Question
Three claims are made about the structure of the atom.
I. Most of the atom is empty space.
II. The positive charge of the atom is concentrated in a small volume.
III. The electrons have discrete energy levels.
Which of these claims can be deduced from the Rutherford-Geiger-Marsden scattering experiment?
A. I and II only
B. I and III only
C. II and III only
D. I, II and III
▶️Answer/Explanation
Ans:A
The Rutherford-Geiger-Marsden scattering experiment, commonly known as the Rutherford gold foil experiment, provided important insights into the structure of the atom. Let’s examine each of the claims in light of this experiment:
I. Most of the atom is empty space:
- This claim can be deduced from the Rutherford-Geiger-Marsden experiment. Rutherford’s experiment showed that alpha particles, which are positively charged, mostly passed through the gold foil with little to no deflection, indicating that the atom is mostly empty space. However, a small fraction of the alpha particles did experience significant deflection, suggesting that there is a concentrated positive charge in a small volume within the atom.
II. The positive charge of the atom is concentrated in a small volume:
- This claim can also be deduced from the Rutherford-Geiger-Marsden experiment. The significant deflection of some alpha particles indicated that the positive charge in the atom is concentrated in a small, dense nucleus at the center of the atom.
III. The electrons have discrete energy levels:
- The Rutherford-Geiger-Marsden experiment did not directly provide information about the discrete energy levels of electrons. This aspect of atomic structure is better explained by later developments in atomic theory, such as Bohr’s model of the atom and quantum mechanics.
Based on the information provided by the Rutherford-Geiger-Marsden experiment, claims I and II can be deduced, but claim III cannot. Therefore, the correct answer is:A. I and II only
Question
The following reaction is proposed for the collision of a proton \(\mathrm{p}\) and a neutron \(\mathrm{n}\).
$
\mathrm{p}+\mathrm{n} \rightarrow \mathrm{p}+\pi^0
$
The neutral pion \(\pi^0\) consists of an up quark and an anti-up quark.
Which conservation law does this equation violate?
A. Baryon number
B. Charge
C. Lepton number
D. Strangeness
▶️Answer/Explanation
Ans:A
In the reaction, the initial state has a baryon number of 2 (one proton and one neutron), and the final state also has a baryon number of 1 one proton . Baryon number is conserved in this reaction.
Question
A nucleus of platinum (Pt) undergoes alpha decay to form an osmium (Os) nucleus as represented by the following reaction.
$
{ }_{78}^{175} \mathrm{Pt} \rightarrow \text { Os + alpha particle }
$
What are the number of protons and the number of neutrons in the osmium nucleus?
▶️Answer/Explanation
Ans:D
In an alpha decay, an alpha particle is a helium-4 nucleus, which consists of 2 protons and 2 neutrons. Therefore, in the reaction:
$$_{78}^{175} \mathrm{Pt} \rightarrow \text { Os + alpha particle }$$
- The osmium (Os) nucleus will have \(78 – 2 = 76\) protons because it loses 2 protons in the decay.
To find the number of neutrons in the osmium nucleus, we need to consider the mass number. The mass number of the platinum (Pt) nucleus is 175, and since it loses an alpha particle (with a mass number of 4), the mass number of the osmium (Os) nucleus will be \(175 – 4 = 171\).
- The number of neutrons in the osmium nucleus is \(171 – 76 = 95\).
So, the osmium (Os) nucleus will have 76 protons and 95 neutrons.
The Geiger–Marsden experiment provides evidence for
A. the existence of discrete atomic energy levels.
B. the existence of the neutron.
C. a dense positively charged nucleus.
D. the stability of some nuclei.
Answer/Explanation
Markscheme
C
The Geiger–Marsden experiments (also called the Rutherford gold foil experiment) were a landmark series of experiments by which scientists learned that every atom has a nucleus where all of its positive charge and most of its mass is concentrated.
In the Geiger–Marsden experiment \(\alpha \)-particles are scattered by gold nuclei. The experimental results provide evidence that
A. \(\alpha \)-particles have discrete amounts of kinetic energy.
B. most of the mass and positive charge of an atom is concentrated in a small volume.
C. the nucleus contains protons and neutrons.
D. gold atoms have a high binding energy per nucleon.
Answer/Explanation
Markscheme
B
The Rutherford Gold Foil Experiment offered the first experimental evidence that led to the discovery of the nucleus of the atom as a small, dense, and positively charged atomic core. Also known as the Geiger-Marsden Experiments.