Trace how the scientific model of the atom changed from Dalton through the modern quantum mechanical model, and explain what evidence drove each change.
The idea that matter is made of atoms is ancient, but the atom as a scientific model is built from evidence, and it changed every time new evidence demanded it. John Dalton (early 1800s) proposed that all matter is made of tiny, indivisible atoms, that atoms of one element are identical and different from atoms of other elements, and that atoms combine in whole-number ratios to form compounds -- a solid atom, like a tiny billiard ball.
J.J. Thomson (1897) discovered the electron using a cathode-ray tube, proving atoms are not indivisible after all -- they contain smaller, negatively charged particles. He proposed the "plum pudding" model: a positively charged sphere with electrons scattered through it like fruit in a pudding. Ernest Rutherford (1911) shattered that model with his gold foil experiment: he fired positively charged particles at thin gold foil, and while most passed straight through, a small number bounced almost straight back. That could only happen if the atom was mostly empty space with a tiny, dense, positively charged nucleus at its center.
Niels Bohr (1913) proposed that electrons orbit the nucleus in fixed energy levels, like planets in specific lanes, and that electrons absorb or release energy only in fixed amounts when jumping between levels -- this explained the specific colors of light atoms emit. The modern quantum mechanical model (1920s onward) refined this further: electrons do not travel in neat orbits at all, but exist in orbitals, three-dimensional regions of space where an electron is likely to be found. Each model was not a mistake being corrected out of nowhere -- it was the best explanation for the evidence available at the time, replaced only when new evidence demanded a better one.
Mastery looks like: They can describe each major atomic model in the correct order, and explain what specific evidence caused each change.
Common stumbles: Listing the models as trivia without connecting each one to its supporting evidence; assuming the modern model is "the atom finally figured out completely" rather than the current best-supported explanation.