Topic 4 - Intermolecular Forces and States of Matter: States of Matter

States of Matter - Factors

Almost all matter exists in three classical states: solid, liquid, gas.
The state depends on:

1. Temperature (thermal energy available).

2. Pressure (external force per unit area).

3. Intermolecular forces (IMFs) between atoms, ions, and/or molecules.

Solids - Definition

Condensed phase of matter that is ordered.

Solids - Particle Arrangement

Atoms/ions/molecules are closely packed, usually in a lattice.

Solids - Motion

Particles vibrate but are largely immobile.

Solids - Properties

• Definite shape and volume.

• Generally rigid and resistant to compression.

• Wide variation in melting point, hardness, electrical conductivity, depending on bonding/IMFs.

Solids - Types

• Ionic solids (e.g., NaCl) → high melting points, brittle, conduct electricity when molten.

• Covalent network solids (e.g., diamond, SiO₂) → very hard, high melting point, poor conductors (except graphite).

• Metallic solids → good conductors, malleable, variable hardness.

• Molecular solids (e.g., ice, I₂) → lower melting points, soft, depend strongly on IMFs.

Liquids - Definition

Condensed phase of matter but disordered.

Special note: Liquids exist only within certain temperature-pressure ranges

Liquids - Particle Arrangement

Molecules are close enough for IMFs to hold them together, but not fixed in place.

Liquids - Properties

• Definite volume, but no fixed shape (takes container shape).

• Fluidity → particles can slide past each other.

• Physical properties depend on IMFs:

  • Viscosity → resistance to flow.

  • Surface tension → energy required to increase surface area (important in capillary action).

  • Vapour pressure → tendency of molecules to escape into gas phase.

Gases - Definition

Uncondensed, disordered phase of matter.

Gases - Particle Arrangement

Atoms/molecules are far apart, in constant, random motion.

Gases - Properties

• No fixed shape or volume; expand to fill any container.

• Generate pressure via collisions with container walls.

• IMFs are extremely weak/negligible due to large separations.

Gases - Variables

• n = number of particles (mol).

• V = volume (L or m³).

• P = pressure (Pa, kPa, atm).

• T = temperature (K, °C).

Boyle’s Law (P-V relationship)

P ∝ 1\V (at constant T, n)

Charles’ Law (V-T Relationship)

V ∝ T (at constant P, n)

Guy-Lussac’s Law (P-T Relationship)

P ∝ T (at constant V, n)

Avogadro’s Law (V-n Relationship)

V ∝ n (at constant P, T)

Ideal Gas Law - Formula

PV = nRT

Ideal Gas Law - Gas Constant (R)

R (Gas constant): depends on units:

• 8.314 J/mol K (SI units).

• 0.0821 atm/mol K (lab units).

Ideal Gas Law - Assumptions

• Negligible intermolecular forces.

• Negligible molecular volume.

Ideal Gas Law - Limitations

Assumptions fail at high pressures (molecules close together) and low temperatures (IMF significant)

Dalton’s Law of Partial Pressure

• For an ideal mixture, identity of gas doesn’t matter, only the total number of particles (moles).

• Dalton’s Law of Partial Pressures: P_total = P_A + P_B + ...

  • Where P_A and P_B are the partial pressures of gases A and B.

Mole Fraction (χ)

• A way to express the composition of a mixture based on how many moles of each component it contains.

• χ_A = n_A/n_total

  • n_A​ = moles of gas A

  • n_total = ∑n_i = total moles of all gases

• P_A = χ_A ⋅ P_total

Plasma

A fourth state of matter, occurs at very high temperatures when atoms are ionized (e.g., stars, lightning).

Phase Changes

Transitions between states (melting, freezing, evaporation, condensation, sublimation, deposition) depend on IMFs and energy input/output.