Matter and Atomic Structure
What this domain tests
Matter and Atomic Structure tests particle theory, states of matter, atomic models, electron arrangement, isotopes and the Periodic Table, plus separation of mixtures.
Core rules
- Kinetic particle theory: particles in solids vibrate about fixed positions; liquids slide past each other; gases move randomly and are far apart.
- Heating a solid raises its temperature until the melting point, then temperature stays constant while latent heat breaks the forces between particles.
- An atom has protons and neutrons in the nucleus and electrons in shells. Proton number Z equals the number of protons; nucleon number A equals protons plus neutrons; neutrons = A − Z.
- Electrons fill shells in the order 2, 8, 8. The number of outer-shell electrons determines the group; the number of shells gives the period.
- Isotopes have the same proton number but different nucleon numbers. Elements contain one type of atom; compounds are chemically combined; mixtures are not.
- Separation: filtration for an insoluble solid, distillation for miscible liquids, chromatography for dyes, magnetism for magnetic materials.
Worked example
An atom has proton number 11 and nucleon number 23. Protons = 11, electrons = 11 because the atom is neutral, and neutrons = 23 − 11 = 12. The electron arrangement is 2, 8, 1: one outer electron means Group 1, and three shells mean Period 3. The element is sodium.
Traps
Do not use the nucleon number as the neutron number. Do not give an ion the same electron count as its neutral atom. Do not call air a compound. In distillation, state which liquid boils first and why.