Chemistry Independent Project

Student Name: ______School Name:______Teacher Name:______

Hello Students,

This resource packet includes a project that you can work on independently at home. You should also have project packets for some of the other courses you are enrolled in. These projects are standards-aligned and designed to meet the Remote Learning instructional minutes guidelines by grade band. High School Chemistry Project: Which model of the atom is best supported by evidence?

Estimated Time ~225 minutes

HS PS1-1 Use the periodic table as a model to predict the relative properties Grade Level of elements based on the patterns of electrons in the outermost energy level Standard(s) of atoms.

Caregiver Support Caregivers can support by assisting students with reading and analysis of Option data.

Materials Needed Writing Utensil, Paper/Notebook

Question to Explore Which model of the atom is best supported by evidence?

Student Directions Detailed directions are given in the task.

Images of the Models of the Atom Adapted From: Compound Chem Investigation 1 Table Adapted From: Concord Consortium Interactions Investigation 2, Experiment 1 Data Adapted From: Concord Consortium Interactions Investigation 2, Experiment 4 Text Adapted From: Wired - The Development of the Model of the Atom Investigation 2, Experiment 5 Text Adapted From: Universe Today

Introduction As you may have seen in your chemistry coursework so far, all things are made of very, very small particles, which we call atoms. That’s right. Everything. You, your parents, your backpack, the ground, your school, your neighbor’s dog, the sidewalk, rocks, the air we breathe, and everything else is composed of atoms. Scientists have long debated exactly what an atom is, what it looks like, and what are the smaller parts that might make up an atom. Over the last 200 years, they have come up with five different ideas for what an atom is and what makes it up.

The table below shows each of the different models of the atom that you will be evaluating.

0 Student Name: ______School Name:______Teacher Name:______Solid Sphere Plum Pudding Nuclear Model Orbital Model Electron Cloud Model Model Model

In this task, you will gather evidence from a series of experiments and use this evidence to evaluate the five different models of the atom. This will help you answer the driving question, “Which model of the atom is best supported by evidence?”

1. Based on your prior experience in your life or in science class, which model of the atom seems most familiar to you? When do you think you saw this model? Record your observations on a separate sheet of paper.

Part 1 - Features of Atoms

Atom Size Atoms are too small to be seen, but how small are they? In the table below, explore how atoms compare in size with various other objects you might study in science class. Because atoms are so small, you will use objects you can see to represent atoms and other small objects. These comparisons will help you understand how small atoms really are.

Atom DNA Virus The diameter of an atom While DNA can be quite The diameter of a virus is is approximately long, its diameter is about 0.00000012 m. 0.0000000001 m. approximately Actual Object & 0.0000000025 m. Size

1 Student Name: ______School Name:______Teacher Name:______One sprinkle is about 0.001 If an atom were as big as If an atom were as big as m in diameter (1 mm). a sprinkle, the diameter of a sprinkle, a virus would a strand of DNA would be be about the same size as Relative Size of similar to the diameter of a beach ball with a Everyday the handle of a broom diameter of 1 m. Objects If An (0.025 m). Atom Were A Sprinkle.

Red Blood Cell Strand of Hair Average Height of a 16 The diameter of a red A strand of hair is Year Old blood cell is about approximately 0.0001 m in 0.000006 m. diameter. An average 18 year old is 1.6 m tall. Actual Object & Size

If an atom were as big as If an atom were as big as If an atom were as big as a sprinkle, a red blood cell a sprinkle, a strand of hair a sprinkle, a 16 year old would have a diameter of would be about 10 would be about 16 million Relative Size of about 60 m. football fields across. meters (10,000 miles) tall, Everyday which is further than the Objects If An distance from Chicago to Atom Were A China. Sprinkle.

2. Which of the above analogies to the size of an atom most resonates with you? Why? 3. How many atoms do you think it would take to line up across a strand of hair? In terms of the analogy to sprinkles, how many sprinkles lined up do you think it would take to stretch across 10 football fields? You can estimate your response by stating what order of 10 (10, 100, 1000, 10,000, and so on) that you think is appropriate, or you can calculate the exact number based on the information in the table above. Record your response on a separate sheet of paper.

