Scientists have long been curious about the internal structure of an atom – which particles are inside it and how they are arranged – and proposed various atomic models to explain it. This chapter covers Rutherford's and Bohr's models, the neutron, atomic and mass numbers, electronic configuration, valency, isotopes, isobars and isotones, three laws of chemical combination and quantum numbers.
1. Discovery of the Nucleus – Rutherford's Gold Foil Experiment
In 1911, Lord Rutherford, a scientist from New Zealand, bombarded a thin gold foil with very small positively charged particles called alpha (α) particles. He selected gold because he wanted as thin a layer as possible and gold is the most malleable metal.
Observations
- Most of the alpha particles passed straight through the foil.
- Some alpha particles were slightly deflected from their straight path.
- Very few alpha particles completely bounced back.