1.4. STATES OF MATTER

What are ideal gases and their key assumptions?

• Definition: Ideal gases follow the kinetic theory of gases, making them a theoretical model for gas behavior.

• Assumptions:

  1. Gas molecules move fast and randomly.

  2. Molecules have zero volume.

  3. Molecules experience no intermolecular forces (attraction or repulsion).

  4. Collisions are elastic (no kinetic energy loss).

  5. Temperature is related to the average kinetic energy of molecules.

What is the ideal gas equation, and how is it used?

• Formula: pV = nRT

  • p = pressure (Pa)

  • V = volume (m³)

  • n = number of moles of gas (mol)

  • R = gas constant (8.31 J K⁻¹ mol⁻¹)

  • T = temperature (K)

  Applications:

• Calculate volume of gas:

  Rearrange formula to V = nRT/p.

• Calculate molar mass (Mr):

  Rearrange formula to n = pV/RT, then calculate Mr = mass/moles.

What are key relationships in the behavior of gases?

• Boyle’s Law: Volume∝1Pressure (at constant temperature).

• Gay-Lussac’s Law: Pressure∝Temperature (at constant volume).

• Charles’ Law: Volume∝Temperature (at constant pressure).

What is the lattice structure of a simple molecular compound? (Examples: iodine, buckminsterfullerene C₆₀, ice)

• Simple Molecular Lattice:

  • Molecules held by weak intermolecular forces (e.g., London dispersion forces, hydrogen bonding).

• Examples:

  1. Iodine (I₂):

     • Simple molecular lattice with London dispersion forces between iodine molecules.

  2. Buckminsterfullerene (C₆₀):

     • A spherical structure with weak forces between C₆₀ molecules.

  3. Ice:

     • A lattice of water molecules held by hydrogen bonding.

What is the lattice structure of a giant molecular compound? (Examples: SiO₂, graphite, diamond)

• Giant Molecular Lattice:

  • Atoms are held together by strong covalent bonds in a 3D arrangement.

• Examples:

  1. Silicon(IV) Oxide (SiO₂):

     • A 3D tetrahedral network of Si and O atoms.

  2. Graphite:

     • Layers of carbon atoms bonded in hexagonal rings. Weak forces between layers allow them to slide.

  3. Diamond:

     • A rigid 3D network of carbon atoms bonded strongly

What is the lattice structure of a giant metallic compound? (Example: Copper)

• Giant Metallic Lattice:

  • Positive metal ions surrounded by a sea of delocalized electrons.

• Arrangement:

  • Metal ions packed in hexagonal layers or cubic arrangements.

  • Example: Copper:

    • Layers of copper ions with delocalized electrons allowing malleability and conductivity.

What are the physical properties of giant ionic structures? (Example: NaCl)

• Melting and Boiling Points: High, due to strong electrostatic forces.

• Electrical Conductivity: Conductive only when molten or in solution.

• Solubility: Soluble in water (forms ion-dipole bonds).

• Hardness: Hard but brittle.

What are the physical properties of simple molecular structures? (Example: I₂, C₆₀)

• Melting and Boiling Points: Low, due to weak intermolecular forces.

• Electrical Conductivity: Do not conduct electricity (no charged particles).

• Solubility: Insoluble unless polar or can form hydrogen bonds (e.g., NH₃).

• Hardness: Soft.

What are the physical properties of giant molecular structures? (Example: Diamond, graphite, SiO₂)

• Melting and Boiling Points: Very high, due to strong covalent bonds.

• Electrical Conductivity: Graphite conducts electricity (delocalized electrons), diamond and SiO₂ do not.

• Solubility: Insoluble in water.

• Hardness: Diamond and SiO₂ are hard, graphite is soft (weak forces between layers).

What are the physical properties of giant metallic structures? (Example: Copper)

• Melting and Boiling Points: Moderately high to high.

• Electrical Conductivity: Conducts electricity in solid and liquid states (mobile electrons).

• Solubility: Insoluble in water.

• Hardness: Hard and malleable (layers can slide over each other).

How can you deduce the type of structure and bonding from given information?

• Ionic Compound: High melting/boiling points, soluble, conducts electricity when molten or in solution.

• Simple Molecular: Low melting/boiling points, insoluble (unless polar), does not conduct electricity.

• Giant Molecular: Very high melting/boiling points, insoluble, mostly does not conduct electricity (except graphite).

• Metallic Compound: Moderately high melting/boiling points, conducts electricity, malleable.