Chem chap 10

Condensed states

liquids and solids

Intermolecular forces

relatively weak interactions that occur between molecules

Dipole-dipole attraction

the attractive force resulting when polar molecules line up so that the positive and negative ends are close to each other

Hydrogen bonding

unusually strong dipole-dipole attractions that occur among molecules in which hydrogen is bonded to a highly electronegative atom

London dispersion forces

the forces, existing among noble gas atoms and nonpolar molecules, that involve an accidental dipole that induces a momentary dipole in a neighbor

Surface tension

the resistance of a liquid to an increase in its surface area

Capillary action

the spontaneous rising of a liquid in a narrow tube

Viscosity

the resistance of a liquid to flow

Crystalline solid

a solid with a regular arrangement of its components

Amorphous solid

a solid with considerable disorder in its structure

Lattice

a three-dimensional system of points designating the positions of the centers of the components of a solid (atoms, ions, or molecules)

Unit cell

the smallest repeating unit of a lattice

X-ray diffraction

a technique for establishing the structure of crystalline solids by directing X rays of a single wavelength at a crystal and obtaining a diffraction pattern from which interatomic spaces can be determined

Ionic solid

a solid containing cations and anions that dissolves in water to give a solution containing the separated ions, which are mobile and thus free to conduct an electric current

Molecular solid

a solid composed of neutral molecules at the lattice points

Atomic solid

a solid that contains atoms at the lattice points

Hexagonal closest packed (hcp) structure

a structure composed of closest packed spheres with an ababab arrangement of layers; the unit cell is hexagonal

Cubic closest packed (ccp) structure

a solid modeled by the closest packing of spheres with an abcabc arrangement of layers; the unit cell is face-centered cubic

Band model

a molecular model for metals in which the electrons are assumed to travel around the metal crystal in molecular orbitals formed from the valence atomic orbitals of the metal atoms

Molecular orbital (MO) model

a model that regards a molecule as a collection of nuclei and electrons, where the electrons are assumed to occupy orbitals much as they do in atoms, but having the orbitals extend over the entire molecule. In this model the electrons are assumed to be delocalized rather than always located between a given pair of atoms

Alloy

a substance that contains a mixture of elements and has metallic properties

Network solid

an atomic solid containing strong directional covalent bonds

Silica

the fundamental silicon-oxygen compound, which has the empirical formula SiO2, and forms the basis of quartz and certain types of sand

Silicate

salts that contain metal cations and polyatomic silicon- oxygen anions that are usually polymeric

Glass

an amorphous solid obtained when silica is mixed with other compounds, heated above its melting point, and then cooled rapidly

Ceramic

a nonmetallic material made from clay and hardened by firing at high temperature; it contains minute silicate crystals suspended in a glassy cement

Semiconductor

a substance conducting only a slight electric current at room temperature, but showing increased conductivity at higher temperatures

Vaporization (evaporation)

the change in state that occurs when a liquid evaporates to form a gas

Heat of vaporization

the energy required to vaporize one mole of a liquid at a pressure of one atmosphere

Condensation

the process by which vapor molecules re-form a liquid

Vapor pressure

the pressure of the vapor over a liquid at equilibrium

Sublimation

the process by which a substance goes directly from the solid to the gaseous state without passing through the liquid state

Heating curve

a plot of temperature versus time for a substance where energy is added at a constant rate.

Enthalpy (heat) of fusion

the enthalpy change that occurs to melt a solid at its melting point

Normal melting point

the temperature at which the solid and liquid states have the same vapor pressure under conditions where the total pressure on the system is one atmosphere

Normal boiling point

the temperature at which the vapor pressure of a liquid is exactly one atmosphere

Supercooled

the process of cooling a liquid below its freezing point without its changing to a solid

Superheated

the process of heating a liquid above its boiling point without its boiling

Phase diagram

a convenient way of representing the phases of a substance in a closed system as a function of temperature and pressure

Triple point

the point on a phase diagram at which all three states of a substance are present

Critical temperature

the temperature above which vapor cannot be liquefied no matter what pressure is applied

Critical pressure

the minimum pressure required to produce liquefaction of a substance at the critical temperature

Critical point

the point on a phase diagram at which the temperature and pressure have their critical values; the endpoint of the liquid-vapor line