Energy and the States Energy and the States Of MatterOf Matter

Forces between particlesForces between particles

States of matterStates of matter

Changes in stateChanges in state

Learning objectivesLearning objectives

Describe types of motion in moleculesDescribe types of motion in molecules Distinguish among states of matter based Distinguish among states of matter based

on propertieson properties Describe four types of intermolecular forcesDescribe four types of intermolecular forces Identify main forces operating in simple Identify main forces operating in simple

substancessubstances Perform calculations of heat involved in Perform calculations of heat involved in

changes of statechanges of state

Atom motion and temperatureAtom motion and temperature

Atoms in molecules have three types of Atoms in molecules have three types of motionmotion Rotation – moving about the centre of massRotation – moving about the centre of mass Vibration – vibrating about the centre of massVibration – vibrating about the centre of mass Translation – movement of the centre of massTranslation – movement of the centre of mass

As temperature increases, the energies of As temperature increases, the energies of all types of motion increaseall types of motion increase

Three States of MatterThree States of Matter Solid: strong interactions Solid: strong interactions

Fixed shapeFixed shape Not compressibleNot compressible RigidRigid DenseDense

Liquid: medium interactionsLiquid: medium interactions

LiquidLiquid Not rigidNot rigid Assumes shape of containerAssumes shape of container Not compressibleNot compressible DenseDense

Gas: no interactionsGas: no interactions

Not rigidNot rigid Completely fills containerCompletely fills container CompressibleCompressible Low densityLow density

Plasma: the fourth statePlasma: the fourth state

At very high energies (temperatures) all the At very high energies (temperatures) all the electrons are removed from the atomselectrons are removed from the atoms

Not an important state for chemistryNot an important state for chemistry

May the force be with youMay the force be with you

Covalent and ionic bonds are the Covalent and ionic bonds are the intraintramolecular forces that hold the atoms in molecular forces that hold the atoms in molecules togethermolecules together

InterIntermolecular forces hold the molecules molecular forces hold the molecules togethertogether

Collectively, the intermolecular forces are Collectively, the intermolecular forces are called called van der Waalsvan der Waals forces forces

All arise from electrostatic interactionsAll arise from electrostatic interactions

Intermolecular forcesIntermolecular forces

Polar molecules experience strong intermolecular Polar molecules experience strong intermolecular interactions due to existence of positive and interactions due to existence of positive and negative ends of dipolesnegative ends of dipoles

Weaker forces exist between nonpolar molecules. Weaker forces exist between nonpolar molecules. These are due to fluctuations in the electron These are due to fluctuations in the electron distributions in the molecules which create distributions in the molecules which create momentary (weak) dipoles – London forcesmomentary (weak) dipoles – London forces

Intermolecular interactions are known collectively Intermolecular interactions are known collectively as as van der Waals van der Waals forcesforces

Name of forceName of force OriginOrigin StrengthStrength

Ion-dipoleIon-dipole Between ions and Between ions and moleculesmolecules

Quite strong (10 – Quite strong (10 – 50 kJ/mol)50 kJ/mol)

Dipole-dipoleDipole-dipole Between Between permanent dipolespermanent dipoles

Weak (3 – 4 Weak (3 – 4 kJ/mol)kJ/mol)

Hydrogen bondsHydrogen bonds Polar bonds with H Polar bonds with H and (O,N)and (O,N)

Quite strong (10 – Quite strong (10 – 40 kJ/mol)40 kJ/mol)

London London dispersion dispersion forcesforces

Fluctuating dipoles in Fluctuating dipoles in non-polar bondsnon-polar bonds

Weak (1 – 10 Weak (1 – 10 kJ/mol)kJ/mol)

The Four Forces of the ApocalypseThe Four Forces of the Apocalypse

Hydrogen bonding: something about Hydrogen bonding: something about waterwater

High boiling point High boiling point compared with similar compared with similar compoundscompounds Liquid at earth temperatureLiquid at earth temperature

Solid less dense than Solid less dense than liquidliquid Essential for life on earthEssential for life on earth

High heat capacityHigh heat capacity Modifying influence on Modifying influence on

climateclimate

Universal solventUniversal solvent

Hydrogen bondingHydrogen bonding

The ultimate expression of polarityThe ultimate expression of polarity Small positive H atom exerts strong Small positive H atom exerts strong

attraction on O atomattraction on O atom Other H-bonding molecules: HF, NHOther H-bonding molecules: HF, NH33

HH22O is the supreme example: two H atoms O is the supreme example: two H atoms

and two lone pairs per moleculeand two lone pairs per molecule

HH22O has optimum combination of O has optimum combination of

lone pairs and H atomslone pairs and H atoms

CompoundCompound Number of lone Number of lone pairspairs

Number of H Number of H atomsatoms

HFHF 33 11

HH22OO 22 22

NHNH33 11 33

H bonding generates three-H bonding generates three-dimensional networkdimensional network

Ice floats!Ice floats!

Something so familiar we might believe all Something so familiar we might believe all solids float on their liquids. Not so. Water is solids float on their liquids. Not so. Water is the exception.the exception.

Hydrogen bonding and lifeHydrogen bonding and life

hold the two strands of the DNA double helix hold the two strands of the DNA double helix together together

hold polypeptides together in such secondary hold polypeptides together in such secondary structures as the alpha helix and the beta structures as the alpha helix and the beta conformationconformation

help enzymes bind to their substratehelp enzymes bind to their substrate help antibodies bind to their antigen help antibodies bind to their antigen help transcription factors bind to each otherhelp transcription factors bind to each other help transcription factors bind to DNA help transcription factors bind to DNA

Implications for life on earth Implications for life on earth

Without H-bonds Without H-bonds molecules like DNA molecules like DNA would not existwould not exist

H-bonds hold the two H-bonds hold the two strands togetherstrands together

Comparative Comparative weakness of bonding weakness of bonding allows for DNA allows for DNA replicationreplication dna

Intermolecular forces determine Intermolecular forces determine physical propertiesphysical properties

Strong ionic bonds Strong ionic bonds mean high melting mean high melting pointpoint

Dipole-dipole Dipole-dipole interactions – much interactions – much lower melting pointslower melting points

Dispersion forces only Dispersion forces only – very low melting – very low melting pointspoints