rutherford gold foil experiment interpretation

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• Rutherford's Gold Foil Experiment

Key Questions

Rutherford's experiment showed that the atom does not contain a uniform distribution of charge.

Explanation:

Thomson's plum pudding model viewed the atom as a massive blob of positive charge dotted with negative charges.

A plum pudding was a Christmas cake studded with raisins ("plums"). So think of the model as a spherical Christmas cake.

When Rutherford shot α particles through gold foil, he found that most of the particles went through. Some scattered in various directions, and a few were even deflected back towards the source.

He argued that the plum pudding model was incorrect. The symmetrical distribution of charge would allow all the α particles to pass through with no deflection.

Rutherford proposed that the atom is mostly empty space. The electrons revolve in circular orbits about a massive positive charge at the centre.

His model explained why most of the α particles passed straight through the foil. The small positive nucleus would deflect the few particles that came close.

The nuclear model replaced the plum pudding model. The atom now consisted of a positive nucleus with negative electrons in circular orbits around it .

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Who did the Gold Foil Experiment?

The gold foil experiment was a pathbreaking work conducted by scientists Hans Geiger and Ernest Marsden under the supervision of Nobel laureate physicist Ernest Rutherford that led to the discovery of the proper structure of an atom . Known as the Geiger-Marsden experiment, it was performed at the Physical Laboratories of the University of Manchester between 1908 and 1913.

The prevalent atomic theory at the time of the research was the plum pudding model that was developed by Lord Kelvin and further improved by J.J. Thomson. According to the theory, an atom was a positively charged sphere with the electrons embedded in it like plums in a Christmas pudding.

With neutrons and protons yet to be discovered, the theory was derived following the classical Newtonian Physics. However, in the absence of experimental proof, this approach lacked proper acceptance by the scientific community.

What is the Gold Foil Experiment?

Description.

The method used by scientists included the following experimental steps and procedure. They bombarded a thin gold foil of thickness approximately 8.6 x 10 -6 cm with a beam of alpha particles in a vacuum. Alpha particles are positively charged particles with a mass of about four times that of a hydrogen atom and are found in radioactive natural substances. They used gold since it is highly malleable, producing sheets that can be only a few atoms thick, thereby ensuring smooth passage of the alpha particles. A circular screen coated with zinc sulfide surrounded the foil. Since the positively charged alpha particles possess mass and move very fast, it was hypothesized that they would penetrate the thin gold foil and land themselves on the screen, producing fluorescence in the part they struck.

Like the plum pudding model, since the positive charge of atoms was evenly distributed and too small as compared to that of the alpha particles, the deflection of the particulate matter was predicted to be less than a small fraction of a degree.

Observation

Though most of the alpha particles behaved as expected, there was a noticeable fraction of particles that got scattered by angles greater than 90 degrees. There were about 1 in every 2000 particles that got scattered by a full 180 degree, i.e., they retraced their path after hitting the gold foil.

Simulation of Rutherford’s Gold Foil Experiment Courtesy: University of Colorado Boulder

The unexpected outcome could have only one explanation – a highly concentrated positive charge at the center of an atom that caused an electrostatic repulsion of the particles strong enough to bounce them back to their source. The particles that got deflected by huge angles passed close to the said concentrated mass. Most of the particles moved undeviated as there was no obstruction to their path, proving that the majority of an atom is empty.

In addition to the above, Rutherford concluded that since the central core could deflect the dense alpha particles, it shows that almost the entire mass of the atom is concentrated there. Rutherford named it the “nucleus” after experimenting with various gases. He also used materials other than gold for the foil, though the gold foil version gained the most popularity.

He further went on to reject the plum pudding model and developed a new atomic structure called the planetary model. In this model, a vastly empty atom holds a tiny nucleus at the center surrounded by a cloud of electrons. As a result of his gold foil experiment, Rutherford’s atomic theory holds good even today.

Rutherford’s Atomic Model

Rutherford’s Gold Foil Experiment Animation

• Rutherford demonstrated his experiment on bombarding thin gold foil with alpha particles contributed immensely to the atomic theory by proposing his nuclear atomic model.
• The nuclear model of the atom consists of a small and dense positively charged interior surrounded by a cloud of electrons.
• The significance and purpose of the gold foil experiment are still prevalent today. The discovery of the nucleus paved the way for further research, unraveling a list of unknown fundamental particles.
• Chemed.chem.purdue.edu
• Chem.libretexts.org
• Large.stanford.edu
• Radioa ctivity.eu.com

Article was last reviewed on Friday, February 3, 2023

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5 responses to “Gold Foil Experiment”

Super very much helpful to me,clear explanation about every act done by our Rutherford that is under different sub headings ,which is very much clear to ,to study .very much thanks to the science facts.com.thank u so much.

