Question

Predict and test the behaviour of α particles fired at a Rutherford atom model.

(a) Predict the paths taken by α particles that are fired at atoms with a Rutherford atom model structure. Explain why you expect the α particles to take these paths.

(b) If α particles of higher energy than those in (a) are fired at Rutherford atoms, predict how their paths will differ from the lower-energy α particle paths. Explain your reasoning.

(c) Predict how the paths taken by the α particles will differ if they are fired at Rutherford atoms of elements other than gold. What factor do you expect to cause this difference in paths, and why?

(d) Now test your predictions from (a), (b), and (c).

Open the Rutherford Scattering simulation (http://openstaxcollege.org/l/16PhetScatter) and select the “Rutherford Atom” tab. Due to the scale of the simulation, it is best to start with a small nucleus, so select “20” for both protons and neutrons, “min” for energy, show traces, and then start firing α particles. Does this match your prediction from (a)? If not, explain why the actual path would be that shown in the simulation. Pause or reset, set energy to “max,” and start firing α particles. Does this match your prediction from (b)? If not, explain the effect of increased energy on the actual path as shown in the simulation. Pause or reset, select “40” for both protons and neutrons, “min” for energy, show traces, and fire away. Does this match your prediction from (c)? If not, explain why the actual path would be that shown in the simulation. Repeat this with larger numbers of protons and neutrons. What generalization can you make regarding the type of atom and effect on the path of α particles? Be clear and specific.

Short answer

1. Because the Rutherford atom has a tiny, positively charged nucleus, most particles will travel undeflected through an empty space distance from a nucleus. Positive-positive repulsion causes the particles passing close to a nucleus to be diverted from their trajectories. The greater the deflection angle, the more directly the particles are directed toward the nucleus.
2. Higher-energy particles passing close to a nucleus will still be deflected, but the faster they travel, the smaller the expected angle of deflection.
3. If a nucleus is smaller, the positive charge is smaller, and the expected deflections are also smaller, both in terms of how near the particles pass by the nucleus undeflected, and in terms of the angle of deflection. If a nucleus is larger, the positive charge is larger, and the predicted deflections are larger—more particles will be deflected, with larger deflection angles.
4. The particle pathways match the predictions from (a), (b), and (c).

Step-by-step solution

Rutherford atomic model

According to the Rutherford atomic model, positively charged particles and the majority of an atom's mass are contained in an exceedingly small container.He called this part of the atom the “nucleus.” Negatively charged electrons surround an atom's nucleus, according to the Rutherford model.

Plum pudding model

The plum pudding model (sometimes known as Thomson's plum pudding model) is a scientific model of an atom that dates back to the 18th century.The plum pudding model is defined by electrons surrounded by a positive charge volume, similar to negatively charged "plums" embedded in a positively charged "pudding".