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3.3Properties of Substances and Mixtures

Solids, Liquids, and Gases — AP CHEMISTRY Revision Notes & Topical Questions

5 min read 10 parts Lesson 7 of 20 1 quiz

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3.3 Solids, Liquids, and Gases — Notes — AP CHEMISTRY notes: Describe the particle arrangement and motion in solids, liquids and gases and the factors that determine the state of a substance.Particles are closely packed in fixed positions and vibrate.Solids have a fixed shape and…

  • Vapour pressure
  • Boiling point
  • Crystalline solid
  • Amorphous solid
  • Sublimation
  • Compressibility

Section 1 of 10Solids

Solids
Particles are closely packed in fixed positions and vibrate.
Solids have a fixed shape and volume and are very hard to compress.
Solids may be crystalline (regular arrangement) or amorphous (no regular arrangement), but in both the motion of individual particles is limited.

Section 2 of 10Liquids

1
Particles are close together and in contact, continually moving and colliding, and able to move past one another.
2
Liquids have a fixed volume, take the shape of the container, and are almost incompressible.
3
Particle arrangement and movement depend on the nature and strength of the intermolecular forces, such as polarity and hydrogen bonding.
4
Solids and liquids typically have similar molar volumes because particles are in close contact in both.

Section 3 of 10Gases

Gases
Particles are far apart relative to their size, in constant rapid random motion.
Collision frequency and average spacing depend on temperature, pressure and volume.
Intermolecular forces have a minimal effect, so gases have no fixed shape or volume and are highly compressible.
PropertySolidLiquidGas
Particle spacingCloseCloseFar apart
MotionVibrateSlide past each otherFast, random
CompressibilityNoneAlmost noneHigh
DensityHighHighLow

Section 4 of 10What decides the state

  • The state depends on the balance between the kinetic energy of the particles (proportional to temperature) and the strength of the forces holding them together.

Section 5 of 10Phase changes

1
Melting, vaporisation and sublimation are endothermic because energy is absorbed to overcome intermolecular forces.
2
Freezing, condensation and deposition are exothermic.
3
During a phase change at constant pressure the temperature stays constant.
  • The energy supplied changes potential energy (particle separation), not average kinetic energy.
4
Vaporisation needs more energy than melting.

Section 6 of 10Vapour pressure and boiling point

Vapour pressure
Vapour pressure the pressure of vapour in dynamic equilibrium with its liquid in a closed container at a given temperature.
Weaker intermolecular forces give a higher vapour pressure and lower boiling point.
Boiling point
Boiling point the temperature at which vapour pressure equals external pressure; the normal boiling point is at 1 atm.

Section 7 of 10Intermolecular forces and shape

1
Dispersion forces exist in all molecules and increase with electrons and polarisability.
2
Dipole-dipole forces act between polar molecules.
3
Hydrogen bonding occurs for H bonded to N, O or F.
4
Ion-dipole forces act between ions and polar molecules.
5
Linear n-pentane boils higher than branched neopentane because of greater surface contact.

Section 8 of 10More from the specification

More from the specification
Crystalline lattice structures in engineered alloys
  • Crystalline lattice structures in engineered alloys combining complementary metals into uniform alloys provides a structural means to improve tensile strength.
Covalent bond
  • A shared pair of electrons between two atoms, giving noble gas configurations.
Ionic solid
  • Lattice of alternating cations and anions.
Network solid
  • Covalent bonds extend through the whole crystal.
Valence electrons
  • Electrons in the outer shell.
Silicon dioxide
  • A giant covalent compound found in sand and quartz.
Nonpolar molecule
  • A molecule with no net dipole.
Diamond
  • A very hard form of carbon.
Alloy
  • A mixture of a metal with one or more other elements.

Section 9 of 10Key terms

TermMeaning
Crystalline solidSolid with a regular three-dimensional arrangement.
Amorphous solidSolid without regular arrangement.
Vapour pressurePressure of vapour in equilibrium with its liquid.
Boiling pointTemperature at which vapour pressure equals external pressure.
SublimationDirect change from solid to gas.
CompressibilityEase with which volume can be reduced by pressure.

Section 10 of 10Exam technique

1
Saying temperature rises during a phase change — it stays constant
2
Saying liquids have no fixed volume — liquids have fixed volume but no fixed shape
3
Treating melting as exothermic — it absorbs energy
4
Saying stronger intermolecular forces give a higher vapour pressure — they give a lower one

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