2 Student Name: ______School Name:______Teacher Name:______Atom Charge When trying to develop a model of the atom, scientists have often experimented with charge interactions. What do we mean by charge interactions? In experiments with electricity, particularly static electricity, Benjamin Franklin identified two types of electric charge: he called one positive electricity and the other negative electricity. These two types of electricity could explain much of our observations of static electricity, and therefore, perhaps give clues into what charge had to do with atoms.

You have likely heard the saying before that “opposites attract”. This is true for charges. Opposite charges will attract one another, and like charge will repel. The two types of electrical charges, positive and negative, are opposite types of charge. Thus, two negative charges will repel each other, two positive charges will repel each other, and a positive and a negative charge will attract each other. In order to better understand charge interactions, you will complete the experiment below using transparent tape (Scotch® Magic™ Tape). If you do not have access to transparent tape, you may skip to the experimental observation diagrams and answer the questions that follow.

Tape Experiment 1 A. Stick a 10 cm piece of transparent tape to your tabletop with about two cm hanging loose over the edge. B. Use your thumb or a finger to rub the tape against the tabletop so it is stuck very well. C. Stick a second 10 cm piece of tape next to this piece and again rub the tape against the tabletop so it is stuck very well. D. Pull up on the loose end and quickly lift the tape away from the top of your table, making sure not to get any of the tape stuck to itself. (If this happens, start over.) E. Pull the second piece up as you did the first in the previous step. F. Bring the non-sticky side of the first tape close to the non-sticky side of the second tape. 4. How do the pieces of tape behave as you bring the second close to the first? Record your observations on a separate sheet of paper.

Tape Experiment 2 A. Put a new piece of tape to your tabletop with about two centimeters hanging loose over the edge. B. Use your thumb or a finger to rub the tape against the tabletop so it sticks very well. C. Put another piece of tape exactly on top of the tape on the table, with a little part left unstuck (you will need to pull the pieces apart eventually, so keep a part of the top piece separate). D. Pull the set of two pieces of tape off of your lab table quickly. Rub the non-sticky side of this “2-piece-of-tape system” to something metal in your home. Do not let the tape touch anything else. E. Pull the two pieces of tape apart. F. Bring the non-sticky side of the first tape close to the non-sticky side of the second tape.

3 Student Name: ______School Name:______Teacher Name:______5. How do the pieces of tape behave as you bring the second close to the first? Record your observations on a separate sheet of paper. 6. On the diagrams below, draw in + signs or - signs on each piece of tape to indicate which charge you think each piece of tape has. Refer to the introduction text to help you. Explain both of your drawings on a separate sheet of paper Expected Tape Interactions

Tape Experiment 1 Tape Experiment 2

The two pieces of tape from part 1 should The two pieces of tape from part 2 should have repelled when brought close to each have attracted when brought close to each other. other.

Part 2: Gathering Evidence to Evaluate Models of the Atom Experiments 1 & 2: Thomson’s Cathode Rays In 1803, John Dalton proposed that atoms were simply solid spheres, like a billiards ball. Later, in 1897, J.J. Thomson completed a series of experiments to determine if there was more to the atom. In the experiment, a beam called a cathode ray shoots out particles towards two charged plates. No one knew the identity of these cathode ray particles? Were they solid, uncharged atoms? Were they some other type of particle with different properties? Thompson first wanted to know if those pieces of the atom were charged. To figure this out, he designed and carried out the experiment below. Experimental Setup Cathode Ray Data The images at right show two Trial 1: Top plate: − − − − − Bottom plate: + + + + + electrodes connected to a high voltage source that produces cathode rays. The cathode ray is being shot from the left to right in the images. Horizontal metal plates are pictured both above (top plate) and below (bottom plate) the cathode ray as it is shot. The metal plates can

4 Student Name: ______School Name:______Teacher Name:______be positively charged, negatively No charges on plates charged, or left with no charge.

Your job is to determine the charge of the cathode ray particles (the ray is composed of small particles, even though the image makes it look like a continuous beam) based on its interactions with the differently charged metal plates.

Trial 3: Top plate: + + + + + Bottom plate: − − − − −

7. What patterns or relationships do you notice in the data? Record your observations on a separate sheet of paper. 8. What is the charge of the particle that forms the cathode ray? What evidence do you have to support this? Record your observations on a separate sheet of paper.

