Chapter Nine 1 States of Matter and Intermolecular Forces Chapter Eleven

Chapter Nine 2 ___________ ______ (bonds) govern molecular properties such as molecular geometries and dipole moments. ______________ _____ determine the macroscopic physical properties of liquids and solids. This chapter: –describes changes from one state of matter to another. –explores the types of intermolecular forces that underlie these and other physical properties of substances. Chapter Preview (page 433)

Chapter Nine 3 Molecular Forces Compared Figure 11.1 (page 434)

Chapter Nine 4 States of Matter Compared Intermolecular forces are of little significance; why? Intermolecular forces must be considered. Intermolecular forces are very important. Figure 11.2 (page 434)

Chapter Nine 5 Phase Changes Vaporization and Condensation (page 435) _____________ is the conversion of a liquid to a gas, l  g, this is a process. (Later we will have _____) The ________ __ ___________ (  H vapn ) is the quantity of heat that must be absorbed to vaporize a given amount of liquid at a constant temperature. The heat associated with the process of vaporization. _______________ is the reverse of vaporization. So many things in chemistry occur in opposites. The ________ __ __________ (  H condn ) accompanies this change of a gas to a liquid, ______. Enthalpy is a function of state: therefore, if a liquid is vaporized and the vapor condensed at constant temperature, the total  H must be zero:  H vapn +  H condn = 0  H condn = –  H vapn  Note the sign change

Chapter Nine 6 page 435

Chapter Nine 7 Problem 17: How much heat, in kilojoules, is required to vaporize3.530 kg of octane, C 8 H 18 ? Answer:

Chapter Nine 8 Vapor Pressure The ______ _________ of a liquid is the partial pressure exerted by the vapor when it is in dynamic equilibrium with the liquid at a constant temperature. _________ LiquidVapor __________ I remember hearing about this in Chapter 5

Chapter Nine 9 Liquid–Vapor Equilibrium More vapor forms; rate of condensation of that vapor increases … … until __________ is attained. Figure 11.3 (page 437)

Chapter Nine 10 Boiling Point and Critical Point _______ ____: the temperature at which the vapor pressure of the liquid equals the external pressure. _______ _______ _____: boiling point at 1 atm. Critical temperature (T c ): the highest temperature at which a liquid can exist. The critical pressure, P c, is the vapor pressure at the critical temperature. The condition corresponding to a temperature of T c and a pressure of P c is called the critical point.

Chapter Nine 11 Phase Changes Involving Solids (page 442) _______ (fusion): transition of solid  liquid. _______ ______: temperature at which melting occurs. –Same as freezing point! _______________,  H fusion, is the quantity of heat required to melt a set amount (one gram, one mole) of solid. ______________: transition of solid  vapor. –Example: Ice cubes slowly “disappear” in the freezer. __________________,  H subln, is the sum of the enthalpies of fusion and vaporization. ______ ____: all three phases—solid, liquid, vapor—are in equilibrium.

Chapter Nine 12 ** This is what happens to a snowball in Hades ** The temperature of the solid _________ as it is heated … Figure 11.8 (page 444) Supercooled snowball Below freezing We are heating a solid: q = We are at the _______ ____. The temperature of the solid remains ________ until the melting is complete. We have a phase change, s  l q = We are heating a liquid: q =

Chapter Nine 13 ** Phase Diagrams (page 445) ** A ______ _________ is a graphical representation of the conditions of ___________ __ _______ under which a substance exists as a solid, liquid, a gas, or some combination of these in equilibrium. A—B, solid-vapor equilibrium. _____ phases exist on this line. A—D, solid-liquid equilibrium. _____ phases exist on this line. A—C, liquid-vapor equilibrium. _____ phases exist on this line. Triple point. All three phases, s, l, g, are in equilibrium at this point.

