What do you think would happen if a-particles were replaced with negatively. Class 9
What do you think would happen if a-particles were replaced with negatively. Class 9
Question 1.
What do you think would happen if a-particles were replaced with negatively charged particles in Rutherford’s gold foil experiment? (Page 144) Class 9
Answer:
If negatively charged particles were used instead of positively charged alpha particles, the result would be very different. The nucleus of gold atoms is positively charged. A negatively charged particle approaching the nucleus would be attracted towards the nucleus (unlike alpha particles which are repelled).
So instead of bouncing back or being deflected at large angles (which happens due to repulsion between like charges), the negatively charged particles would be pulled inward towards the nucleus. Most of them would curve towards the nucleus rather than pass straight through or bounce back. The scattering pattern would be completely different.
Question 2.
Rutherford found that a few a-particles bounced back sharply. How does this single surprising result completely rule out Thomson’s 'plum pudding model' of the atom? (Page 144) Class 9
Answer:
In Thomson's plum pudding model, the positive charge is spread uniformly throughout the entire volume of the atom like a diffuse sphere. If this were true, the positive charge at any point would be extremely weak and spread out. An alpha particle passing through such an atom would never encounter a concentrated or strong enough repulsive force to bounce it back. Even if slightly deflected, the particle could not be deflected at large angles, and certainly could not bounce straight back.
The fact that a few alpha particles did bounce back sharply clearly means there must be a very small, extremely dense, and very strongly positively charged region inside the atom - the nucleus. Only a concentrated mass of positive charge could repel the fast-moving alpha particles so strongly. This single surprising observation completely rules out the plum pudding model and proves that positive charge cannot be spread out uniformly throughout the atom.