After investigating the charge of the particles, Thompson decided to also investigate the size of the particles. Scientists at the time knew that atoms of different varieties had different relative masses. For example, Hydrogen had a mass of 1 atomic mass unit (amu), and carbon had a mass of 12 amu, indicating that carbon atoms were 12 times heavier than hydrogen atoms. Thompson was curious how the size of these particles in the cathode ray compared to the size of other atoms. To test this, he compared the behavior of the cathode ray particles when exposed to charged plates, as above, to the behavior of heavier atoms. His results are shown below.

5 Student Name: ______School Name:______Teacher Name:______Relative Size Experimental Observation Particle (amu = atomic mass units)

Cathode Ray ?

(-) Hydrogen 1 amu

(-) Lithium 7 amu

(-) Carbon 12 amu

9. What patterns or relationships do you notice in the data? Record your observations on a separate sheet of paper. 10. What does this data suggest about the size of the cathode ray particles, compared to the size of known atoms? What evidence do you have to support this? Record your observations on a separate sheet of paper. 11. Use the evidence that you found in Experiments 1 and 2 to evaluate two of the models of the atom: the solid sphere model and the plum pudding model. Record your evaluation on a separate sheet of paper.

6 Student Name: ______School Name:______Teacher Name:______Atom Image Description Is this model supported or Model refuted by the data in Name Experiments 1 and 2? Why?

Solid The atom is a solid particle or sphere Sphere that cannot be divided into smaller Model particles or pieces.

Plum The atom can be divided into a fluid Pudding (the “pudding”) and electrons (the Model “plums”). The fluid spreads out in the atom and is positively charged. The electrons are very tiny and negatively charged. Most of the atom is made of fluid.

Experiment 3: Rutherford’s Gold Foil In the 1910s, Ernest Rutherford made a big discovery related to the structure of atomic structure while studying a new area of interest, radiation. At the time of his experiments, the Plum Pudding Model represented the presumed structure of the atom. Rutherford was studying a specific kind of radiation: alpha particles. Alpha particles are positively charged particles, which are smaller than an atom. Rutherford shot these positively charged particles at a very thin sheet of gold foil. The positively charged particles were much smaller than gold atoms. His goal was to observe the angle at which alpha particles were scattered as they passed through a layer of atoms. He came up with two possible predictions for his results, which are captured in the diagrams below. Plum Pudding Atom Model With Diffuse Positive Alternative Atom Model With Concentrated Charge Positive Charge at the Center

7 Student Name: ______School Name:______Teacher Name:______

12. What do you notice is different about the path of the alpha particles in these predictions? What does this have to do with the charges present in the atom models?

After making these predictions, Rutherford carried out his experiments. The results are shown in the image and table below.

Observations Data

9,999 out of 10,000 alpha particles pass through the gold foil in a nearly straight pathway and hit the detector screen.

1 out of 10,000 alpha particles are deflected to the side and hit the detector screen.

13. What do you notice about the outcome of Rutherford’s experiment? Which of his two predictions does it most match with? Why? 14. Use the evidence that you found in Experiment 3 to evaluate two of the models of the atom: the plum pudding model and the nuclear model. Record your evaluation on a separate sheet of paper.

Atom Image Description Is this model supported or Model refuted by the data in Name Experiment 3? Why?

Nuclear The atom can be divided into a Model nucleus and electrons. The nucleus occupies a small amount of space at the center of the atom. The nucleus is dense and positively charged. The electrons circle around the nucleus. The electrons are tiny and negatively charged.

8 Student Name: ______School Name:______Teacher Name:______Most of the atom is empty space. Experiment 4: Bohr’s Light

15. The text below describes the experimental setup and the results of Niels Bohr’s experiments with light and the atom. As you read the text, annotate any ideas you can find that you think will help you understand more about what makes up the internal structure of an atom.

In the 1920s, Niels Bohr studied the interaction of light and matter. Around that time, various scientists had identified a major issue involving the stability of the nuclear model of the atom. According to electromagnetic theory, an accelerated electric charge (like an electron moving around the atom) will continuously release energy as it moves. If an electron continuously loses energy as it moves around the nucleus, eventually the electron would decrease in energy over time, causing the electron to begin to spiral toward the nucleus and eventually crash into the nucleus, collapsing the atom. This doesn’t happen, so there must be something else going on.

