Module 2.1 Matter
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Module 2 (Physics) is 32 questions for A and B3 and 52 for B1, B2 and B2L under EASA. 2.1 is a small but easy-scoring sub-module.
Knowledge levels
| Sub-module | A | B1 | B2 / B2L | B3 |
|---|---|---|---|---|
| 2.1 Matter | 1 | 2 | 2 | 1 |
Content: nature of matter (chemical elements, structure of atoms, molecules), chemical compounds, states (solid, liquid, gas) and changes between states.
Matter, elements and compounds
- Matter is anything that has mass and occupies space.
- An element is a substance made of one type of atom (about 118 known; e.g. H, O, Al, Fe, Ti, Cu).
- A compound is two or more elements chemically combined in fixed proportions (H₂O, Al₂O₃, NaCl). Its properties differ from those of its elements.
- A mixture is substances physically mixed, not chemically bonded, and separable by physical means (air, fuel blends).
- A molecule is the smallest particle of a substance that keeps its chemical properties (O₂, H₂O).
Structure of the atom
| Particle | Charge | Relative mass | Location |
|---|---|---|---|
| Proton | +1 | 1 | nucleus |
| Neutron | 0 | 1 | nucleus |
| Electron | −1 | about 1/1836 | shells (orbits) around the nucleus |
- Atomic number (Z) = number of protons; defines the element. In a neutral atom it also equals the number of electrons.
- Mass number (A) = protons + neutrons.
- Isotopes: same number of protons, different numbers of neutrons (e.g. hydrogen, deuterium, tritium).
- Ions: atoms that have gained electrons (negative ion, anion) or lost electrons (positive ion, cation).
Electron shells
Electrons fill shells K, L, M, N... The maximum per shell is 2n²: 2, 8, 18, 32. The outermost shell is the valence shell; its electrons decide chemical and electrical behaviour (see Module 3.1).
Key fact: An atom with a full valence shell (noble gases: helium, neon, argon) is chemically stable and almost never reacts.
Worked example
Aluminium has atomic number 13 and mass number 27. How many neutrons and how are its electrons arranged?
- Neutrons = 27 − 13 = 14
- Electrons = 13 → shells 2, 8, 3 (3 valence electrons)
Chemical bonding
| Bond | How | Example | Typical properties |
|---|---|---|---|
| Ionic | electrons transferred, ions attract | NaCl | high melting point, conducts when molten or dissolved |
| Covalent | electrons shared | H₂O, CO₂, diamond | often low melting point (molecular), poor conductor |
| Metallic | "sea" of free electrons around positive ions | Al, Cu, Fe | good conductors, malleable, ductile |
The free electrons of metallic bonding explain why metals conduct heat and electricity.
States of matter
| State | Shape | Volume | Particle behaviour |
|---|---|---|---|
| Solid | fixed | fixed | vibrate about fixed positions, strong forces |
| Liquid | takes container shape | fixed | close together but free to move |
| Gas | fills container | variable (compressible) | far apart, fast random motion |
Plasma (ionised gas) is sometimes called the fourth state (lightning, arcs).
Changes of state
| Change | Name | Heat |
|---|---|---|
| Solid → liquid | melting (fusion) | absorbed |
| Liquid → gas | evaporation / boiling (vaporisation) | absorbed |
| Gas → liquid | condensation | released |
| Liquid → solid | freezing (solidification) | released |
| Solid → gas | sublimation (e.g. dry ice, ice on a wing at low pressure) | absorbed |
| Gas → solid | deposition (frost on a cold surface) | released |
- During a change of state the temperature stays constant: the heat goes into breaking or forming bonds. This is latent heat (see 2.3 Thermodynamics).
- Boiling point falls when pressure falls: water boils below 100 °C at altitude. This matters for hydraulic fluid and fuel vapour lock.
- Evaporation cools the surface - the principle behind the vapour-cycle air-conditioning evaporator.
Key fact: Condensation and freezing release heat; melting, evaporation and sublimation absorb heat.
Why matter matters in maintenance
| Topic | Practical link |
|---|---|
| Valence electrons and metallic bonding | why copper and aluminium conduct (Module 3.1) and why corrosion is an electron-transfer process (Module 6.4) |
| Compounds | oxides (Al₂O₃ protects aluminium; iron oxide - rust - does not protect steel), salts in corrosion products |
| Changes of state | vapour lock in fuel lines, carburettor icing, the evaporator and condenser of vapour-cycle air conditioning, frost formation on parked aircraft |
| Gases | nitrogen in tyres and accumulators (inert, dry, does not support combustion), oxygen systems (Module 7.1 safety) |
| Ions | electrolytes in batteries (Module 3.5), ionisation in lightning and static discharge |
Worked example - counting particles
An oxygen atom has atomic number 8 and mass number 16. An O²⁻ ion has gained two electrons.
- Protons = 8, neutrons = 16 − 8 = 8
- Electrons in the neutral atom = 8 (shells 2, 6); in O²⁻ = 10 (shells 2, 8 - a full outer shell, which is why oxygen readily forms this ion)
Exam tips
- Do not confuse "atomic number" (protons) with "mass number" (protons + neutrons).
- Compounds have fixed proportions and new properties; mixtures do not.
- Questions often ask which particle carries no charge (neutron) or which is lightest (electron).