows: Chapter © 2011 Pearson Education, Inc.

Energy Calculation How much energy is required to raise 25.5 g of ice at –5.0  C to steam at  C? Chapter © 2011 Pearson Education, Inc.

Energy Calculation How much energy is required to raise 25.5 g of ice at –5.0  C to steam at  C? Looking at the heating curve for water, there are four regions: 1.Heating of solid ice from –5.0  C to 0.0  C. 2.Melting of ice at 0.0  C. 3.Heating of liquid water from 0.0  C to  C. 4.Vaporization of water at  C. Chapter © 2011 Pearson Education, Inc.

Energy Calculation, Continued The total energy is the sum of the energy in Steps 1 through 4. Calculate the energy for each step. 1.(25.5 g) x [0.0 – (–5.0)]  C x (0.50 cal/g x  C) = 64 cal 2.(25.5 g) x (80.0 cal/g) = 2040 cal 3.(25.5 g) x [100.0 – 0.0)]  C x (1.00 cal/g x  C) = 2550 cal 4.(25.5 g) x (540 cal/g) = 13,800 cal Chapter 13 The total energy is: 64 cal cal cal cal = 18,500 cal. 28 © 2011 Pearson Education, Inc.

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

Properties of Ice Water is one of the few substances that is less dense as a solid than as a liquid. As water freezes, the hydrogen bonds organize the water molecules into a three-dimensional structure where the molecules are farther apart then in the liquid. Chapter 13 Liquid water has a density of 1.00 g/mL, while ice has a density of g/mL. 30 © 2011 Pearson Education, Inc.

Water Purification In many areas, water has lots of dissolved minerals leading to high concentrations of ions. This is referred to as hard water. It is often not suitable for use in agriculture or drinking. The water is purified in a water softener by exchanging the cations and anions for H + ions and OH – ions. Chapter © 2011 Pearson Education, Inc.

Physical Properties of Water Chapter 13 Water has unusual melting and boiling points, especially compared to the other hydrogen compounds of Group VIA/16. This is due to hydrogen bonding that is present in water, but not present in H 2 S, H 2 Se, or H 2 Te. 32 © 2011 Pearson Education, Inc.

Chemical Properties of Water Water can undergo an electrolysis reaction to produce hydrogen and oxygen: 2 H 2 O(l) → 2 H 2 (g) + O 2 (g) Water reacts with active metals to produce hydrogen and a metal hydroxide: 2 K(s) + 2 H 2 O(l) → 2 KOH(aq) + H 2 (g) Water reacts with metal oxides to produce a base: CaO(s) + H 2 O(l) → Ca(OH) 2 (aq) Water reacts with nonmetal oxides to produce an acid: CO 2 (g) + H 2 O(l) → H 2 CO 3 (aq) Chapter © 2011 Pearson Education, Inc.

Reactions that Produce Water Water is obtained as a product in several types of chemical reactions. –Combustion reactions: 2 C 2 H 2 (g) + 5 O 2 (g) → 4 CO 2 (g) + 2 H 2 O (g) C 2 H 5 OH (g) + 3 O 2 (g) → 2 CO 2 (g) + 3 H 2 O (g) –Neutralization reactions: H 3 PO 4 (aq) + 3 LiOH (aq) → Li 3 PO 4 (aq) + 3 H 2 O (l) –Dehydration reactions: Water is driven off from a hydrate by heating. Chapter © 2011 Pearson Education, Inc.

Hydrates A hydrate is a crystalline ionic compound that contains water: CuSO 4  5 H 2 O 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). CuSO 4  5 H 2 O(s) → CuSO 4 (s) + 5 H 2 O(l) Chapter 13 heat 35 © 2011 Pearson Education, Inc.