Question

The scattering of \(\alpha\) particles by thin metal foils established that (a) the mass of an atom is concentrated in a positively charged nucleus (b) electrons are fundamental particles of all matter (c) all electrons carry the same charge (d) atoms are electrically neutral

Short answer

The correct answer is (a) the mass of an atom is concentrated in a positively charged nucleus.

Step-by-step solution

Identification

Identifying what Rutherford's gold foil experiment actually demonstrated. This experiment involved the scattering of alpha particles. By observing the pattern of scattered particles, Rutherford made important conclusions about the structure of an atom.

Applying Rutherford's findings

Rutherford observed that most of the alpha particles passed straight through the thin foil, suggesting that most of an atom's space is empty. However, a few particles were deflected at large angles or bounced back, which could only be accounted for if there was a centralized mass present in the atom that was positively charged. This led to the conjecture that the mass of an atom is concentrated in a positively charged nucleus. Hence, statement (a) correctly applies Rutherford's findings and his conclusion from the gold foil experiment.

Ruling out incorrect options

Though statements (b), (c), and (d) are facts about atoms and particles, they were not the primary findings from the scattering of alpha particles. These statements are about electron properties and electrical neutrality of atoms, which were not the major conclusions from Rutherford's experiment. Therefore, statements (b), (c), and (d) can be ruled out.

Key concepts

Alpha Particle Scattering

Rutherford's gold foil experiment is a classic study illustrating how alpha particles, which are positively charged helium nuclei, interact with matter. In this experiment, Rutherford directed a beam of alpha particles at a thin sheet of gold foil. Most of the particles passed through the foil without any deflection.
However, a small number were deflected at large angles, and some even bounced back towards the source. This scattering pattern was crucial.
Rutherford's observations were unexpected because, according to the previous atomic model (the "plum pudding model"), such large deflections should not have occurred if the positive charge was spread out evenly within the atom.

• The majority of alpha particles passed through, indicating that atoms are mostly empty space.
• Some particles deflected at large angles, suggesting a concentrated mass within the atom.
• The returning particles showed that this mass was also positively charged.

These insights ruled out the plum pudding model and paved the way for a new atomic theory that places the mass of the atom in a centralized nucleus.

Nuclear Model of the Atom

The results of Rutherford's experiment led to the development of the nuclear model of the atom. According to this model, the atom consists of a small, dense nucleus containing positively charged protons and neutral neutrons. This nucleus holds the majority of the atom's mass.
The understanding was that electrons orbit the nucleus, similar to how planets orbit the sun, but in a less predictable path.
With the mass concentrated in this nucleus, it became clear why most alpha particles passed through or slightly deflected.
Rutherford's nuclear model described an atom quite differently than the earlier models:

• The atom has a tiny, dense nucleus where the mass is concentrated.
• Electrons revolve around this nucleus.
• The nucleus is positively charged due to proton presence.

This model provided a more accurate description of atomic structure, aligning with the observed experimental results of alpha particle scattering.

Atomic Structure Conclusions

Rutherford's gold foil experiment led to multiple significant conclusions about atomic structure. First, it confirmed that the atom is mostly empty space, which was indicated by the large number of alpha particles passing straight through the gold foil.
The experiment also revealed the presence of a small, dense nucleus within each atom, accounting for the few alpha particles that were deflected at large angles.
This nucleus was found to carry a positive charge because only a concentrated positive charge could repel the positively charged alpha particles so dramatically.

• Atoms consist chiefly of empty space with a dense center known as the nucleus.
• The nucleus contains positive charges concentrated in protons.
• Electrons are negatively charged particles that orbit the nucleus.

These conclusions fundamentally changed the understanding of atomic structure, providing a foundation for future atomic models and theories in nuclear physics.