Good explanation,very helpful ,thank u ,so much

very clear and helpful, perfect for my science project!

Thank you for sharing the interactive program on the effects of the type of atom on the experiment! Looking forward to sharing this with my ninth graders!

Rutherford spearheaded with a team of scientist in his experiment of gold foil to capture the particles of the year 1911. It’s the beginning of explaining particles that float and are compacted . Rutherford discovered this atom through countless experiments which was the revolutionary discovery of the atomic nuclear . Rutherford name the atom as a positive charge and the the center is the nucleus.

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Experimental Evidence for the Structure of the Atom

George sivulka march 23, 2017, submitted as coursework for ph241 , stanford university, winter 2017, introduction.

The Rutherford Gold Foil Experiment offered the first experimental evidence that led to the discovery of the nucleus of the atom as a small, dense, and positively charged atomic core. Also known as the Geiger-Marsden Experiments, the discovery actually involved a series of experiments performed by Hans Geiger and Ernest Marsden under Ernest Rutherford. With Geiger and Marsden's experimental evidence, Rutherford deduced a model of the atom, discovering the atomic nucleus. His "Rutherford Model", outlining a tiny positively charged atomic center surrounded by orbiting electrons, was a pivotal scientific discovery revealing the structure of the atoms that comprise all the matter in the universe.

The experimental evidence behind the discovery involved the scattering of a particle beam after passing through a thin gold foil obstruction. The particles used for the experiment - alpha particles - are positive, dense, and can be emitted by a radioactive source. Ernest Rutherford discovered the alpha particle as a positive radioactive emission in 1899, and deduced its charge and mass properties in 1913 by analyzing the charge it induced in the air around it. [1] As these alpha particles have a significant positive charge, any significant potential interference would have to be caused by a large concentration of electrostatic force somewhere in the structure of the atom. [2]

Previous Model of the Atom

The scattering of an alpha particle beam should have been impossible according to the accepted model of the atom at the time. This model, outlined by Lord Kelvin and expanded upon by J. J. Thompson following his discovery of the electron, held that atoms were comprised of a sphere of positive electric charge dotted by the presence of negatively charged electrons. [3] Describing an atomic model similar to "plum pudding," it was assumed that electrons were distributed throughout this positive charge field, like plums distributed in the dessert. However, this plum pudding model lacked the presence of any significant concentration of electromagnetic force that could tangibly affect any alpha particles passing through atoms. As such, alpha particles should show no signs of scattering when passing through thin matter. [4] (see Fig. 2)

The Geiger Marsden Experiments

Testing this accepted theory, Hans Geiger and Ernest Marsden discovered that atoms indeed scattered alpha particles, a experimental result completely contrary to Thompson's model of the atom. In 1908, the first paper of the series of experiments was published, outlining the apparatus used to determine this scattering and the scattering results at small angles. Geiger constructed a two meter long glass tube, capped off on one end by radium source of alpha particles and on the other end by a phosphorescent screen that emitted light when hit by a particle. (see Fig. 3) Alpha particles traveled down the length of the tube, through a slit in the middle and hit the screen detector, producing scintillations of light that marked their point of incidence. Geiger noted that "in a good vacuum, hardly and scintillations were observed outside of the geometric image of the slit, "while when the slit was covered by gold leaf, the area of the observed scintillations was much broader and "the difference in distribution could be noted with the naked eye." [5]

On Rutherford's request, Geiger and Marsden continued to test for scattering at larger angles and under different experimental parameters, collecting the data that enabled Rutherford to further his own conclusions about the nature of the nucleus. By 1909, Geiger and Marsden showed the reflection of alpha particles at angles greater than 90 degrees by angling the alpha particle source towards a foil sheet reflector that then would theoretically reflect incident particles at the detection screen. Separating the particle source and the detector screen by a lead barrier to reduce stray emission, they noted that 1 in every 8000 alpha particles indeed reflected at the obtuse angles required by the reflection of metal sheet and onto the screen on the other side. [6] Moreover, in 1910, Geiger improved the design of his first vacuum tube experiment, making it easier to measure deflection distance, vary foil types and thicknesses, and adjust the alpha particle stream' velocity with mica and aluminum obstructions. Here he discovered that both thicker foil and foils made of elements of increased atomic weight resulted in an increased most probable scattering angle. Additionally, he confirmed that the probability for an angle of reflection greater than 90 degrees was "vanishingly small" and noted that increased particle velocity decreased the most probably scattering angle. [7]

