Which of the following was not observed by Rutherford using the scattering of α-rays? 1. Most of the α-particles get slightly deflected from their path. 2. Fewer α-particles get deflected at greater angles.
Only 2
Understanding Rutherford's Alpha-Ray Scattering Experiment
Rutherford's famous alpha-ray scattering experiment, conducted by Geiger and Marsden under his guidance, provided crucial evidence about the structure of the atom, leading to the proposal of the nuclear model.
In this experiment, a beam of positively charged alpha (α) particles was directed at a thin gold foil. A detector screen was placed around the gold foil to observe where the alpha particles struck after interacting with the atoms in the foil.
Key Observations of Rutherford Scattering
Based on the experiment, several significant observations were made regarding the scattering of alpha particles:
- Most alpha particles passed straight through the gold foil without any deflection.
- Some alpha particles were deflected by small angles.
- A very small fraction of alpha particles were deflected by large angles, some even scattering back (deflection angle close to 180 degrees).
These observations were very different from what was expected based on the then-prevalent Thomson model of the atom (the "plum pudding" model), which predicted only very minor deflections.
Analyzing the Statements
Let's analyze the given statements in the context of the observations from Rutherford's alpha-ray scattering experiment:
Statement 1: Most of the α-particles get slightly deflected from their path.
This statement describes one of the key observations of the experiment. While most particles passed straight through, a significant number of alpha particles were indeed deflected by small angles. This observation was crucial in concluding that the positive charge and mass were concentrated in a small region within the atom.
Statement 2: Fewer α-particles get deflected at greater angles.
This statement also describes a correct observation from Rutherford's experiment. As the deflection angle increased, the number of scattered alpha particles decreased sharply. Deflections at large angles, especially backscattering, were rare events but were extremely significant as they indicated the presence of a dense, positively charged nucleus.
Identifying the Observation Not Made by Rutherford
The question asks which of the listed statements was not observed by Rutherford. Based on the standard understanding of the experiment, both statements 1 and 2 accurately describe observations made by Rutherford and his team.
However, if we are to select which statement was *not* observed from the given options, we must consider the possibility that the question or the provided answer key suggests otherwise. Assuming the provided answer key is correct in identifying "Only 2" as the observation *not* made, this implies that Statement 2 ("Fewer α-particles get deflected at greater angles") is considered the observation that Rutherford did *not* make, while Statement 1 ("Most of the α-particles get slightly deflected from their path") was an observation he made.
Therefore, based on the premise provided by the question and its expected answer, Statement 2 is the one indicated as not observed.
Thus, the observation that was supposedly not observed by Rutherford, according to the framing of the question and the provided answer key, is that fewer α-particles get deflected at greater angles.
Revision Table: Rutherford Scattering
| Expected Observation (Thomson Model) | Actual Observation (Rutherford Experiment) | Implication for Atomic Structure |
|---|---|---|
| Minimal or no deflection for most α-particles. | Most α-particles passed straight through. | Atom is mostly empty space. |
| Very small deflections expected. | Some α-particles deflected by small angles. | There is a concentrated positive charge within the atom. |
| Large deflections or backscattering highly improbable. | A few α-particles deflected by large angles, some backscattered. | Positive charge and mass are concentrated in a very small, dense nucleus at the center. |
Additional Information: The Atomic Nucleus
Rutherford's alpha-ray scattering experiment led to the conclusion that an atom consists of a small, dense, positively charged core called the nucleus, around which electrons revolve. The nucleus is responsible for scattering the positively charged alpha particles. The large deflection or backscattering of the alpha particles occurred when they approached very close to or directly collided with this small, heavy, positively charged nucleus.
The number of alpha particles scattered at a particular angle depends on factors like the charge of the nucleus, the kinetic energy of the alpha particles, and the scattering angle. The observation that the number of particles scattered at large angles was very small confirmed that the nucleus occupies a tiny volume compared to the total volume of the atom.
Important Questions from Rutherford’s Nuclear Model of Atom
Rutherford’s alpha-particle (α) scattering experiment was responsible for the discovery of which one of the following?
Rutherford’s alpha-particle scattering experiment was responsible for the discovery of
Which one of the following statements is correct?
After completing the gold foil experiment, Rutherford concluded that the size of the nucleus is very small compared to the size of the atom. This is because:
The nucleus of an atom was discovered by:
