Summary
Highlights
Scientists have always been curious about the structure of atoms. Early models included John Dalton's, which described atoms as tiny, unchanging, indestructible spheres. However, the discovery of positive and negative electrical charges led to new models. Thomson proposed the "plum pudding model," where a positive mass contained embedded negative electrons, leading to a neutral atom.
Ernest Rutherford conducted a groundbreaking experiment using a thin gold foil. He fired tiny, positively charged particles at the foil. If the Thomson model were correct, most particles would pass through with some deflection. However, Rutherford observed that while most particles passed straight through, a very small number (about 1 in 10,000) were deflected significantly or even bounced back.
Rutherford concluded that atoms are mostly empty space with a tiny, stable, positively charged nucleus at the center, explaining why most particles passed through. The few particles that were deflected or bounced back must have hit or passed close to this dense, positively charged nucleus. To maintain electrical neutrality, negatively charged electrons must form a shell around this nucleus.
Rutherford's atomic model states that atoms consist of a positively charged nucleus and a negatively charged electron shell, with equal numbers of positive and negative charges to ensure neutrality. The atomic nucleus is extremely small (about 10,000 times smaller) compared to the entire atom and contains most of its mass. This model was a significant advancement, replacing older ideas of atoms as simple spheres or 'plum puddings,' and provided a foundation for future atomic theories.