Rutherford's Atom

Backed by this experimental evidence, Rutherford outlined his model of the atom's structure, reasoning that as atoms clearly scattered incident alpha particles, the structure contained a much larger electrostatic force than earlier anticipated; as large angle scattering was a rare occurrence, the electrostatic charge source was only contained within a fraction of the total volume of the atom. As he concludes this reasoning with the "simplest explanation" in his 1911 paper, the "atom contains a central charge distributed through a very small volume" and "the large single deflexions are due to the central charge as a whole." In fact, he mathematically modeled the scattering patterns predicted by this model with this small central "nucleus" to be a point charge. Geiger and Marsden later experimentally verified each of the relationships predicted in Rutherford's mathematical model with techniques and scattering apparatuses that improved upon their prior work, confirming Rutherford's atomic structure. [4, 8, 9] (see Fig. 1)

With the experimentally analyzed nature of deflection of alpha rays by thin gold foil, the truth outlining the structure of the atom falls into place. Though later slightly corrected by Quantum Mechanics effects, the understanding of the structure of the the atom today almost entirely follows form Rutherford's conclusions on the Geiger and Marsden experiments. This landmark discovery fundamentally furthered all fields of science, forever changing mankind's understanding of the world around us.

© George Sivulka. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.

[1] E. Rutherford, "Uranium Radiation and the Electrical Conduction Produced By It," Philos. Mag. 47 , 109 (1899).

[2] E. Rutherford, "The Structure of the Atom," Philos. Mag. 27 , 488 (1914).

[3] J. J. Thomson, "On the Structure of the Atom: an Investigation of the Stability and Periods of Oscillation of a Number of Corpuscles Arranged at Equal Intervals Around the Circumference of a Circle; with Application of the Results to the Theory of Atomic Structure," Philos. Mag. 7 , 237 (1904).

[4] E. Rutherford, "The Scattering of α and β Particles by Matter and the Structure of the Atom," Philos. Mag. 21 , 669 (1911).

[5] H. Geiger, "On the Scattering of the α Particles by Matter," Proc. R. Soc. A 81 , 174 (1908).

[6] H. Geiger and E. Marsden, "On a Diffuse Reflection of the α-Particles," Proc. R. Soc. A 82 , 495 (1909).

[7] H. Geiger, "The Scattering of the α Particles by Matter," Proc. R. Soc. A 83 , 492 (1910).

[8] E. Rutherford, "The Origin of α and β Rays From Radioactive Substances," Philos. Mag. 24 , 453 (1912).

[9] H. Geiger and E. Marsden, "The Laws of Deflexion of α Particles Through Large Angles," Philos. Mag. 25 , 604 (1913).

Discovering the Nucleus: Rutherford’s Gold Foil Experiment

History of Chemistry: Rutherford Gold Foil Experiment

In this article, you will learn the history behind the Rutherford Gold Foil Experiment and the events that led to the discovery of the atomic nucleus. If you enjoy this article, check out our other history of chemistry articles linked below!

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Who was Ernest Rutherford?

Ernest Rutherford is known as the father of nuclear physics. Born in Brightwater, New Zealand on August 30th, 1871, Rutherford was the fourth of twelve children. His father was a farmer and his mother a school teacher. From a very early age, Rutherford understood the importance of hard work and the power of education. In school, he excelled greatly and at the age of fifteen won an academic scholarship to study at Nelson Collegiate School. Then, at the age of 19, he won another academic scholarship to study at Canterbury College in Christchurch. A few years later he won another scholarship, the exhibition science scholarship, and he left New Zealand to study at Trinity College, Cambridge in England. While there, he conducted research at the Cavendish Laboratory under his advisor J.J. Thomson .

During his time at Cavendish Lab, Rutherford faced adversity from his peers. Because he was from New Zealand, he was often ostracized by fellow students. In the end, he used this as motivation to succeed. Which he did as he made a multitude of great discoveries through his research in gases and radioactivity. These included the discovery of different types of radiation, radiometric dating, and the nucleus of an atom.

The Rutherford Gold Foil Experiment

The experiment.

While working as a chair at the University of Manchester, Rutherford conducted the gold-foil experiment alongside Hans Geiger and Ernest Marsden. In this experiment, they shot alpha particles –which Rutherford had discovered years prior– directly at a piece of thin gold foil . As the alpha particles passed through, they would hit the phosphorescent screen encasing the foil. When the particles came into contact with the screen, there would be a flash.

Observations

Going into the experiment, Rutherford had formed preconceptions for the experiment based on J.J. Thomson’s plum pudding model . He predicted the alpha particles would shoot through the foil with ease. Some of the particles did manage to pass directly through the foil, but some veered from the path either bouncing back or deflecting. Rutherford found this to be an exciting observation and compared it to shooting a bullet at a piece of tissue and having it bounce back.

From this observation, two deductions were made. Firstly, he concluded most of the atom is composed of empty space. Secondly, he concluded there must be something small, dense, and positive inside the atom to repel the positively charged alpha particles. This became the nucleus, which in Latin means the seed inside of a fruit.

