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3.2Properties of Substances and Mixtures

Properties of Solids — AP CHEMISTRY Revision Notes & Topical Questions

5 min read 11 parts Lesson 6 of 20 1 quiz

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3.2 Properties of Solids — Notes — AP CHEMISTRY notes: Explain the properties of ionic, covalent network, molecular and metallic solids using particles and forces.A crystalline solid has particles in a regular repeating three-dimensional lattice.An amorphous solid such as glass h…

  • Interstitial alloy
  • Substitutional alloy
  • Covalent network solid
  • Molecular solid
  • An amorphous solid such as glass has no long-range order and softens over a range of temperatures
  • Particle diagrams of interacting species help to explain macroscopic properties

Section 1 of 11Crystalline and amorphous solids

Crystalline and amorphous solids
A crystalline solid has particles in a regular repeating three-dimensional lattice.
An amorphous solid such as glass has no long-range order and softens over a range of temperatures.
Particle diagrams of interacting species help to explain macroscopic properties.

Section 2 of 11Ionic solids

1
Cations and anions are held by strong Coulombic attraction in a lattice.
2
They have low vapour pressures and high melting and boiling points.
3
They are hard but brittle, because shifting a layer brings like charges together.
4
They conduct only when molten or dissolved.

Section 3 of 11Covalent network solids

1
Atoms are joined in a continuous network of covalent bonds, formed only from nonmetals and metalloids.
2
Melting requires breaking covalent bonds, so melting points are very high.
3
Diamond is very hard; graphite is a network of two-dimensional layers.
4
They are generally poor conductors, except graphite, which has delocalised electrons.
5
Examples are diamond, graphite, SiO2 and Si.

Section 4 of 11Molecular solids

Molecular solids
They contain discrete molecules held by intermolecular forces (dispersion, dipole-dipole, hydrogen bonding).
Only intermolecular forces are overcome on melting, so melting points are low.
They are soft and do not conduct, for example I2, ice and sucrose.

Section 5 of 11Metallic solids

Metallic solids
They are lattices of metal cations in a sea of delocalised electrons.
Mobile electrons make them good electrical and thermal conductors.
Nondirectional bonding lets layers slide, so metals are malleable and ductile.

Section 6 of 11Alloys

Interstitial alloy
  • Interstitial alloy small atoms in lattice holes, such as carbon in iron (steel), giving a harder, less malleable material.
Substitutional alloy
  • Substitutional alloy similar-radius atoms replace host atoms, such as brass (Cu and Zn).

Section 7 of 11Comparing solids with Coulomb's law

1
Ionic lattices with higher ion charges and smaller radii have stronger attractions and higher melting points (MgO > NaCl, NaF > NaI).
2
For molecular solids, larger more polarisable electron clouds give stronger dispersion forces and higher melting points; I2 is a solid and F2 a gas at room temperature.
3
Weaker interparticle forces give higher vapour pressure, so I2 and solid CO2 sublime readily.
4
Name the particles and the specific force broken when comparing two solids.
SolidParticlesForcesMelting pointConducts
IonicIonsIonic bondsHighWhen molten or dissolved
MolecularMoleculesIntermolecular forcesLowNo
Covalent networkAtomsCovalent bondsVery highNo (graphite yes)
MetallicCations and electronsMetallic bondingVariesYes

Section 8 of 11Large molecules

  • In biomolecules and polymers, noncovalent interactions between or within molecules determine shape, and shape determines function.

Section 9 of 11More from the specification

1Metallic bonding in interstitial alloys
  • Metallic bonding in interstitial alloys mixing smaller metalloid atoms into host transition metals produces robust alloys, providing a means of hardening.
2Vapor pressure
  • The pressure exerted by a vapour over a liquid.
3Silicon dioxide
  • A giant covalent compound found in sand and quartz.
4Nonpolar molecule
  • A molecule with no net dipole.
5Liquid
  • A state with a fixed volume that flows, particles sliding past each other.
6Volume
  • The space taken up by an object.

Section 10 of 11Key terms

TermMeaning
Crystalline solidSolid with a regular repeating arrangement of particles.
Amorphous solidSolid with no long-range order.
Covalent network solidSolid with atoms joined throughout by covalent bonds.
Molecular solidSolid of discrete molecules held by intermolecular forces.
Metallic solidLattice of cations in a sea of delocalised electrons.
AlloyMixture of a metal with other elements retaining metallic properties.

Section 11 of 11Exam technique

1
Saying molecular solids melt by breaking covalent bonds — only intermolecular forces are overcome
2
Saying all covalent solids have low melting points — network solids have very high ones
3
Saying graphite does not conduct — it conducts through delocalised electrons
4
Naming the solid type without naming the force that is broken

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