Rutherford Gold Foil Experiment - Online Tutor, Practice Problems & Exam Prep

Ernest Rutherford's gold foil experiment, also known as the Geiger-Marsden experiment, revealed the atom's nuclear model, challenging Thomson's plum pudding model. By bombarding gold foil with alpha particles, Rutherford discovered a dense, positively charged nucleus containing protons and neutrons, surrounded by a cloud of electrons. This groundbreaking work established that the nucleus holds most of the atom's mass and fundamentally changed atomic theory, leading to a deeper understanding of atomic structure and behavior.

Rutherford Gold Foil Oil Experiment

In 1911, Ernest Rutherford's gold foil experiment led to the discovery of the positively charged nucleus within an atom. Now, he was assisted by fellow chemists Hans Geiger and Ernest Marsden. And because they had such a big role in this experiment, it's sometimes also referred to as the Geiger Marsden experiment. Just remember that this experiment is known by both of these names: the Rutherford gold experiment as well as the Geiger Marsden experiment. The experimental setup is a thin sheet of gold foil. Here we have our gold foil right here, bombarded with alpha particles emitting from a radioactive element.

The alpha particle itself is a radioactive particle consisting of 2 protons and 2 neutrons. If we were to write out its elemental symbol, we would say it has 2 protons, which means its atomic number is 2. Its mass number, the total of neutrons and protons together, would be 4, and we would use the alpha symbol. Here we're not talking about any electrons involved; neutrons are neutral, protons are positive, so the overall charge would be 2+. An element on the periodic table also has an atomic number of 2, and that would be helium. So another way of depicting this alpha particle is 42He+2.

The radioactive element is encased within this lead box with one part of it open which emits the alpha particles. The radioactive element itself is usually iridium, and again it's encased within this lead container. Around this gold foil or gold sheet, we're going to have what's called our detecting screen. This screen right here has a small slit which allows for the passage of the alpha particles to enter. What happens here is that the alpha particles emitted from the iridium would go through the gold foil and hit the back of the detecting screen. However, we also found that some of these positively charged alpha particles would be striking something in the center of the gold foil. This would cause some of these alpha particles to change trajectories; they wouldn't go straight through it. They would hit different parts of the detecting sheet, which surprised our chemists. In some cases, the alpha particle would shoot out towards the gold foil and come right back towards the radioactive source.

From this, Rutherford was able to come up with his three postulates. The postulates were, firstly, that the proton and neutron are located in the nucleus, which lies at the center of the atom. Rutherford was also able to determine that although incredibly small, the nucleus comprised most of the mass of the atom. Finally, Rutherford figured out that surrounding the dense positively charged nucleus is a cloud of electrons. From the gold foil experiment, we were able to come up with these three postulates in the case of Rutherford and his assistants. These are seen as common ideas today, but back then, they were pretty groundbreaking and went against many laws that chemists considered at the time. This kind of turned all that on its head and challenged a lot of the conceptions that chemists had at that time. Through the actions of Rutherford, Geiger, and Marsden, we have a better understanding of the atom.

Rutherford Gold Foil Oil Experiment Example 1

In this example question, it says, the gold foil Rutherford used in his experiment had a thickness of approximately 6.0 times 10 to the minus 3 millimeters. If a single gold atom has a diameter of 2.910-8 cm, how many atoms thick was Rutherford's foil? Alright. So here we need to determine what is our end amount. Here, they want us to determine the amount of atoms, so the number of atoms will be our end amount. Our given amount is just the value that possesses only 1 unit connected to it. Within this question, we have 2 values being given. Here, they're saying that we have 6.0×10-3 mm. And in this other value, it's actually not alone. It's actually a conversion factor. It's telling us one atom has this value. So the conversion factor is 1 atom is 2.910-8cm. Remember, we're going to start with our given amount, which is just a value alone that is not connected to another unit. So we have 6.0×10-3mm. That is our given amount. Remember, we use conversion factors to go from our given amount to our end amount. And realize here that if I can convert these millimeters into centimeters, they can cancel out with these centimeters. And in that way, we can isolate atoms at the end. So that is the approach we're going to take. So our first conversion factor is just going to be converting millimeters to meters. Remember, the coefficient of 1 goes on the side with the metric prefix, meaning 1 milli is 10 to the negative 3. Millimeters cancel out, now I have meters. For conversion factor 2 now, I'm going to go from meters to centimeters. 1 centi is 10 to the negative 2. Now that I have centimeters, I can now bring in my conversion factor from the question itself, which is conversion factor 3. So 2.910-8cm per 1 atom. So here, centimeters cancel out, and I'll have atoms at the end. Make sure you put this in a parenthesis in your calculator; otherwise, you might get the incorrect answer. And remember, we do that every time we have 10 to the power. If you do that correctly, you'll get as your final answer, 2.1104 atoms. So we would have 2.1104 atoms in terms of the other atoms involved in the thickness of Rutherford's foil.

