Rutherford Gold Foil Experiment: Videos & Practice Problems

In 1911, the groundbreaking gold foil experiment conducted by Ernest Rutherford, along with Hans Geiger and Ernest Marsden, revealed the existence of a positively charged nucleus within the atom. This experiment is often referred to by both names: the Rutherford gold experiment and the Geiger-Marsden experiment. The setup involved bombarding a thin sheet of gold foil with alpha particles emitted from a radioactive source, typically iridium, which was encased in a lead box with an opening to allow the particles to escape.

Alpha particles are composed of 2 protons and 2 neutrons, giving them an atomic number of 2 and a mass number of 4. This can be represented as ^4_2He^{2+}, indicating their positive charge due to the presence of protons. As the alpha particles passed through the gold foil, most traveled straight through, but some were deflected at various angles, and a few even bounced back towards the source. This unexpected behavior led to significant conclusions about atomic structure.

From the observations made during the experiment, Rutherford formulated three key postulates regarding atomic structure: first, that protons and neutrons reside in the nucleus at the center of the atom; second, that the nucleus, although very small, contains most of the atom's mass; and third, that a cloud of electrons surrounds this dense, positively charged nucleus. These insights were revolutionary at the time, challenging existing theories and fundamentally altering the understanding of atomic structure.

Overall, the contributions of Rutherford, Geiger, and Marsden significantly advanced the field of chemistry, providing a clearer picture of the atom and laying the groundwork for future research in atomic theory.

To determine how many gold atoms thick Rutherford's foil was, we start with the thickness of the foil, which is given as \(6.0 \times 10^{-3}\) millimeters. We also know that a single gold atom has a diameter of \(2.9 \times 10^{-8}\) centimeters. The goal is to find the number of atoms that make up the thickness of the foil.

First, we need to convert the thickness from millimeters to centimeters, as the diameter of the atom is given in centimeters. The conversion factor for millimeters to centimeters is that \(1\) millimeter equals \(0.1\) centimeters, or \(1 \text{ mm} = 10^{-2} \text{ cm}\). Thus, we can convert the thickness:

\[6.0 \times 10^{-3} \text{ mm} \times \frac{1 \text{ cm}}{10^{-2} \text{ mm}} = 6.0 \times 10^{-1} \text{ cm}\]

Now, we have the thickness of the foil in centimeters as \(6.0 \times 10^{-1}\) cm. Next, we will use the diameter of a single gold atom to find out how many atoms fit into this thickness. The diameter of one gold atom is \(2.9 \times 10^{-8}\) cm. To find the number of atoms, we divide the thickness of the foil by the diameter of a single atom:

\[\text{Number of atoms} = \frac{6.0 \times 10^{-1} \text{ cm}}{2.9 \times 10^{-8} \text{ cm}} \]

Calculating this gives:

\[\text{Number of atoms} \approx 2.1 \times 10^{7}\]

Thus, Rutherford's foil is approximately \(2.1 \times 10^{7}\) atoms thick. This calculation illustrates the relationship between macroscopic measurements and atomic dimensions, highlighting the incredibly small size of atoms in comparison to everyday objects.

The Rutherford Gold Foil Experiment was pivotal in reshaping our understanding of atomic structure, leading to the development of the nuclear model of the atom. Prior to this experiment, the prevailing theory was Thomson's plum pudding model, which proposed that atoms were composed of a uniform distribution of positive charge with negatively charged electrons embedded throughout, resulting in an overall neutral charge.

Rutherford's experiment involved firing alpha particles at a thin sheet of gold foil. According to the plum pudding model, it was expected that these alpha particles would pass through the foil with minimal deflection. However, the results were surprising: while most alpha particles did pass through, a significant number were deflected at large angles, and some even bounced back. This indicated that the positive charge within the atom was concentrated in a small, dense nucleus, rather than being spread out evenly as previously thought.

This led to the conclusion that the atom consists of a central nucleus, containing most of its mass and positive charge, surrounded by electrons that occupy the surrounding space. The nuclear model thus replaced the plum pudding model, providing a more accurate representation of atomic structure. The experiment not only demonstrated the existence of the nucleus but also laid the groundwork for future developments in atomic theory, including the understanding of atomic behavior and interactions.

Rutherford's gold foil experiment was pivotal in shaping our understanding of atomic structure. It demonstrated that atoms consist of a dense, positively charged nucleus, which contains protons, while electrons orbit this nucleus. Contrary to the misconception that electrons are positively charged, they are actually negatively charged subatomic particles. This experiment did not reveal the presence of neutrons, which are neutral particles found within the nucleus; their existence was unknown at the time.

Atoms are made up of three primary subatomic particles: protons, neutrons, and electrons. Protons, which carry a positive charge, are concentrated in the nucleus, disproving earlier models like Thomson's plum pudding model that suggested a more uniform distribution of charge throughout the atom. Neutrons, being neutral, add to the mass of the nucleus but do not affect its charge. In terms of mass, protons are significantly heavier than electrons, with protons being approximately 1,000 times heavier than electrons. This understanding of mass distribution within the atom is crucial, as it highlights the density of the nucleus compared to the surrounding electron cloud.

In summary, Rutherford's findings established that the nucleus is the core of the atom, containing protons and neutrons, while electrons orbit around it, leading to a more accurate model of atomic structure.