Chapter 3 told you matter is built from elements. This chapter opens the element up and asks what is inside — and finds that a single number decides the answer.
An atom has three kinds of particle in it — protons, neutrons and electrons. Change the number of each and something different happens every time, and the pattern is worth learning before any of the detail:
Almost every question in this chapter is one of those three, in disguise.
It was once widely believed that all matter was made of water, wood, air, fire, earth and metal. Better technology let scientists find evidence for what matter is really built from — and the models they drew kept being revised as that evidence arrived. That story of revision is itself examinable.
This is scoped for G3, so the early atomic models and the mass of an atom — which the textbook marks optional for G2 — are core here. Relative atomic mass from isotope abundance goes beyond the printed pages, but it is in Iz's class notes, so it has a lesson of its own.
Cutting wood down to cellulose to carbon. A million atoms across a hair — and the nanotechnology that works at that scale.
Start → Lesson 2Protons, neutrons and electrons; the planetary model and the two models it replaced. Build an atom and watch its identity change.
Start →Why no two elements can share a proton number, how Mendeleev built the table, and how new elements are made.
Start → Lesson 4Same protons, different neutrons. Then the calculation from your notes: why chlorine's mass is 35.5 and not a whole number.
Start →Labelled circles, and the difference between a molecule of an element and a molecule of a compound. Build your own.
Start → Lesson 6Reading subscripts, counting atoms, and telling an element from a compound by the formula alone.
Start →Every definition, the sub-atomic particle table, the isotope rules, the RAM calculation and all the applications.
Open → PracticeLabel the atom, type nucleon numbers, calculate a relative atomic mass — every wrong answer explains itself.
Practice → Challenging · Lvl 2Twenty harder questions with the options set deliberately close together — only correct reasoning separates them.
Take it on →