History of the atom

Question 1

What did John Dalton describe the atom as?

Answer 1

1. At the start of the 19th century John Dalton described atoms as solid spheres, and said that different spheres made up the different elements.

Question 2

How did JJ Thomson come up with the plum pudding model?

Answer 2

1. In 1897, JJ Thomson concluded from his experiments that atoms werent solid spheres.
2. His measurements of charge and mass showed that an atom must contain even smaller, negatively charged particles called electrons.
3. The new theory was known as the plum pudding model. It showed the atom as a ball of positive charge with electrons embedded into it.

Question 3

Describe Ernest Rutherfords experiment?

Answer 3

1. In 1909 Ernest Rutherford conducted the famous alpha particle scattering experiments. They fired positively charged alpha particles at an extremely thin sheet of gold.
2. From the plum pudding model, they were expecting the particles to pass straight through. However, while most did pass straight through, some were deflected more than expected, and a small number were deflected backwards.
3. He concluded that there was a tiny, positively charged nucleus at the centre, where most of the mass was concentrated. He thought that a “cloud” of negatively charged electrons surrounded this nucleus, so most of the atom was empty space.

Question 4

What model of the atom did Rutherford develop?

Answer 4

1. Nuclear model