The Nuclear Model

The gold-foil experiment disproved J.J. Thomsons plum pudding model, which hypothesized the atom was positively charged spaced with electrons embedded inside. Therefore, giving way to the nuclear model. In this model, Rutherford theorized the atomic structure was similar to that of the solar system. Where the nucleus was in this middle and surrounded by empty space with orbiting electrons.

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Rutherford ’s nuclear model

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Rutherford overturned Thomson’s model in 1911 with his famous gold-foil experiment, in which he demonstrated that the atom has a tiny, massive nucleus. Five years earlier Rutherford had noticed that alpha particles beamed through a hole onto a photographic plate would make a sharp-edged picture, while alpha particles beamed through a sheet of mica only 20 micrometres (or about 0.002 cm) thick would make an impression with blurry edges. For some particles the blurring corresponded to a two-degree deflection. Remembering those results, Rutherford had his postdoctoral fellow, Hans Geiger , and an undergraduate student, Ernest Marsden, refine the experiment. The young physicists beamed alpha particles through gold foil and detected them as flashes of light or scintillations on a screen. The gold foil was only 0.00004 cm thick. Most of the alpha particles went straight through the foil, but some were deflected by the foil and hit a spot on a screen placed off to one side. Geiger and Marsden found that about one in 20,000 alpha particles had been deflected 45° or more. Rutherford asked why so many alpha particles passed through the gold foil while a few were deflected so greatly. “It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper, and it came back to hit you,” Rutherford said later.

On consideration, I realized that this scattering backwards must be the result of a single collision, and when I made calculations I saw that it was impossible to get anything of that order of magnitude unless you took a system in which the greater part of the mass of the atom was concentrated in a minute nucleus. It was then that I had the idea of an atom with a minute massive centre carrying a charge .

Many physicists distrusted the Rutherford atomic model because it was difficult to reconcile with the chemical behaviour of atoms. The model suggested that the charge on the nucleus was the most important characteristic of the atom, determining its structure. On the other hand, Mendeleyev’s periodic table of the elements had been organized according to the atomic masses of the elements, implying that the mass was responsible for the structure and chemical behaviour of atoms.

Moseley ’s X-ray studies

Henry Gwyn Jeffreys Moseley , a young English physicist killed in World War I , confirmed that the positive charge on the nucleus revealed more about the fundamental structure of the atom than Mendeleyev’s atomic mass . Moseley studied the spectral lines emitted by heavy elements in the X-ray region of the electromagnetic spectrum . He built on the work done by several other British physicists— Charles Glover Barkla , who had studied X-rays produced by the impact of electrons on metal plates, and William Bragg and his son Lawrence , who had developed a precise method of using crystals to reflect X-rays and measure their wavelength by diffraction . Moseley applied their method systematically to measure the spectra of X-rays produced by many elements.

Moseley found that each element radiates X-rays of a different and characteristic wavelength. The wavelength and frequency vary in a regular pattern according to the charge on the nucleus. He called this charge the atomic number . In his first experiments, conducted in 1913, Moseley used what was called the K series of X-rays to study the elements up to zinc . The following year he extended this work using another series of X-rays, the L series. Moseley was conducting his research at the same time that Danish theoretical physicist Niels Bohr was developing his quantum shell model of the atom. The two conferred and shared data as their work progressed, and Moseley framed his equation in terms of Bohr’s theory by identifying the K series of X-rays with the most-bound shell in Bohr’s theory, the N = 1 shell, and identifying the L series of X-rays with the next shell, N = 2.

Moseley presented formulas for the X-ray frequencies that were closely related to Bohr’s formulas for the spectral lines in a hydrogen atom. Moseley showed that the frequency of a line in the X-ray spectrum is proportional to the square of the charge on the nucleus. The constant of proportionality depends on whether the X-ray is in the K or L series. This is the same relationship that Bohr used in his formula applied to the Lyman and Balmer series of spectral lines. The regularity of the differences in X-ray frequencies allowed Moseley to order the elements by atomic number from aluminum to gold . He observed that, in some cases, the order by atomic weights was incorrect. For example, cobalt has a larger atomic mass than nickel , but Moseley found that it has atomic number 27 while nickel has 28. When Mendeleyev constructed the periodic table, he based his system on the atomic masses of the elements and had to put cobalt and nickel out of order to make the chemical properties fit better. In a few places where Moseley found more than one integer between elements, he predicted correctly that a new element would be discovered. Because there is just one element for each atomic number, scientists could be confident for the first time of the completeness of the periodic table; no unexpected new elements would be discovered.

