Structure 1 - Models of the particulate nature of matter
Structure 1 builds the particle model that underpins all of chemistry. The exam tests your ability to link macroscopic observations, symbols and particle-level explanations: states and phase changes, atomic structure and isotopes, electron configuration, the mole and ideal gases.
Particles, states and amount
- Particles are in constant random motion; temperature measures average kinetic energy.
- Heating curves plateau at melting and boiling because energy overcomes intermolecular forces rather than raising kinetic energy.
- n = m/M and n = N/N_A, with N_A = 6.02 × 10²³ mol⁻¹. One mole of ideal gas occupies 22.7 dm³ at 273 K and 100 kPa.
- PV = nRT requires P in Pa, V in m³ and T in K; R = 8.31 J K⁻¹ mol⁻¹.
Atoms and electrons
- Isotopes differ in neutrons; relative atomic mass is the weighted mean of isotope masses.
- A mass spectrometer ionises, accelerates, deflects and detects; deflection depends on mass-to-charge ratio.
- Aufbau, Pauli and Hund rules give configurations. 4s fills before 3d but is written after it; Cr and Cu are exceptions.
- Line spectra reveal quantised levels; convergence corresponds to ionisation.
Worked example
2.45 g of a gas occupies 1.20 dm³ at 100 kPa and 298 K. n = PV/RT = (100 × 1.20)/(8.31 × 298) = 0.0485 mol. M = 2.45/0.0485 = 50.5 g mol⁻¹. kPa with dm³ works because R = 8.31 kPa dm³ K⁻¹ mol⁻¹.
Traps
- Using °C or cm³ without converting.
- Forgetting that 4s electrons are removed first in transition-metal ions.
- Treating a plateau as a kinetic-energy increase.