Inside the atom and through reactions. The nuclear atom and its electron shells explain the periodic table; atoms rearrange and are never lost, which is why mass is conserved and equations balance; and reactions happen when particles collide hard enough.
Each lesson works two ways. Students can work through the online tutorial at their own pace (it checks their answers and saves their progress in their browser), or you can teach it to the whole class from the slides, then send students into the tutorial for the Modify and Make steps.
Every lesson guide has plain-language notes, the answers to every check, a solution for every task, and slides and a worksheet for Waypoints Prepare. These guide pages are not linked from student pages, but they are not secret either: keep printed Teacher editions for answers you do not want students to find.
Protons, neutrons and electrons; atomic and mass numbers (AC9S9U06, Year 9).
The particles of Years 7 and 8 have parts. An atom has a tiny, dense nucleus of protons (charge +1, mass 1) and neutrons (no charge, mass 1), with electrons (charge −1, mass about 1/1840) around it.
Atoms of one element always have the same number of protons, but the neutrons can differ: these are isotopes (carbon-12, carbon-13, carbon-14). They have the same electrons, so they react alike. Some are stable; others are unstable (radioactive). The build board says which, for elements 1 to 20.
Some nuclei are unstable. They decay by giving out radiation, at random for one atom but predictably for many.
Decay chains (node 5) are a class task, with the decay board set to isotope: uranium-238.
Misconceptions: gamma makes a new element; the beta electron comes from the shells; alpha is always the least dangerous (it is the most damaging inside the body).
Each unstable nucleus decays at random, but a large sample halves in a fixed time, the half-life: 1/2, 1/4, 1/8 … Half-life is not changed by heat or chemistry. Short half-lives suit medicine (fluorine-18, about 2 hours); long ones suit dating (carbon-14, 5730 years).
Misconceptions: the sample is all gone after two half-lives; each nucleus decays at exactly the half-life; heating speeds decay up.
On screen: the short tutorials From uranium to lead (node 5 of 9U06, decay chains, in the atoms unit), Where does the mass go? (node 5 of 9U07, in equations) and Use the table to predict (node 4 of 10U06, in periodic) cover the integration nodes.
Optional ideas if you run a practical for this unit: pick one, adapt it to your equipment, or use your own.
These are models: school radioactive sources are tightly controlled, and none are needed.
Safety and ethics: collect stray marbles from the floor.
Reactions rearrange atoms; none are made or destroyed; balanced equations show it (AC9S9U07, Year 9).
In a chemical reaction the atoms of the reactants separate and join up in new arrangements, the products. The types and numbers of atoms do not change: only how they are joined. So the total mass does not change either (conservation of mass).
That is why an equation must balance: each side must show the same atoms. In methane burning, CH₄ + 2O₂ → CO₂ + 2H₂O, both sides have 1 C, 4 H and 4 O.
Before the atoms: a word equation names what reacts and what is made, reactants → products (methane + oxygen → carbon dioxide + water). The common slips are leaving out water when a fuel burns, leaving out oxygen, and putting heat or light in the equation. Word equations show no amounts or atoms; that is what formulas and balancing add.
When something burns in the open, gases (carbon dioxide, water vapour) escape into the air, so the ash weighs less than the wood. In a sealed container nothing escapes, and the mass stays the same. Rusting seems to gain mass because oxygen from the air joins the iron.
Optional ideas if you run a practical for this unit: pick one, adapt it to your equipment, or use your own.
Safety and ethics: safety glasses with vinegar; never cap a fizzing bottle, use a balloon. Gloves for steel wool.
Electron shells, and why elements in a group behave alike (AC9S10U06, Year 10).
Electrons fill shells in order: 2 in the first, 8 in the second, 8 in the third (then 2 more for potassium and calcium). The electrons in the outermost shell, the outer-shell electrons, decide how an element reacts.
Each period fills one shell, so the period number is the number of shells. Across a period the outer electrons rise from 1 to 8, then reset to 1 as a new shell starts: that is why properties repeat and groups behave alike. Across a period, elements change from metals to non-metals. The table board can be coloured by shells, outer electrons, or metal and non-metal (colour:).
Misconceptions: outer electrons keep counting past 8; periods and groups swapped; the table is ordered by mass.
Optional ideas if you run a practical for this unit: pick one, adapt it to your equipment, or use your own.
Safety and ethics: calcium gives off hydrogen and leaves an alkaline solution: small amounts, safety glasses, no flames nearby.
Particles must collide with enough energy to react: collision theory (AC9S10U07, Year 10).
Particles react only when they collide, and only if the collision has enough energy (the activation energy). Most collisions just bounce. The rate of a reaction depends on how many collisions happen each second and how many of those have enough energy.
| Change | What it does to collisions |
|---|---|
| Higher temperature | Particles move faster: more collisions, and many more with enough energy |
| Higher concentration | More particles in the same space: more collisions |
| Larger surface area (smaller pieces) | More particles exposed: more collisions |
| A catalyst | Gives the reaction an easier path with a lower activation energy: more collisions have enough energy. It is not used up. |
Temperature has the biggest effect because it changes both how often particles collide and how hard.
Synthesis (A + B → AB), decomposition (AB → A + B) and displacement (A + BC → AC + B, only when A is more reactive than B). Classify by the pattern; predict products from it.
Optional ideas if you run a practical for this unit: pick one, adapt it to your equipment, or use your own.
Safety and ethics: water no hotter than about 45 °C; safety glasses with vinegar.