Matter
Matter in NSSCO Chemistry tests the kinetic particle model, states and changes of state, purity and diffusion.
Particle model
Solids have particles closely packed in a regular arrangement, vibrating about fixed positions; liquids have particles close but irregular and able to slide; gases have widely spaced particles moving randomly at high speed. The kinetic particle model explains shape, volume, compressibility and diffusion. Heating increases kinetic energy; at melting and boiling points the temperature stays constant while energy overcomes forces between particles (latent heat), so a heating curve has flat plateaus.
Purity and diffusion
A pure substance melts and boils at a fixed temperature. An impurity usually lowers the melting point and raises the boiling point, giving a range. Diffusion is the random spreading of particles from high to low concentration; it is faster at higher temperature and for gases of lower relative molecular mass. Brownian motion of smoke or pollen grains is evidence for random particle motion.
Worked example
Ice at -10 °C is heated steadily. The temperature rises to 0 °C, then remains at 0 °C until all the ice has melted, then rises again. Reasoning: during melting, energy supplied is used to break the forces holding the lattice together, not to increase average kinetic energy, so the thermometer reading does not change. Once melting is complete, added energy increases kinetic energy and temperature.
Traps
Do not say particles expand when heated; the particles stay the same size and the spaces between them increase. Gas pressure comes from collisions of particles with the container walls, not from particles pushing each other. Evaporation occurs below the boiling point from the surface; boiling occurs throughout the liquid at a fixed temperature. An impure solid melts over a range, not at one sharp value.