Chapter Nine 14 ** Phase Diagram for H 2 O ** Figure (page 447)

Chapter Nine 15 ** Intermolecular Forces (page 450) ** … are forces _______ molecules. They _________ melting points, freezing points, and other _________ __________. Types of intermolecular forces include: ____________ (aka London) forces Dispersion forces arise because the electron cloud is not perfectly uniform. Tiny, momentary dipole moments can exist even in nonpolar molecules. ______________ forces. In molecules with permanent dipoles _________________ (a special type of dipole-dipole force)

Chapter Nine 16 ** Dispersion Forces Illustrated ** At a given instant, electron density, even in a nonpolar molecule like this one, is ___ __________ ________. The region of (_____________) higher electron density attains a small (–) charge … When another nonpolar molecule __________ … … the other end of the molecule is slightly (+).

Chapter Nine 17 … this molecule _________ a tiny dipole moment … … in this molecule. Opposite charges ________. This is the ____________ _____ of attraction known as the ____________ (London) force.

Chapter Nine 18 Strength of Dispersion Forces Dispersion force strength depends on ______________: the ease with which the electron cloud is distorted by an external electrical field. The ________ the polarizability of molecules, the _________ the dispersion forces between them. Polarizability in turn depends on molecular size and shape. Heavier molecule => more electrons => a more- polarizable molecule.

Chapter Nine 19 ** Dipole–Dipole Forces ** A ______ _______ has a positively charged “end” (δ+) and a negatively charged “end” (δ–). When molecules come close to one another, repulsions occur between like-charged regions of dipoles. Opposite charges tend to attract one another. The more polar a molecule, the more pronounced is the effect of dipole–dipole forces on physical properties.

Chapter Nine 20 ** Dipole–Dipole Interactions (page 452) ** __________ attract!

Chapter Nine 21 ** Hydrogen Bonds (page 454) ** A _________ ______ is an intermolecular force in which: –a _________ ____ that is covalently bonded to a (small, electronegative) nonmetal atom in one molecule … –is simultaneously attracted to a (small, electronegative) nonmetal atom of a neighboring molecule. Y ––– H Z ~~~~ When Y and Z are small and highly electronegative (__________) … … this force is called a ________ ____; a special, ______ type of dipole– dipole force.

Chapter Nine 22 ** Hydrogen Bonds in Water ** Figure (page 455)

Chapter Nine 23 Hydrogen Bonding in Acetic Acid Hydrogen bonding occurs __________ molecules.

Chapter Nine 24 A strong intermolecular force—the ________ _____ forms when a H atom covalently bonded to an O, a N, or a F atom of one molecule is simultaneously attracted to an O, a N, or a F atom of another molecule. _________ ________ accounts for some of the unusual properties of water (for example, an unusually high boiling point and the fact that the density of liquid water is greater than the density of ice). ________ _______ also governs aspects of the behavior of biological molecules such as proteins and the nucleic acids. _________ _____ also accounts for the fact that …..

Chapter Nine 25 **Problem 55:** Arrange the following substances in the expected order of increasing boiling point: H 2 O, NH 3, CH 4, CH 3 CH 3. Give the reason for your ranking. Answer: CH 4 and CH 3 CH 3 are nonpolar. Only weak dispersion forces NH 3 has a higher non-boiling point than CH 3 CH 3 despite ethane’s higher molecular mass, because of hydrogen bonding. In H 2 O, hydrogen bonding is stronger still.

Chapter Nine 26 Liquids and Intermolecular Forces (page 459) Much behavior and many properties of liquids can be attributed to intermolecular forces. ________ ________ (  ) is the amount of work required to extend a liquid surface and is usually expressed in J/m 2. ________ _____ are intermolecular forces between unlike molecules. _________ ______ are intermolecular forces between like molecules. A _________ is the interface between a liquid and the air above it. _________ is a measure of a liquid’s __________ to flow.

Chapter Nine 27 Surface Tension Molecules within the bulk of a liquid are attracted to more neighboring molecules than are _______ molecules. Figure (page 459)

Chapter Nine 28 Meniscus Formation Water wets the glass (__________ ________) and its attraction for glass forms a concave- up surface. What conclusion can we draw about the ________ ____ in mercury?