Rutherford Gold Foil Oil Experiment

Now through the use of the Rutherford Gold Foil Experiment, we're able to develop a new model for the atom itself. We coin it the nuclear model. Now before Rutherford's nuclear model, we had Thomson's plum pudding model. Now with the plum pudding model, it was believed that the atom itself had dispersed around it electrons. So these negatively charged electrons dispersed evenly throughout the atom. Now to counterbalance these electrons, we actually had positive charges embedded within the atom. This overall gave the atom a neutral charge. Now if this were true, when Rutherford used his alpha particles, this should have all shot through the atom. However, we saw that some of the alpha particles were being deflected from something near the center of the atom itself. This helped to create the nuclear model. So with the nuclear model and the ejection of alpha particles from our lead container towards the atom, we saw that some of these alpha particles were deflecting back as we fired alpha particles towards them. Now, of course, some of them did go through because they wouldn't interact with the nucleus itself. But just realize, because of the gold foil experiment, Rutherford was able to put to rest this plum pudding model first theorized by Thomson, and give us this more accurate nuclear model.

Rutherford Gold Foil Oil Experiment Example 2

In this example, it says, Rutherford's experiment with alpha particles scattering by gold foil established that electrons are positively charged subatomic particles. Even if we didn't know anything about Rutherford's experiment, we should know that this statement is false. Electrons are not positively charged subatomic particles; they're negatively charged subatomic particles. Besides, it didn't prove this. It just proved that at the center of the atom rested a positively charged portion, and we know that portion is the nucleus.

Next, atoms are composed of protons, neutrons, and electrons. Now, yes, the atom is composed of these subatomic particles. Yes. Electrons do orbit the nucleus. Rutherford knew that the nucleus itself was positive, but he wouldn't have known that there were neutrons embedded in it as well because remember, neutrons possess no charge. There'd be no way of him knowing that they existed within the nucleus as well. So this is not true. Protons are not evenly distributed throughout an atom. Now here, this is true. Protons are not distributed evenly throughout an atom like Thomson's plum pudding model would have suggested. The gold foil experiment proved that at the center of the atom itself is where we have a concentration of those protons. So this would be the most accurate.

Finally, protons are about a thousand times lighter than electrons. This is also true. We know that the subatomic particles, neutrons are the heaviest, followed by protons, and then electrons would be the lightest. Also, if the center were highly dense as we believed, we'd expect the protons to be much heavier than the electrons themselves. So here, only option C would be the correct choice.

Here’s what students ask on this topic:

What was the Rutherford Gold Foil Experiment?

The Rutherford Gold Foil Experiment, also known as the Geiger-Marsden experiment, was conducted in 1911 by Ernest Rutherford with the assistance of Hans Geiger and Ernest Marsden. The experiment involved bombarding a thin sheet of gold foil with alpha particles emitted from a radioactive source. The setup included a detecting screen to observe the deflection of these particles. The results showed that while most alpha particles passed through the foil, some were deflected at large angles, and a few even bounced back. This led to the discovery of a dense, positively charged nucleus at the center of the atom, surrounded by a cloud of electrons, fundamentally changing the atomic model from Thomson's plum pudding model to the nuclear model.

What were the key findings of the Rutherford Gold Foil Experiment?

The key findings of the Rutherford Gold Foil Experiment were groundbreaking. First, it revealed that the atom has a small, dense, positively charged nucleus at its center, which contains protons and neutrons. Second, it showed that most of the atom's mass is concentrated in this nucleus. Third, it demonstrated that the nucleus is surrounded by a cloud of electrons. These findings contradicted the then-accepted Thomson's plum pudding model, which posited that electrons were evenly distributed within a positively charged 'soup.' Instead, Rutherford's experiment established the nuclear model of the atom, which is the basis for our current understanding of atomic structure.

How did the Rutherford Gold Foil Experiment disprove the plum pudding model?

The Rutherford Gold Foil Experiment disproved the plum pudding model by showing that alpha particles were deflected at large angles when they encountered the gold foil. According to the plum pudding model, which suggested that electrons were evenly distributed within a positively charged 'soup,' the alpha particles should have passed through the foil with minimal deflection. However, the experiment revealed that some alpha particles were deflected back, indicating the presence of a dense, positively charged nucleus. This finding was inconsistent with the plum pudding model and led to the development of the nuclear model of the atom, where electrons orbit a central nucleus.

What is the significance of the Rutherford Gold Foil Experiment in atomic theory?

The Rutherford Gold Foil Experiment is highly significant in atomic theory as it fundamentally changed our understanding of atomic structure. Before this experiment, the widely accepted model was Thomson's plum pudding model. Rutherford's findings revealed that the atom consists of a small, dense, positively charged nucleus containing protons and neutrons, with electrons orbiting this nucleus. This nuclear model of the atom explained the deflection of alpha particles observed in the experiment and provided a more accurate representation of atomic structure. It laid the groundwork for future developments in quantum mechanics and the study of atomic behavior, influencing modern chemistry and physics.

Who were the key scientists involved in the Rutherford Gold Foil Experiment?

The key scientists involved in the Rutherford Gold Foil Experiment were Ernest Rutherford, Hans Geiger, and Ernest Marsden. Ernest Rutherford, a New Zealand-born physicist, led the experiment and is credited with the discovery of the atomic nucleus. Hans Geiger, a German physicist, and Ernest Marsden, a British physicist, were Rutherford's assistants and played crucial roles in conducting the experiment. Due to their significant contributions, the experiment is sometimes also referred to as the Geiger-Marsden experiment. Together, their work provided critical insights into the structure of the atom and challenged the existing atomic models of their time.