Bohr investigated what would happen if you investigated the components of light that make up different elements. To do so, he shined light through a prism so that he could see what colors make up the light. Below are the results of his experiment in working with a normal lightbulb and with electrically charged hydrogen gas.

The result for the lightbulb is what you might expect - white light is made of all colors of light. With the lightbulb, Bohr essentially saw what you see in a rainbow when sunlight is broken down into its component colors. However, with the hydrogen gas, much of the color present in the normal light was missing, and instead, he only saw very specific, narrow bands of light.

To explain this, Bohr came up with an idea about energy states of electrons in the atom. He thought that electrons in an atom would have defined energy states. When an electric current is passed through the hydrogen gas, some of the electrons in the hydrogen gas molecules move from their initial ground energy state to an excited state that is further away from their nuclei. When the electrons return to the ground state, they emit light energy of various wavelengths. Bohr suggested the revolutionary idea that electrons "jump"

9 Student Name: ______School Name:______Teacher Name:______between energy levels (orbits), that is, without ever existing in an in-between state. When an electron absorbs energy, it will jump to a higher orbital, further away from the nucleus. When an atom emits or loses energy, it will fall to a lower orbital, closer to the nucleus. This allows electrons to remain stable and prevents the issue with electrons crashing into the nucleus as could have been the case with the nuclear model of the atom.

16. What do you think you can conclude from this text about where to find electrons in an atom? Record your response on a separate sheet of paper.

Experiment 5: Chadwick’s Neutron In addition to discovering the nucleus of the atom, Rutherford also wondered what the nucleus may be made of. Through additional experiments, in 1910 James Chadwick determined that the nucleus of atoms was made of both positively charged particles, called protons, and neutral particles, called neutrons. What he was unsure of was the role that neutrons played in the nucleus of the atom.

To help figure this out, we will look at a series of hypothetical atom images in the table below. Depending on the composition of their nucleus, atoms can be unstable, which means they will break apart and cease to exist, or stable, meaning they can maintain their structure.

Number of Number of Number of Element Protons in Neutrons in Simulated Atoms Electrons Nucleus Nucleus

Lithium 3 0 3

Lithium 3 4 3

10 Student Name: ______School Name:______Teacher Name:______Number of Number of Number of Element Simulated Atoms Protons Neutrons Electrons

Carbon 6 0 6

Carbon 6 6 6

17. What patterns or relationships do you notice in these atoms in regards to if they are stable or unstable? 18. What do you think this data helps you conclude about the nucleus of an atom? 19. Use the evidence that you found in Experiment 4 and Experiment 5 to evaluate two of the models of the atom: the nuclear model and the orbital model. Record your evaluation on a separate sheet of paper.

Atom Image Description Is this model supported Model or refuted by the data in Name Experiment 4? Why?

Nuclear The atom can be divided into a nucleus Model and electrons. The nucleus occupies a small amount of space at the center of the atom. The nucleus is dense and positively charged. The electrons circle around the nucleus. The electrons are tiny and negatively charged. Most of the

11 Student Name: ______School Name:______Teacher Name:______atom is empty space.

Orbital The atom can be divided into a nucleus Model and electrons. The nucleus is at the center of the atom and contains protons and neutrons. The electrons circle around the nucleus in specific orbits. The electrons are tiny and negatively charged. Different electrons are in orbits at different distances from the nucleus. Most of the atom is empty space.

Experiment 5: Schrodinger and Probability Equations

In 1926, Erwin Schrödinger used a popular field of study, called quantum mechanics, to come up with a series of equations that described the likelihood of finding an electron in a certain position within an atom. These equations predict the likely position of the location of the electron based on a function of probabilities. What does this mean for the atom? To figure this out, we will investigate an analogy in which probability is also helpful: throwing darts at a dartboard.

When throwing darts, one goal can be to hit the bullseye in the center of the board. However, for the average dart thrower, that doesn’t happen very often. Say you threw 1000 darts and aimed for the bullseye every time. Where might all of those darts land? Where the dart lands has a lot to do with probability. In the diagram below, you will see the results of a simulation that threw over 1000 darts at a dartboard. The location each dart landed is indicated by a red dot.

