Solids, Liquids, Solids, Liquids, Gases (and Gases (and Solutions)Solutions)

Three Phases of Matter

Phase Differences

SolidSolid – definite volume and shape; particles packed in fixed positions; particles are not free to moveLiquidLiquid – definite volume but indefinite shape; particles close together but not in fixed positions; particles are free to move

GasGas – neither definite volume nor definite shape; particles are at great distances from one another; particles are free to move

A Molecular Comparison A Molecular Comparison of Liquids and Solidsof Liquids and Solids

Phase ChangesPhase Changes

Energy Changes Accompanying Phase Changes

• Sublimation: Hsub > 0 (endothermic).

• Vaporization: Hvap > 0 (endothermic).

• Melting or Fusion: Hfus > 0 (endothermic).

• Deposition: Hdep < 0 (exothermic).

• Condensation: Hcon < 0 (exothermic).

• Freezing: Hfre < 0 (exothermic).

Phase ChangesPhase Changes

Energy Changes Accompanying Phase Changes

• All phase changes possible under right conditions.

heat solid melt heat liquid boil heat gas= endothermic

cool gas condense cool liquid freeze cool solid= exothermic

Phase ChangesPhase Changes

Phase DiagramPhase DiagramRepresents phases as a function of temperature Represents phases as a function of temperature &pressure.&pressure.

Triple point: Triple point: Where all three lines meet, a unique combination of temperature and pressure where all three phases are in equilibrium together. That's why it is called a triple point.

Critical point Critical point Critical temperature: Critical temperature: above the critical temperature, it is impossible to condense a gas into a liquid just by increasing the pressure (the minimum temperature for liquefying a gas using pressure)

Critical pressure : Critical pressure : pressure required for liquefaction

Phase ChangesPhase Changes

Carbon dioxideCarbon dioxide CarbonCarbondioxidedioxide

WaterWaterWaterWater

CarbonCarbonCarbonCarbon

Types of SolidsTypes of SolidsCrystalline Solids: highly regular Crystalline Solids: highly regular

arrangement of their components [table arrangement of their components [table salt (NaCl), pyrite (FeSsalt (NaCl), pyrite (FeS22)].)].

Representation of Components Representation of Components in a Crystalline Solidin a Crystalline Solid

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

Ionic Solids

Ionic Solids• Ions (spherical) held together by electrostatic forces of

attraction.• There are some simple classifications for ionic lattice

types.

Bonding in SolidsBonding in Solids

Covalent-Network Solids• ALL COVALENT BONDS.• Atoms held together in large networks.

• Examples: diamond, graphite, quartz (SiO2), silicon carbide (SiC), and boron nitride (BN).

• In diamond: – each C atom is tetrahedral; there is a three-dimensional array of

atoms.

– Diamond is hard, and has a high melting point (3550 C).

Bonding in SolidsBonding in Solids

Network Atomic SolidsNetwork Atomic SolidsSome covalently bonded substances DO NOT form separate molecules.

Diamond, a network of covalently bonded carbon atoms

Graphite, a network of covalently bonded carbon atoms

Amorphous Amorphous solidssolids

considerable considerable disorder in disorder in their structures their structures (glass and (glass and plastic).plastic).

Metallic Solids• Problem: the bonding is too strong for London dispersion

and there are not enough electrons for covalent bonds.• Resolution: the metal nuclei float in a sea of electrons.• Metals conduct because the electrons are delocalized and

are mobile.

Bonding in SolidsBonding in Solids

MetalsMetals

Closest Packing Closest Packing of of

Atoms Atoms

Metal AlloysMetal Alloysare solid are solid solutionssolutions

Substitutional Substitutional Alloy: some Alloy: some metal atoms metal atoms replaced by replaced by others of similar others of similar size.size.

brass = Cu/Znbrass = Cu/Zn

Metal AlloysMetal Alloys(continued)(continued)

Interstitial Alloy:Interstitial Alloy: Interstices (holes) Interstices (holes) in in closest packed closest packed metal structure are metal structure are occupied by occupied by smallsmall atoms.atoms.

• steel = iron + carbonsteel = iron + carbon

Molecular Molecular SolidsSolidsStrong covalent forces within molecules

Weak covalent forces between molecules

Sulfur, SSulfur, S88 Phosphorus, PPhosphorus, P44

Molecular Solids• Intermolecular forces: dipole-dipole, London dispersion

and H-bonds.• Weak intermolecular forces give rise to low melting

points.• Room temperature gases and liquids usually form

molecular solids and low temperature.• Efficient packing of molecules is important (since they

are not regular spheres).

Bonding in SolidsBonding in Solids

Intermolecular ForcesIntermolecular Forces

Dipole-dipole attractionDipole-dipole attractionHydrogen bondsHydrogen bondsDispersion forcesDispersion forces

Forces of attraction between different molecules rather than bonding forces within the same molecule.

Hydrogen Bonding

Intermolecular ForcesIntermolecular Forces

Dipole-Dipole Forces

Intermolecular ForcesIntermolecular Forces

London Dispersion Forces• One instantaneous dipole can induce another

instantaneous dipole in an adjacent molecule (or atom).• The forces between instantaneous dipoles are called

London dispersion forces.

Intermolecular ForcesIntermolecular Forces

London Dispersion Forces

Intermolecular ForcesIntermolecular Forces

Forces and States of MatterForces and States of MatterAt STP, substances withAt STP, substances with o very weak intermolecular attraction very weak intermolecular attraction

= gases= gaseso strong intermolecular attraction strong intermolecular attraction

= liquids= liquidso very strong intermolecular attraction very strong intermolecular attraction

or ionic attraction or ionic attraction = solids= solids

Bonding in SolidsBonding in Solids

Classification of MatterClassification of MatterSolutions are homogeneous mixtures

SoluteSoluteA solute is the dissolved substance in a solution.

A solvent is the dissolving medium in a solution.

SolvenSolventt

Salt in salt water Sugar in soda drinks

Carbon dioxide in soda drinks

Water in salt water Water in soda

Dissolution of sodium ChlorideDissolution of sodium Chloride

Concentrated vs. DiluteConcentrated vs. Dilute

Some Properties of a LiquidSome Properties of a LiquidSurface TensionSurface Tension: :

The resistance to an The resistance to an increase in its increase in its surface area (polar surface area (polar molecules, liquid molecules, liquid metals).metals).

Capillary ActionCapillary Action: : Spontaneous rising Spontaneous rising of a liquid in a of a liquid in a narrow tube.narrow tube.

Surface Tension

Some Properties of a LiquidSome Properties of a Liquid

ViscosityViscosity: Resistance : Resistance to flowto flow

High viscosityHigh viscosity is is an an

indication of indication of strong strong

intermolecularintermolecular forces forces