Chap 10Liquids & Solids

Key termsMolecules – atoms joined by covalent bonds

(molecular compounds)

Condensed states – solid and liquid

Intramolecular forces – within the molecule

Intermolecular forces – between molecules

Intermolecular Forces• Known as IMFs• Arise from unequal distribution of electrons in

atoms and the attraction of opposites• Contribute to properties of the molecules

o Melting & boiling points(lower mp or bp = weaker IMFs)

o Bonding(type of bond affects IMFs)

o Vapor pressures(higher IMFs = lower vapor pressure)

o Dissolving process – making solutions

• strongest = H Bonding; weakest = London Dispersion • strongest = solids; weakest = gases

Types of Intermolecular Forces

Dipole-Dipole Forces – forces between polar moleculesmolecules with dipoles attract each other• line up so positive and negative ends are close• molecules arrange to maximize interactions• Hydrogen bonding – strong dipole-dipole

o H bonded to highly electronegative atom

London Dispersion Forces – forces between nonpolar molecules and Noble gases• Induce a dipole – polarizability – temporary dipole• Weak forces• Increase as size of atom increases

Interactions

• Dipole - dipole• Ion – dipole

o H-Bonding• Ion – ion

o Ions only• Induced dipole – induced dipole

o London dispersion only

LiquidsGeneral Properties:• Definite volume; indefinite shape• Molecules in constant motion – ability to flow• Low compressibility• Surface tension = resistance of a liquid to

increase its surface area• Capillary action = spontaneous rising of liquid up

narrow tubeo Cohesion – intermolecular forces among molecules within

the liquido Adhesion – forces between liquid molecules and container

• Viscosity = measure of a liquid’s resistance to flowo Higher IMF = higher viscosity

SolidsGeneral properties:• Definite shape; definite volume• Rigid structure/shape• Particles vibrate in place• 2 Types of solids:

o Crystalline solids – ionic & molecular compounds• Highly regular pattern/arrangement• Lattice = 3D arrangement showing positions of atoms• Unit cell = smallest repeating unit of the lattice• Determined through X-Ray diffraction

o Amorphous solids – mostly covalent • Random order/arrangement• EX: glass

• Network solids – large “giant” molecules• Called atomic solids• Tend to be brittle – due to directional bonds;

arrangement/structureo Rings = networks o Layers of atoms are weaker – gaps between layerso Stronger structure = all atoms bonded

• Refer to diamond vs graphite (p471)

Molecular Solids Ionic Solids

• Strong covalent bonding within molecule but weak between molecules

• Low melting points• Soft• Made of nonmetals

• Strong electrostatic forces between ions

• High melting points• Hard• Made of oppositely charged

ions

MetalsGeneral Properties:• Solids; good conductors; malleable; ductile;

high melting points• Metallic crystals

o Bonding is strong but non directional

• Ionic bond when metal to non-metal• “sea” of electrons when metal to metal• Mostly form alloys when combined

Phase Changes• aka changes of state• Vaporization or evaporation

o Enthalpy/heat of vaporization (∆Hvap) – energy needed to vaporize 1 mole of liquid at 1 atm.

o Endothermic processo Vapor pressure

• Condensation• Sublimation• Boiling• Melting

o Enthalpy/heat of fusion (∆Hfus) – energy change occurs at the melting point of a solid

• Freezingo Melting point and freeing point same

• Requires energy change for all - E = q=mC∆T

Vapor Pressure• Rates of condensation and evaporation are equal

= called equilibrium vapor pressure• No net change when two opposite processes

balance out• Vapor pressure increases as temperature

increases• Larger molecules tend to have lower vapor

pressure

Equation *(

Phase Diagram• Can show phases of materials as function of

temperature and pressure