Chapter Nine 29 Comparing Viscosity The flow of the oil is started at the same time. Which oil flows more readily? Which oil has stronger intermolecular forces between its molecules? Oil is mostly hydrocarbons; what kind of forces are these? Figure (page 461) Highly viscous Less viscous

Chapter Nine 30 Types of Solids Amorphous solids have no significant long-range order. Crystalline solids have atoms/ions/molecules arranged in a regular pattern. Types of crystalline solids include: –Molecular solids, containing molecules held to one another by dispersion/dipole–dipole/ hydrogen bonding forces. –________ (covalent) solids. –_____ solids. –_______ solids (metals).

Chapter Nine 31 ** Network Covalent Solids ** (page 462) Network solids have a network of covalent bonds that extend throughout the solid, holding it firmly together. The allotropes of carbon provide good examples. __________ – Two or more forms of an element that differ in their basic molecular structure. Carbon Allotropes –_______ has each carbon bonded to four other carbons in a tetrahedral arrangement using sp 3 hybridization. –_______ has each carbon bonded to three other carbons in the same plane using sp 2 hybridization. –__________ are roughly spherical collections of carbon atoms in the shape of a soccer ball. –A _________ can be thought of as a plane of graphite rolled into a tube.

Chapter Nine 32 _________: Allotrope of carbon Three-dimensional network of ____ hybridized carbon atoms. Extremely strong, rigid. _________: Allotrope of carbon Three-dimensional network of ____ hybridized carbon atoms. Forces _______ layers are relatively weak.

Chapter Nine 33 Ionic Bonds as “Intermolecular” Forces (page 464) There are no molecules in an ionic solid, and therefore there can’t be any intermolecular forces. The attractions are electrostatic interionic attractions. _______ ____ (Chapter 9) is a measure of the strength of interionic attraction. The attractive force between a pair of oppositely charged ions _________: –as the ________ on the ions ________. –as the ionic radii _________. Lattice energies increase accordingly.

Chapter Nine 34 Interionic (between ions) Forces of Attraction Melting point of NaCl is about 801 o C. Mg 2+ and O 2– have much stronger forces of attraction for one another than do Na + and Cl –. Melting point of MgO is about 2800 o C. Figure (page 465)

Chapter Nine 35 Crystal Lattices (page 466) To describe crystals, three-dimensional views must be used. The repeating unit of the lattice is called the _____ _____. There are a number of different types of unit cell; hexagonal, rhombic, cubic, etc. The three types of _____ unit cells are: simple cubic, body-centered cubic (bcc), face-centered cubic (fcc).

Chapter Nine 36 Cubic Unit Cells Figure (page 467) The unit cell is a ____ in each case. Whole atoms shown for clarity. simple body-centered face-centered cubic cubic cubic

Chapter Nine 37 Unit Cells – Coordination Number The ____________ ______ is the number of nearest neighbor particles to a single particle in the crystal In a ______ ____ structure, the coordination number is __ (__ nearest neighbors)

Chapter Nine 38 1.___________ - 1 Atom at each of the corners of a cube. These atoms are shared equally with adjacent unit cells. The coordination number is 6. (8 corners) (1/8 atom at corner) = 1 atom/unit cell 2._________________ - 1 atom at each of the corners of a cube. These atoms are shared equally with adjacent unit cells, plus 1 atom in the center. The coordination number is 8. (8 corners) (1/8 atom at corner) + 1 atom in center = 2 atoms/unit cell 3._________________ - 1 atom at each of the corners of a cube. These atoms are shared equally with adjacent unit cells plus 1 atom at each of the 6 faces of the cube. The coordination number is 12. (8 corners) (1/8 atom at corner) + (6 faces) (1/2 atom/face) = 4 atoms/unit cell

Chapter Nine 39 Close-Packed Structures A _____ _______ structure in two dimensions. Figure (page 468)

Chapter Nine 40 Sum and Substance A ________, when repeated in three dimensions, generates the entire crystal lattice. Unit cell properties and dimensions, often measured by X- ray crystallography, can be used to find atomic radii and the densities of crystalline substances. The crystal structures of metals can be described as the packing of spheres. The two types of close-packing of spheres, ___________ _______ ______ (hcp) and _______________ (ccp), both reduce to the smallest possible fraction the volume occupied by holes or voids.