Chemistry lab safety; atomic theory timeline

Follow chemistry lab safety and trace the atomic model from Dalton to Thomson, Rutherford, Bohr, and the quantum model. Dalton (1803): elements are made of atoms; atoms of an element are identical; compounds have fixed ratios. Thomson (1897) discovered the electron ("plum pudding" model); Rutherford (1911) gold foil showed a tiny, dense, positive nucleus; Bohr (1913) placed electrons in energy levels. Lab safety: goggles, closed shoes, tied hair, no food, know the SDS and eyewash, and never point a heated test tube at anyone. Rutherford fired alpha particles at gold foil: most passed straight through (atoms are mostly empty space), but about 1 in 8,000 bounced back sharply (a small, dense, positive nucleus). That result replaced Thomson's model. The modern quantum model describes electrons as probability clouds (orbitals), not fixed orbits. Each model was kept until new evidence required a change — that is how science works. Evidence: most alpha particles pass through; a few deflect sharply. Inference 1: atoms are mostly empty space. Inference 2: positive charge and mass are concentrated in a tiny nucleus. Conclusion: the nuclear model replaces the plum-pudding model. Make a timeline of five atomic models with the key experiment or evidence for each, and write a CER on why Rutherford rejected Thomson's model. Usual mistake: Treating older models as "wrong and useless" — each explained the evidence available at the time.