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About Rutherford's Gold Foil Experiment

Five Types of Atomic Models

Ernest Rutherford, originally from New Zealand, is credited as being the father of nuclear physics for his discoveries in atomic structure, even though Hantaro Nagaoka, a physicist from the Imperial University of Tokyo, first proposed the theory of the nucleus as it is known today. Rutherford's "gold foil experiment" led to the discovery that most of an atom's mass is located in a dense region now called the nucleus. Prior to the groundbreaking gold foil experiment, Rutherford was granted the Nobel Prize for other key contributions in the field of chemistry.

The popular theory of atomic structure at the time of Rutherford's experiment was the "plum pudding model." This model was developed in 1904 by J.J. Thompson, the scientist who discovered the electron. This theory held that the negatively charged electrons in an atom were floating in a sea of positive charge--the electrons being akin to plums in a bowl of pudding. Although Dr. Nagaoka had published his competing theory that electrons orbit a positive nucleus, akin to the way the planet Saturn is orbited by its rings, in 1904, the plum pudding model was the prevailing theory on the structure of the atom until it was disproved by Ernest Rutherford in 1911.

The gold foil experiment was conducted under the supervision of Rutherford at the University of Manchester in 1909 by scientist Hans Geiger (whose work eventually led to the development of the Geiger counter) and undergraduate student Ernest Marsden. Rutherford, chair of the Manchester physics department at the time of the experiment, is given primary credit for the experiment, as the theories that resulted are primarily his work. Rutherford's gold foil experiment is also sometimes referred to as the Geiger-Marsden experiment.

The gold foil experiment consisted of a series of tests in which a positively charged helium particle was shot at a very thin layer of gold foil. The expected result was that the positive particles would be moved just a few degrees from their path as they passed through the sea of positive charge proposed in the plum pudding model. The result, however, was that the positive particles were repelled off of the gold foil by nearly 180 degrees in a very small region of the atom, while most of the remaining particles were not deflected at all but rather passed right through the atom.

Significance

The data generated from the gold foil experiment demonstrated that the plum pudding model of the atom was incorrect. The way in which the positive particles bounced off the thin foil indicated that the majority of the mass of an atom was concentrated in one small region. Because the majority of the positive particles continued on their original path unmoved, Rutherford correctly deducted that most of the remainder of the atom was empty space. Rutherford termed his discovery "the central charge," a region later named the nucleus.

Rutherford's discovery of the nucleus and proposed atomic structure was later refined by physicist Niels Bohr in 1913. Bohr's model of the atom, also referred to as the Rutherford Bohr model, is the basic atomic model used today. Rutherford's description of the atom set the foundation for all future atomic models and the development of nuclear physics.

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Analogy Experiment—Projectile Pennies with Rutherford

Atomic theory is a common topic throughout any introductory chemistry course. Regardless of the depth given to the various models and the evidence that led to their creation, it’s likely that Rutherford’s gold foil experiment gets at least some attention in your course.

Editor’s Note: The activity described here has been revised and updated. Some of the changes have been made with the help of comments from readers. If you are logged into your ChemEd X account, you can see those comments at the conclusion of this post. You will find the updated activity HERE .

For me, this topic had always been a bit more lecture-based. Even though I thoroughly enjoyed talking about the history and development of the atom, I didn’t like the feeling of being heavily reliant upon lecture. Additionally, I didn’t like the fact that I wasn’t providing students with an opportunity to generate their own evidence to support the concepts and models that I wanted them to develop. In this post, I propose a simple activity that gives students an opportunity to replicate Rutherford’s experiment through an analogy experiment that may allow for easier conceptualization of the experiment itself and provide additional support for model development.

Before I mention anything to my students about Rutherford’s experiment, I introduce them to an analogy experiment called Projectile Pennies . Though students don’t yet know what exactly this is an analogy to, they will shortly. It is not imperative that they understand the analogy yet anyway. The goal of the experiment is presented to them as follows:

Indirectly calculate the diameter of an unknown object by recording the number of times it is hit with objects of a known diameter.

The key idea here is to emphasize the fact that they will be determining the diameter of something indirectly . All students understand what they would do if I asked them to determine the diameter of a circular object placed in front of them—simply measure it. But what if they were not able to see the object? Obviously this complicates things a bit. This provides a nice opportunity to discuss how often (especially in chemistry) we rely on indirect evidence to help us inferences about the primary claim that is being made.

The experimental setup (figure 1) and the materials needed are simple. Each group receives two meter sticks, 20 pennies, a whiteboard, and an object with a circular bottom. Typically, I give the groups full water bottles to ensure they have enough mass, but you can use different items with a variety of sizes (film canisters, water filled beakers...). 

Figure 1: Side view of experimental setup (left). Top view of experimental setup (right).

One person in the group is designated as the “penny shooter.” While the other members of the group are getting set up, the penny shooter is told to wait out in the hall to avoid knowing the location of the unknown object. Ideally, we want the penny shooter to be unaware of the location of the object to limit the possibility of intentionally shooting pennies directly at the object. In this past, I have tried to decrease this bias even more by blindfolding the penny shooters and allowing them to wear headphones with music playing on full volume. Needless to say, students fight over who gets to be the penny shooter.

