Chapter 14 Chapter 14 Liquids and SolidsLiquids and Solids

Three types of bonding Three types of bonding between atoms between atoms

Covalent – electrons shared between Covalent – electrons shared between nonmetal atoms, forms molecules or nonmetal atoms, forms molecules or covalent crystal lattice structures such covalent crystal lattice structures such as diamond (covalent network solid)as diamond (covalent network solid)Ionic bonds – transfer of electrons Ionic bonds – transfer of electrons between metals and nonmetals, forms between metals and nonmetals, forms ionic crystal lattice structures (ionic solid)ionic crystal lattice structures (ionic solid)Metallic bonds – group sharing of Metallic bonds – group sharing of loosely held electrons of metals, These loosely held electrons of metals, These electrons can migrate throughout the electrons can migrate throughout the metal.metal.

Highest Boiling Point – crystal lattice Highest Boiling Point – crystal lattice structures (ionic or covalent)structures (ionic or covalent)

Lowest Boiling Points – molecular Lowest Boiling Points – molecular compoundscompounds

Crystal lattice structuresCrystal lattice structures

DiamondDiamond

Salt Salt

Molecular compoundsMolecular compounds

Molecules attracted to each other Molecules attracted to each other by:by:– Hydrogen bonding (strongest)Hydrogen bonding (strongest)– Dipole-dipole attraction (next Dipole-dipole attraction (next

strongest)strongest)– Dispersion forces (weakest, Dispersion forces (weakest,

therefore lowest boiling point)therefore lowest boiling point)

Hydrogen bondingHydrogen bonding

The hydrogen of one molecule is The hydrogen of one molecule is “semi-bonded” to a non-bonding “semi-bonded” to a non-bonding pair of electrons of another pair of electrons of another molecule.molecule.

Requirements for Requirements for hydrogen bondhydrogen bond

1.1. molecule must have hydrogenmolecule must have hydrogen

2.2. molecule must have a molecule must have a non-bonding pair of valence non-bonding pair of valence electrons (check electron-dot electrons (check electron-dot structure)structure)

HF, HHF, H22O, NHO, NH33 all have hydrogen all have hydrogen

bonding, strongest intermolecular bonding, strongest intermolecular force (high melting points)force (high melting points)

Dipole-Dipole ForcesDipole-Dipole Forces

Is the attraction of the positive Is the attraction of the positive side of one molecule to the side of one molecule to the negative side of another molecule. negative side of another molecule.

Molecule must have a dipole for Molecule must have a dipole for this to occur this to occur

For dipole must haveFor dipole must have– Polar covalent bondPolar covalent bond– A geometry that allows for a dipoleA geometry that allows for a dipole

Dispersion ForcesDispersion Forces

Attraction between non-polar Attraction between non-polar molecules that have a temporary molecules that have a temporary dipoledipoleCreated by a temporary induced Created by a temporary induced warping of the electron cloud. warping of the electron cloud. Also called London dispersion Also called London dispersion forces or van der Waals forces forces or van der Waals forces Is weakest of all intermolecular Is weakest of all intermolecular forces (very low boiling points)forces (very low boiling points)

Change of stateChange of state

A liquid boils when the vapor A liquid boils when the vapor pressure (partial pressure) is pressure (partial pressure) is equal the atmospheric pressure. equal the atmospheric pressure.

Boiling can be thought of as Boiling can be thought of as internal evaporation. internal evaporation.

For a bubble to form internally For a bubble to form internally it must be able to overcome it must be able to overcome atmospheric pressure.atmospheric pressure.

Water can be made to boil at a Water can be made to boil at a lower temperature by decreasing lower temperature by decreasing the pressure above it. the pressure above it.

Triple point – temperature and Triple point – temperature and pressure at which a substance will pressure at which a substance will exist as a solid, liquid and a gas at exist as a solid, liquid and a gas at the same time. the same time.

Phase diagram of waterPhase diagram of water

Phase-change graphPhase-change graph

Bonds and energyBonds and energy

Breaking molecular or weak bonds Breaking molecular or weak bonds between molecules always takes between molecules always takes energy.energy.The formation of any bond always The formation of any bond always gives off energy.gives off energy.At high temps there is enough At high temps there is enough energy in the system so bonds energy in the system so bonds cannot form. (different temps for cannot form. (different temps for different bonds)different bonds)

AssignmentAssignment

Page 492 and 493 questions Page 492 and 493 questions 3, 4, 8, 9 – 13, 15, 17, 20, 21, 3, 4, 8, 9 – 13, 15, 17, 20, 21, 24, 25, 28, 30, 31, 3324, 25, 28, 30, 31, 33