C1.5 - History of The Atom

Question 1

How has the theory of the atomic structure changed over time?

Answer 1

• 19th century John Dalton described atoms as solid spheres which could not be divided.
• JJ Thomson came up with the “Plum Pudding” model which was evidence for electrons
• Ernest Rutherford conducted alpha particle expiriment : evidence for the nucleus
• Niels Bohr suggested electrons orbit nucleus
• Existence of protons proved by James Chadwick

Question 2

Describe the alpha particle expiriment.

Answer 2

Ernest Rutherford conducted it by firing positivley charged alpha particles at a thin sheet of gold. Many particles went through showing atoms are mainly empty space. However, some particles were deflected suggesting the centre of the atom has a positive charge. Furthermore, some bounced back suggesting the centre contained a large amount of mass (now called the nucleus).

Question 3

What should have happened in the alpha-scattering expiriment according to the plum pudding model?

Answer 3

Alpha particles to pass straight through the sheet or slight deflection because it was thought that the positive charge was more spread out.

Question 4

What is the plum pudding model?

Answer 4

JJ Thompson theorised that the atom is a ball of positive charge with electrons stuck in it.