The other member(s) of the group have a few simple tasks before and during the experiment.

Getting Set Up

As seen in figure 1 above, students will establish the path by laying down two parallel meter sticks between 70 – 90 cm apart. Place the whiteboard on top of the meter sticks so it is just barely above the ground and can easily lean against a wall, desk, or lab table. Though the figure above suggests leaning it against a wall, it is easier for the group if the whiteboard can lean against something that does not allow pennies to come back unless they hit the unknown object. Once the whiteboard is secure, place the object somewhere behind the whiteboard. Do not place the object directly next to the meter sticks. Before they tell the penny shooter to come in, ensure that a penny can slide under the whiteboard and that the object cannot be seen from the shooter’s perspective.

During the Experiment

The penny shooter will essentially slide the penny toward the whiteboard (the penny should not leave the floor at any point). Once the penny shooter is ready to begin firing pennies, the other group members have a few simple tasks:

• Record the number of times the object is hit.
• Ensure a clear path for the pennies (i.e. if a penny hits and then comes back, remove it from the path).
• Once a round is over, collect the pennies and hand them back to the penny shooter for the next round.

shooting.png

Figure 2: Experimental Setup—Photo taken in my classroom

Typically, I tell each group that they need to fire at least 100 pennies (5 rounds of 20). If we have enough time, I may ask for more but 100 is usually sufficient. Once they have reached the appropriate amount of pennies fired, they record their data and any measurements made in the following table:

Table 1: Organizing data from the experiment

Once they have all the necessary data, I provide them with the equation below, which will allow them to calculate the experimental diameter of their unknown object.

equation.jpg

Figure 3: Equation used to calculate experimental diameter of unknown object

Personally, I decide to give them the equation above simply to save time. However, I can imagine some teachers possibly adding a layer of depth to the investigation by having students derive the equation themselves. Once students have calculated the experimental diameter of the unknown object, they are asked to compare it to the known diameter. Though results will vary, several groups often get within 1 – 1.5 cm of the known diameter—pretty cool! From this experience, students gain insight as to how it is possible to determine the size of an object that cannot be seen.

example_data.jpg

Figure 4: Example data and calculation of diameter

Lastly, I provide four extension questions for each group to answer. Each question is meant to get students thinking about some of the inferences that will soon be made once we start talking about Rutherford’s experiment.

• If you were the one firing the pennies while doing the same experiment and you noticed that some of your pennies actually bounced back toward you, how would you interpret this observation?
• What would this suggest about the mass of the unknown object relative to the penny?
• If you knew that your penny had a positive charge and you witnessed the same effect, what could you conclude about the charge of the unknown object?
• Why did the majority of your pennies not hit the unknown object?

Once we eventually get to discussing Rutherford’s experiment, it is fun to see students make the connections between his experiment and our analogy. I will often hear things like, “Oh, so the alpha particles were just like our pennies!” and other statements describing the similarities between the nucleus and unknown object. Even the realization as to why the majority of pennies did not make contact with the unknown object being similar to the majority of alpha particles going straight through the gold foil is a cool one to hear. I believe having this experience prior to discussing Rutherford’s experiment provides a strong foundation for our students to more easily connect the rather conceptual findings from Rutherford’s experiment. I feel it is better than simply discussing the details of Rutherford’s experiment head on and assuming everyone will just “get it.” When teaching such abstract concepts in chemistry, the more connections we can allow our students to make with previous experience, the easier they will be able to assimilate such experiences with the appropriate concept.

atomic theory, Rutherford, golf foil experiment, alpha particles, nucleus, electrons

About 30 minutes before the discussion.

two meter sticks, 20 pennies, a whiteboard, and an object with a circular bottom (water bottle, soup can, etc).

Have students complete the procedure below and answer the questions before discussing the theory that Rutherford came up with based upon the results of his gold foil experiment.

When logged on to your ChemEd X account you will find the procedure in the Student Document  included in the Supporting Information below.

Gather the materials and provide the goal of the experiment to students.

I do not remember where I heard about this activity initially, but I have been using some form of it since very early in my career. I have seen a variety of versions online. 

All comments must abide by the ChemEd X Comment Policy , are subject to review, and may be edited. Please allow one business day for your comment to be posted, if it is accepted.

Comments 12, results were quite poor..

I did this activity with 2 classes and the outcome was quite poor. Only 1 in 12 groups got data that was near the expected value.  When the results were so bad for my first class, I thought it was because once the penny slider knew approximately where the object was he/she just kept sliding them to the same place.  For that reason I had the object moved after each 20 penny trial and found the data to be just slightly improved. The only option I can think of is to try is to have the object moved after *each* penny is sent through.  (I did check the students' math work and it was correct.)

