Germany Jahrgangsstufe 9 Chemistry
Chapters: 6
1. How chemists think and work
How chemists think and work
- The Scientific Method – The scientific method is the careful way scientists find out how the world works. Observe something, ask a testable question, make a hypothesis (a clear, testable guess), test it with a fair experiment (change one variable, measure one, keep the rest the same), repeat and record data, analyse it, draw a conclusion and share it so others can check. Results that fail the test are useful too: they send you back to a new hypothesis.
2. Substances, properties and the particle model
Substances, properties and the particle model
- The Particle Model of Matter – All matter is made of tiny particles that are always moving. In a solid they are close and only vibrate; in a liquid they are close but slide past each other; in a gas they are far apart and move fast in all directions. Heating gives particles more energy: either they move faster (temperature rises) or the forces between them are broken (the state changes while the temperature stays the same). Gas pressure comes from particles hitting the walls.
3. Chemical reactions and Dalton's atomic model
Chemical reactions and Dalton's atomic model
- Atoms and Molecules – In a chemical reaction mass is neither created nor destroyed (conservation of mass), and a compound always has its elements in the same ratio by mass (constant proportions). Dalton explained both: matter is made of tiny atoms that join in small whole numbers. Atoms join to form molecules; charged atoms or groups are ions. Formulae are written by crossing valencies. Molecular mass (or formula unit mass for ionic compounds) is the sum of the atomic masses in the formula, in u.
4. Compounds and the nucleus-shell atom model
Ions, salts, metals and the nuclear atom
- Ionic Compounds: How Metals and Non-metals React – A metal atom gives its outer electrons to a non-metal atom so that both get a full outer shell (octet). The metal becomes a positive ion (cation), the non-metal a negative ion (anion), and the strong pull between them is an ionic (electrovalent) bond. Ionic compounds are hard crystalline solids with high melting points, dissolve in water, and conduct electricity only when molten or dissolved.
5. Atomic structure and the periodic table
Energy levels and the short periodic table
- Structure of the Atom – An atom has a tiny, heavy, positive nucleus made of protons and neutrons. Electrons move around it in fixed shells K, L, M, N. The number of protons (Z) tells the element; protons + neutrons give the mass number (A). Outer electrons decide valency. Isotopes share Z; isobars share A.
6. Donor-acceptor: forming and discharging ions
Redox as electron transfer
- Oxidation and Reduction: Corrosion and Rancidity – Oxidation is gain of oxygen (or loss of hydrogen); reduction is loss of oxygen (or gain of hydrogen). They always happen together, so these are called redox reactions. The substance that gives oxygen is the oxidising agent; the one that takes it is the reducing agent. In daily life, oxidation causes corrosion (like rusting of iron) and rancidity (fats and oils going stale).