Question

Which of the following conclusions regarding the structure of atom is based on Rutherford's \(\alpha\)-particle scattering experiment? (a) The positive charge is concentrated in a very small volume of the atom. (b) The positive charge is scattered with the electrons throughout the atom. (c) The volume occupied by the nucleus is half of the volume of atom. (d) Most of the space in the atom is occupied by the neutrons.

Short answer

(a) The positive charge is concentrated in a very small volume of the atom.

Step-by-step solution

Understanding the Background of the Experiment

Rutherford's alpha-particle scattering experiment showed that when alpha particles are fired at thin gold foil, most pass straight through, some are deflected at small angles, and a few bounce back at large angles. This observation led to the conclusion that the positive charge must be concentrated in a very small volume within the atom, as only a dense center could repel the positively charged alpha particles.

Evaluating the Given Options

Based on the conclusions drawn from the experiment, let's analyze each option. Option (a) suggests the positive charge is concentrated in a small volume, which aligns with Rutherford's findings. Option (b) is incorrect because the experiment did not conclude that positive charge is scattered with the electrons. Option (c) is not a conclusion of the experiment since the actual volume of the nucleus was not determined to be half the volume of the atom. Option (d) is also incorrect because Rutherford's experiment did not provide information about neutrons; it focused on the nucleus and its positive charge.

Identifying the Correct Conclusion

After evaluating the options against the findings of Rutherford's experiment, one can conclude that the correct statement based on his experiment is that the positive charge is concentrated in a very small volume of the atom, as described in option (a).

Key concepts

Atomic Structure

The exploration of atomic structure has captivated scientists for centuries. At the heart of this exploration was Rutherford's alpha-particle scattering experiment, a pivotal moment in atomic theory. This experiment shattered the plum pudding model, which assumed electrons floated in a diffuse positive charge like plums in a pudding.

Instead, Rutherford's observations suggested an atom featuring a central nucleus surrounded by electrons. Most of the atom's space is empty, allowing alpha particles to pass through without deflection. Nevertheless, the few alpha particles that were deflected at sharp angles hinted at the presence of a small, dense, positively charged nucleus — fundamentally altering our understanding of atomic structure.

The atomic structure essentially consists of a central nucleus, comprising protons and (discovered later) neutrons, and electrons orbiting this nucleus at various energy levels. The number of protons within the nucleus defines the identity of the element (its atomic number), while the broader structure influences everything from chemical behavior to the physical properties of the substance.

The Nuclear Model of Atom

The nuclear model of the atom, proposed by Ernest Rutherford, presents the atom as a miniature solar system. The dense nucleus, analogous to the sun, sits at the center, with electrons orbiting around it like planets. This model emerged from the ashes of the plum pudding model and set the stage for a more detailed and accurate depiction of atomic structure.

Rutherford's experiment suggested that the nucleus is incredibly small relative to the atom's total size, yet it holds most of the atom's mass. This understanding leads us to a tantalizing concept: atoms are actually mostly empty space! If atoms were the size of a football stadium, the nucleus would be about the size of a small marble, and the electrons would be akin to tiny peas whizzing around the stands.

The nuclear model also cleared up misconceptions regarding the atom's stability and explained why atoms did not collapse inward, as the positively charged nucleus exerts an electrostatic force that keeps the negatively charged electrons in their orbits, provided they have enough energy.

Positive Charge Distribution in Atom

Rutherford's alpha-particle scattering experiment was groundbreaking because it provided insight into the distribution of positive charge within the atom. Prior to Rutherford, the predominant thought was that positive charge was diffused throughout the atom. However, the unexpected reflection of some alpha particles demonstrated that this was not the case.

The concentration of positive charge in a central nucleus implies that the positive charge doesn't simply roam the atom's expanse but is firmly held within the nucleus. This discovery was monumental because it distinguished the nucleus as a discrete entity, separate from the cloud of surrounding electrons. The subsequent atomic models, including the quantum mechanical model, built upon this foundation, recognizing the nucleus as a compact core where the entirety of an atom's positive charge and most of its mass is located.

The experiment paved the way for the understanding that the electrons' negative charge is found in the electron cloud, a vast region compared to the nucleus, where electrons spend most of their time. The clear distinction between the nucleus and the electron cloud is crucial for comprehending chemical bonding and reactions, as these are governed by the interactions of an atom's outer electrons.