Any other ideas?

If you still have access to any of their original numbers, see what happens to the results when you subtract the actual radius of the penny instead of subtracting (2 x Diameter) -- see equation below. This was the equation I used to use and it's also the one taken directly from the Modeling Instruction curriculum but I switched it up last year so it's totally possible that my reasoning for changing the equation was wrong.  Please let me know what you find!  Hope that helps.

Re: Results were quite poor

I don't think that was the problem because all of their numbers were too high, not too low.

What is the total number of

What is the total number of pennies they shot?  In your original comment, you had mentioned the phrase "20 penny trial" and I'm just wondering if that meant they only shot 20 pennies total or something else.  

Re: results were poor

They shot 5 sets of 20 pennies each.

I used soup cans as the object.

Artificial inflation

If the pennies are not shot somewhat evenly over the whole area and are focused too closely around the target you will get a larger diameter. Maybe consider making sure placement is random and having the can move locations between sets to help with the randomness. My guess is there will be some bias to target the center subconsciously.

I've worked with the physics teachers on this and we can't figure out the -2d.  To us the equation should be:

D = H * (W-2r)/T

r is the radius of the penny.

Please, someone either explain the "-2d" or agree with our equation above!

After looking at your proposed equation, I replicated the analogy experiment again and got a calculated diameter that was within 3% of the actual diameter of the "unknown object"! In other words...I definitely agree with the new equation. After giving it a bit of thought, it made a lot more sense. I plan to update the blog post to include this new equation. Thank you for finding a more accurate way to calculate this so it can provide a better experience for both students and teachers!  

I would think that once they

I would think that once they hit the object one time...they would tend to shoot it in the same vicinity after that because they know where it is.

blindfold and headphones

Not sure if I mentioned this in the original post but this is why I tend to tell the shooters to wear a blindfold and headphones w/ music on.  Blindfolds are easy since it could just be some item of clothing and these days at least one of the students will have headphones to use.  This has been the best way I've found to improve the randomness in their shooting.

Yes, I experienced this as well. I noticed immediately that once they hit the cup, they aimed for the cup, giving a disproportionate number of hits, resulting in a higher diameter. Even when I warned the next class to find a way to make it random, they had a hard time--it seems human nature to aim for the cup once you hit it!   

One thing I noted students doing that led to a better result was putting 10 pennies down at a time and sliding them all with one hand. Then they could not be aimed at the cup!   

Another solution was to line the pennies up in a row across the front of the board from left to right and then quickly slide one after the other without stopping. That way the entire space was covered and the pennies hitting the cup were proportionate to the space it occupied, which of course was really the goal.   

I really like the mathematical relationship here. In an honors class I would have had them propose the mathematical relationship themselves. As it was instead I gave them the formula and ask them what it was doing. They quickly figured out that it was simply the percentage of times the pennies hit the cup x the total distance under the board. When I asked them about the subtraction of 2x the diameter of the penny, I quickly had students who were able to propose an answer. I was very impressed with both their ability and willingness to figure this out as well as the beauty of the activity that allowed it. It allowed us to brainstorm ideas that might make it work!

updated activity

Thanks to the help of readers, Ben has revised and updated this activity. Please see the updated post . I am closing the comments on this version. The new version is open for comments. Thank you!

Deanna Cullen

ChemEd X High School Editor

• Structure of Atom
• Rutherford Atomic Model And Its Drawbacks

Drawbacks of Rutherford Atomic Model

Rutherford atomic model was the first step in the evolution of the modern atomic model. Ernest Rutherford was a keen scientist who worked to understand the distribution of electrons in an atom. He performed an experiment using alpha particles and gold foil and made the following observations:

• Most of the alpha particles passed straight through the gold foil.
• There was a deflection of the alpha particles by a small angle.
• Very small amount of alpha particles rebounded.

Table of Content

Rutherford atomic model, recommended videos.

• Frequently Asked Questions – FAQs

From his experiment, he came to the following conclusions:

• Most of the space in an atom is empty.
• The space occupied by the positive charges is very small.
• The positive charges and mass of the atom were concentrated in a very small volume within an atom.

From these conclusions, he calculated that the radius of the nucleus is around 10 5 times less than that of the atom.

Rutherford developed a nuclear model of the atom on the basis of his experiment and observations. The Rutherford atomic model has the following features:

• The centre of an atom is called the nucleus. It is positively charged and almost all mass of the atom resides in it.
• Electrons spin around the nucleus in a circular path.
• Comparatively, the size of the nucleus is smaller than the size of the atom.

As before, the Rutherford atomic model was also challenged and questioned by many. Rutherford atomic model failed to explain about the stability of electrons in a circular path.

