CHAPTER 12 Liquids and Solids

Intermolecular Forces Forces of attraction between different molecules rather than bonding forces within the same molecule. Dipole-dipole attraction Hydrogen bonds Dispersion forces

Dipole-Dipole Attraction dipole-dipole attraction: molecules with dipoles orient themselves so that “+” and “-” ends of the dipoles are close to each other.

Dipole Forces

Hydrogen Bonding hydrogen bonds: dipole-dipole attraction in which hydrogen is bound to a highly electronegative atom. (F, O, N)

Hydrogen Bonding in Water

Hydrogen Bonding in DNA

London Dispersion Forces Dispersion forces: relatively weak forces caused by instantaneous dipole, in which electron distribution becomes asymmetrical. The ONLY forces of attraction that exist among noble gas atoms and nonpolar molecules. (Ar, C8H18)

London Dispersion Forces

Boiling point as a measure of intermolecular attractive forces

Some Properties of a Liquid Surface Tension: The resistance to an increase in its surface area (polar molecules, liquid metals).

Some Properties of a Liquid Capillary Action: Spontaneous rising of a liquid in a narrow tube.

Some Properties of a Liquid Viscosity: Resistance to flow (molecules with large intermolecular forces).

Types of Solids Crystalline Solids: highly regular arrangement of their components [table salt (NaCl), pyrite (FeS2)].

Types of Solids Amorphous solids: considerable disorder in their structures (glass).

Representation of Components in a Crystalline Solid Lattice: A 3-dimensional system of points designating the centers of components (atoms, ions, or molecules) that make up the substance.

Types of Crystalline Solids Ionic Solid: contains ions at the points of the lattice that describe the structure of the solid (NaCl).

Types of Crystalline Solids Molecular Solid: discrete covalently bonded molecules at each of its lattice points (sucrose, ice).

Packing in Metals Model: Packing uniform, hard spheres to best use available space. This is called closest packing. Each atom has 12 nearest neighbors.

Closest Packing Holes

Metal Alloys Substitutional Alloy: some metal atoms replaced by others of similar size. brass = Cu/Zn

Metal Alloys (continued) Interstitial Alloy: Interstices (holes) in closest packed metal structure are occupied by small atoms. steel = iron + carbon

graphite, diamond, ceramics, glass Network Solids Composed of strong directional covalent bonds that are best viewed as a “giant molecule”. brittle do not conduct heat or electricity carbon, silicon-based graphite, diamond, ceramics, glass

Sulfur – S8

Phosphorus – P4

Diamond

Graphite

Zirconia

Equilibrium Vapor Pressure The pressure of the vapor present at equilibrium. Determined principally by the size of the intermolecular forces in the liquid. Increases significantly with temperature. Volatile liquids have high vapor pressures.

LeChatelier’s Principle When a system at equilibrium is placed under stress, the system will undergo a change in such a way as to relieve that stress.

Translation: When you take something away from a system at equilibrium, the system shifts in such a way as to replace what you’ve taken away. When you add something to a system at equilibrium, the system shifts in such a way as to use up what you’ve added.

LeChatelier’s Example #1 A closed container of ice and water at equilibrium. The temperature is raised. Ice + Energy  Water The equilibrium of the system shifts to the _______ to use up the added energy. right

LeChatelier’s Example #2 A closed container of N2O4 and NO2 at equilibrium. NO2 is added to the container. N2O4 + Energy  2 NO2 The equilibrium of the system shifts to the _______ to use up the added NO2. left

LeChatelier’s Example #3 A closed container of water and its vapor at equilibrium. Vapor is removed from the system. water + Energy  vapor The equilibrium of the system shifts to the _______ to make more vapor. right

Water phase changes constant Temperature remains __________ during a phase change. constant Water phase changes

Kinetic Energy

Phase Diagram Represents phases as a function of temperature and pressure. Critical temperature: temperature above which the vapor can not be liquefied. Critical pressure: pressure required to liquefy AT the critical temperature. Critical point: critical temperature and pressure (for water, Tc = 374°C and 218 atm).

Water Water

Phase changes by Name

Carbon dioxide Carbon dioxide

Carbon Carbon

Sulfur