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

In 1911, the Rutherford gold foil experiment revealed the atomic structure, leading to the nuclear model of the atom. Alpha particles, emitted from a radioactive source, were directed at a thin gold foil. While most passed through, some were deflected, indicating a dense, positively charged nucleus containing protons and neutrons, surrounded by a cloud of electrons. This challenged Thomson's plum pudding model, establishing the nucleus as the core of atomic mass and fundamentally altering atomic theory.

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. He was assisted by fellow chemists Hans Geiger and Ernest Marsden. Because they had such a big role in this experiment, it's sometimes also referred to as the Geiger-Marsden experiment. So just remember, this experiment is known by both of these names: the Rutherford gold experiment and the Geiger-Marsden experiment. The experimental setup included a thin sheet of gold foil, which is 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, meaning its atomic number is 2. Its mass number, the number of neutrons and protons together, would be a total of 4, and we'd 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 positive 2. Another way of depicting this alpha particle is as He4/He2+2. The radioactive element is encased within a lead box with one part of it open, which emits the alpha particles. Typically, the radioactive element used is iridium and is encased within this lead container.

Around the gold foil or gold sheet, there is a detecting screen with a small slit that allows for the passage of the alpha particles. When alpha particles are emitted from the iridium, some pass through the gold foil and hit the back of the detecting screen. However, some of these positively charged alpha particles strike something in the center of our gold foil, causing some of them to change trajectories. This was surprising as it was expected that all particles would go straight through; some even came right back towards the radioactive source.

From this, Rutherford was able to formulate three postulates: first, that the proton and neutron are located in the nucleus, which lies at the center of the atom; second, that although incredibly small, the nucleus comprises most of the mass of the atom; and third, that surrounding the dense, positively charged nucleus is a cloud of electrons. These findings from the gold foil experiment were groundbreaking at that time and challenged many of the then-accepted laws and conceptions in chemistry."

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 that the gold foil Rutherford used in his experiment had a thickness of approximately \(6.0 \times 10^{-3}\) millimeters. If a single gold atom has a diameter of \(2.9 \times 10^{-8}\) centimeters, how many atoms thick was Rutherford's foil?

Alright. So here, we need to determine what our end amount is. Here they want us to determine the number of atoms, so the number of atoms will be our end amount. Our given amount is just the value that possesses only one unit connected to it. Within this question, we have two values being given. Here, they're saying that we have \(6.0 \times 10^{-3}\) millimeters. And in this other value, it's actually not alone; it's a conversion factor. It's telling us one atom has this value. So, the conversion factor is 1 atom is \(2.9 \times 10^{-8}\) centimeters. 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 \(6.0 \times 10^{-3}\) millimeters. 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 converting 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 \(10^{-3}\). Millimeters cancel up, now I have meters. For conversion factor 2 now, I'm going to go from meters to centimeters. 1 centi is \(10^{-2}\) Now that I have centimeters, I can now bring in my conversion factor from the question itself, which is conversion factor 3. So \(2.9 \times 10^{-8}\) centimeters per 1 atom. So here, centimeters cancel out, and I'll have atoms at the end. Make sure you put this in parenthesis in your calculator, otherwise you may get the incorrect answer. And remember, we do that every time we have times 10 to the power. If you do that correctly, you'll get as your final answer, \(2.1 \times 10^{4}\) atoms. So we would have \(2.1 \times 10^{4}\) 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. Before Rutherford's nuclear model, we had Thomson's plum pudding model. With the plum pudding model, it was believed that the atom itself had dispersed around it electrons. So these negatively charged electrons were evenly dispersed throughout the atom. To counterbalance these electrons, we actually had positive charges embedded within the atom. This overall gave the atom a neutral charge. If this were true, when Rutherford used his alpha particles, they 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. 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. 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 for him to know 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 Thompson'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 1000 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 and what did it discover?

The Rutherford Gold Foil Experiment, conducted in 1911 by Ernest Rutherford with the help of Hans Geiger and Ernest Marsden, involved bombarding a thin sheet of gold foil with alpha particles emitted from a radioactive source. Most alpha particles passed through the foil, but some were deflected, indicating the presence of a dense, positively charged nucleus at the center of the atom. This experiment led to the discovery of the atomic nucleus, which contains protons and neutrons, and is surrounded by a cloud of electrons. This finding challenged the then-accepted Thomson's plum pudding model and established the nuclear model of the atom.

How did the Rutherford Gold Foil Experiment challenge Thomson's plum pudding model?

Thomson's plum pudding model proposed that atoms were composed of a diffuse cloud of positive charge with negatively charged electrons embedded within it, giving the atom an overall neutral charge. According to this model, alpha particles should have passed through the atom without significant deflection. However, the Rutherford Gold Foil Experiment showed that some alpha particles were deflected at large angles, and some even bounced back, indicating the presence of a dense, positively charged nucleus. This evidence contradicted the plum pudding model and led to the development of the nuclear model of the atom, where the nucleus contains most of the atom's mass and positive charge.

What are alpha particles and how were they used in the Rutherford Gold Foil Experiment?

Alpha particles are positively charged particles consisting of 2 protons and 2 neutrons, making them identical to helium nuclei. In the Rutherford Gold Foil Experiment, alpha particles were emitted from a radioactive source, typically iridium, and directed at a thin sheet of gold foil. The behavior of these alpha particles, whether they passed through the foil or were deflected, provided crucial insights into the atomic structure. The deflection of some alpha particles indicated the presence of a dense, positively charged nucleus within the atom, leading to the development of the nuclear model of the atom.

What were the key postulates derived from the Rutherford Gold Foil Experiment?

From the Rutherford Gold Foil Experiment, three key postulates were derived: 1) The atom contains a small, dense, positively charged nucleus at its center, which houses protons and neutrons. 2) The nucleus comprises most of the atom's mass despite its small size. 3) Surrounding the nucleus is a cloud of electrons, which occupy most of the atom's volume but contribute little to its mass. These postulates fundamentally altered the understanding of atomic structure, replacing the plum pudding model with the nuclear model and laying the groundwork for modern atomic theory.

Why was the Rutherford Gold Foil Experiment considered groundbreaking at the time?

The Rutherford Gold Foil Experiment was considered groundbreaking because it provided direct evidence for the existence of a dense, positively charged nucleus within the atom, fundamentally challenging the prevailing Thomson's plum pudding model. Before this experiment, the atom was thought to be a diffuse cloud of positive charge with embedded electrons. The unexpected deflection of alpha particles demonstrated that the positive charge and most of the atom's mass were concentrated in a small central nucleus, leading to the development of the nuclear model of the atom. This discovery significantly advanced the understanding of atomic structure and paved the way for future research in nuclear physics and chemistry.