As per Rutherford’s model, electrons revolve around the nucleus in a circular path. But particles that are in motion on a circular path would undergo acceleration, and acceleration causes radiation of energy by charged particles. Eventually, electrons should lose energy and fall into the nucleus. And this points to the instability of the atom. But this is not possible because atoms are stable. Hence, Rutherford failed to give an explanation on account of this.

To learn more about the Rutherford atomic model with video lessons, download BYJU’S – The Learning App.

Frequently Asked Questions On Drawbacks of Rutherford Atomic Model

What is the rutherford atomic model.

Rutherford atomic model is a nuclear model of the atom based on his experiment and observations. He worked to understand the distribution of electrons in an atom. He performed an experiment using alpha particles and gold foil.

What are the drawbacks of the rutherford atomic model?

Rutherford’s atomic model failed to explain the stability of electrons in a circular path. He stated that electrons revolve around the nucleus in a circular path, but particles in motion would undergo acceleration and cause energy radiation. Eventually, electrons should lose energy and fall into the nucleus. But it never happens.

What were the observations of the rutherford atomic model?

Rutherford observed that most of the alpha particles passed straight through the gold foil, while some of them were deflected by a small angle, and a very few rebounded.

What was the conclusion of the rutherford atomic model?

Rutherford concluded that most of the space in an atom is empty, a positively charged dense particle is present inside the atom that occupies a little space and most of the mass of an atom is concentrated over there.

What are the features of the rutherford atomic model?

Rutherford’s model states that the centre of an atom is the nucleus which is positively charged, occupying most of the atom’s mass. He also explained that electrons spin around the nucleus in a circular path.

Put your understanding of this concept to test by answering a few MCQs. Click ‘Start Quiz’ to begin!

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Why Rutherford used only gold foil in his famous gold foil experiment?

why didn't Rutherford use an aluminium foil, or a silver foil. Why he used gold foil in his gold foil experiment?

• atomic-physics

• 1 $\begingroup$ That's really a question you need to ask from Geiger and Marsden: en.wikipedia.org/wiki/Geiger%E2%80%93Marsden_experiment . It might have something to do with the fact that gold can be hammered into extremely thin foils, which is not possible (as far as I know) with either aluminum or silver. That reason is also given in the Wikipedia article. $\endgroup$ –  CuriousOne Commented Jun 5, 2016 at 10:01

4 Answers 4

He actually used also Aluminium, Silver, and Copper. He did so because he wanted to prove that the Rutherford cross section was proportional to $Z^2$.

In any case, he needed to use malleable material (metals) in order to achieve a micrometer-thin foil to prevent the entire $\alpha$ beam to be absorbed by the target.

• $\begingroup$ Hey this looks like a fantastic answer; can you give a citation for it? $\endgroup$ –  Selene Routley Commented Jun 5, 2016 at 12:55
• $\begingroup$ Professor Longo said it during the Nuclear Physics course at Sapienza university. The material used are cited also on Wikipedia's article: en.wikipedia.org/wiki/Geiger –Marsden_experiment I had forgotten one element:he used tin, too. $\endgroup$ –  Drebin J. Commented Jun 5, 2016 at 13:12

Is this true?

In a 1913 paper, The Laws of Deflexion of α Particles through Large Angles... Geiger and Marsden reused the above apparatus to measure how the scattering pattern varied with the square of the nuclear charge (i.e. if s ∝ Qn2). Geiger and Marsden didn't know what the positive charge of the nucleus of their metals were (they had only just discovered the nucleus existed at all), but they assumed it was proportional to the atomic weight, so they tested whether the scattering was proportional to the atomic weight squared. Geiger and Marsden covered the holes of the disc with foils of gold, tin, silver, copper, and aluminum. They measured each foil's stopping power by equating it to an equivalent thickness of air. They counted the number of scintillations per minute that each foil produced on the screen.

See Wikipedia

Yes, it is correct that Rutherford used other metallic atoms instead of gold. From using other metallic atoms, he drew the following conclusion that there shall be no change in his prior observations, if and only if the malleability of the metal is sufficive enough for the alpha particles to penetrate through, otherwise there shall be a lack of penetration of the alpha particles, thus different scattering of particles, which would ultimately for-go his previous experiment.

Geiger and Marsden first used Gold because it is a malleable metal and they could relatively easily produce foils of a thickness of around $1\; \mu$m which still is about 3500 atoms thick. Even so this was thin enough to observe an incoming alpha particle interacting with only one nucleus and not being absorbed by the foil.

Other malleable metals were then used to see what effect they had on the scattering of alpha particle. The parameter which they used to categorise a metal was its atomic weight as mentioned by @Mikhail in his question and they did find that the scattering was approximately proportional to the atomic weight squared.

It was Moseley who first systematically associated atomic number $Z$ with the number of positive charges in the nucleus.

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