Question

Who discovered the nucleus? Describe the experiment that led to this discovery.

Short answer

Answer: Ernest Rutherford discovered the nucleus through conducting the gold foil experiment in 1911, which involved observing the behavior of alpha particles as they passed through a thin gold foil. This experiment led to the proposal of a new atomic model, which included a central positive charge called the nucleus.

Step-by-step solution

Scientist who discovered the nucleus

The nucleus was discovered by Ernest Rutherford, a New Zealand-born British physicist, in 1911.

Overview of Rutherford's experiment

The experiment conducted by Ernest Rutherford, which ultimately led to the discovery of the nucleus, is known as the gold foil experiment, or the Rutherford's alpha particle scattering experiment. In this experiment, Rutherford and his assistants attempted to understand the structure of an atom by observing the behavior of alpha particles as they passed through a thin gold foil.

Set up the experiment

Rutherford and his team set up the experiment by placing a radioactive substance (which emitted alpha particles) in a lead box. A tiny hole in the box allowed the alpha particles to exit in a straight line. These alpha particles then moved towards a thin gold foil, which was surrounded by a circular fluorescent screen. The screen would light up when struck by the alpha particles, helping the researchers to trace the particles' trajectory.

Observe the alpha particles

As the alpha particles passed through the gold foil, Rutherford and his team observed their behavior on the fluorescent screen. They expected most of the alpha particles to pass straight through the foil with little or no deflection, based on the previous atomic model (Thomson's plum pudding model), which suggested that the positive charge within an atom was evenly distributed throughout its volume.

Analyze the results

Rutherford and his team were surprised to find that while most alpha particles did indeed pass straight through the gold foil, a small portion of them were deflected at various angles. Some alpha particles even bounced back towards the source, as if they had encountered a strong repulsive force within the gold atoms. This observation was inconsistent with Thomson's plum pudding model and indicated the presence of a concentrated positive charge within the atom.

Propose a new atomic model

Based on the experimental results, Rutherford proposed a new atomic model that included a central positive charge, which he called the nucleus. According to Rutherford's nuclear model, the positive charge (protons) and most of the atom's mass were concentrated in a small central region (the nucleus), while the electrons were dispersed in the surrounding space. This model explained the observed deflection and backscattering of alpha particles as they interacted with the concentrated positive charge of the nucleus. In conclusion, Ernest Rutherford discovered the nucleus and proposed a new atomic model through his groundbreaking gold foil experiment. This experiment challenged the previously accepted understanding of atomic structure and laid the foundation for modern atomic theory.

Key concepts

Rutherford's gold foil experiment

Ernest Rutherford, a trailblazer in physics, devised the gold foil experiment in 1911. This experiment was critical in reshaping our understanding of atomic structure. Rutherford's team sought to explore how alpha particles behaved when directed at a thin sheet of gold.

The ingenious setup involved a radioactive source emitting alpha particles inside a lead box. A small opening in the box allowed these particles to travel in a linear path towards a thin gold foil. Surrounding this foil was a circular fluorescent screen, which lit up upon impact by the alpha particles. This setup enabled the researchers to observe and track the paths and behaviors of the particles as they struck the screen.

The expectation, guided by the then-popular Thomson's plum pudding model, was that particles would pass through without much deflection. However, to the astonishment of Rutherford and his team, not all particles behaved as expected. A few deflected at sharp angles, and some even rebounded entirely.

This surprising observation indicated a flaw in existing atomic models and raised questions about the distribution of positive charge within an atom. The gold foil experiment thus set the stage for a significant shift in atomic theory.

Alpha particle scattering

The scattering of alpha particles revealed vital clues about atomic structure. During Rutherford's experiment, most alpha particles passed through the gold foil, evidencing that atoms are mostly empty space. However, those that deflected signaled something more profound.

In the setup, alpha particles were expected to stream through without much hindrance due to the diffused charge distribution suggested by previous models. But when a fraction of the particles scattered at notable angles, it indicated a different story.

The scattering suggested interactions with a concentrated mass capable of exerting a significant repulsive force, causing deflection. Some particles even bounced back, implying a direct hit on a very dense and positively charged region. This discovery was crucial.

• Most particles passing through: Indicating the sparse nature of atoms.
• Deflected particles: Hinting at a concentrated core within atoms.
• Back-scattering: Revealing the presence of a dense, positively charged nucleus.

These interactions with the gold foil highlighted that conventional models couldn't account for all observed behaviors and that a new paradigm was necessary.

Rutherford atomic model

The anomalies observed in the gold foil experiment led Rutherford to propose a revolutionary atomic model. This model was foundational in shifting scientific perspectives from the prior "plum pudding" approach.

Rutherford's atomic model introduced the concept of a nucleus at the atom's center, housing protons, which are positively charged particles. The nucleus was incredibly compact and contained most of the atom's mass.

Surrounding this dense nucleus were electrons, orbiting in the vast empty space that constitutes most of the atom's volume. This model explained the scattering results succinctly, attributing the deflection to interactions with the nucleus without evenly distributed charge.

• Nucleus: A tiny, dense region with positive charge and majority of mass.
• Electrons: Orbiting the nucleus, occupying the wider, mostly empty space.

This paradigm shift not only countered the plum pudding model but also set the groundwork for further developments in atomic theory, enhancing the understanding of atomic interactions and structures. Through this model, Rutherford cracked open the door to more intricate atomic studies, which have continued to revolutionize physics and chemistry.