20. What do you notice about the distribution of dart throws on the dartboard? Record your observations on a separate sheet of paper. 21. How can you describe the pattern you see in terms of probability? Record your observations on a separate sheet of paper.

With what you found in the dart analogy in mind, let’s return to Schrödinger’s equations that describe the atom. His equation that describes the electrons in the hydrogen atom can be transformed into a graph of the probability of finding an electron at a specific distance from the nucleus of the atom. This graph is shown below.

12 Student Name: ______School Name:______Teacher Name:______

22. What do you notice in the graph? How does this relate to what you found with the dart throwing results? Record your observations on a separate sheet of paper. 23. What do you think this probability map tells you about the locations of electrons in the hydrogen atom? Record your observations on a separate sheet of paper.

24. Use the evidence that you found in Experiment 5 to evaluate two of the models of the atom: the orbital model and the electron cloud model. Record your evaluation on a separate sheet of paper.

Atom Image Description Is this model supported or Model refuted by the data in Name Experiment 5? Why?

Orbital The atom can be divided into a Model nucleus and electrons. The nucleus is at the center of the atom and contains protons and neutrons. The electrons circle around the nucleus in specific orbits. The electrons are tiny and negatively charged. Different electrons are in orbits at different distances from the nucleus. Most of the atom is empty space.

Electron The atom can be divided into a Cloud nucleus and electrons. The nucleus Model is at the center of the atom and contains protons and neutrons. We can’t say exactly where the electrons are, but probability tells us they are more likely to be in specific areas, usually close to, but not

13 Student Name: ______School Name:______Teacher Name:______immediately next to, the nucleus. The electrons are tiny and negatively charged.

Part 3: Final Arguments for the Model of the Atom 25. Using all of the evidence you have gathered, choose one model of the atom that you think is most supported by the body of evidence you have now analyzed. The models of the atom are all summarized on the next page. Write a final argument that states which model you most support, at least three pieces of evidence that support this model, and reasoning that explains how and why you think this model is most supported. Finally, choose one alternative atom model and provide two pieces of evidence and reasoning that refutes this model.

Claim: Record which of the atom models you think is best supported by the evidence. Evidence: Record at least three pieces of specific and appropriate evidence from the experiments analyzed. Reasoning: Record how and why you think this atom model is most supported, including why the evidence you chose tells you what the internal structure of the atom looks like. Rebuttal: Record one alternative atom model and provide one piece of evidence and reasoning that refutes this atom model.

Solid The atom is a solid particle or sphere that cannot be divided Sphere into smaller particles or pieces. Model

Plum The atom can be divided into a fluid (the “pudding”) and Pudding electrons (the “plums”). The fluid spreads out in the atom and is Model positively charged. The electrons are very tiny and negatively charged. Most of the atom is made of fluid.

Nuclear The atom can be divided into a nucleus and electrons. The Model nucleus occupies a small amount of space at the center of the atom. The nucleus is dense and positively charged. The electrons circle around the nucleus. The electrons are tiny and negatively charged. Most of the atom is empty space.

14 Student Name: ______School Name:______Teacher Name:______Orbital The atom can be divided into a nucleus and electrons. The Model nucleus is at the center of the atom and contains protons and neutrons. The electrons circle around the nucleus in specific orbits. The electrons are tiny and negatively charged. Different electrons are in orbits at different distances from the nucleus. Most of the atom is empty space.

Electron The atom can be divided into a nucleus and electrons. The Cloud nucleus is at the center of the atom and contains protons and Model neutrons. We can’t say exactly where the electrons are, but probability tells us they are more likely to be in specific areas, usually close to, but not immediately next to, the nucleus. The electrons are tiny and negatively charged.

Final Reflection Questions 26. What did you learn in this activity about how scientists develop and refine models over time? 27. What new ideas do you have about atoms and matter in the world around you? 28. One surprising observation from our understanding of the model of the atom is that the vast majority of an atom is empty space. So if atoms make up all of the things in the world, most of the things you see, such as your desk, your pen, your phone, you, and your friends, are made up of empty space. Yet, we perceive them as solid objects. Why do you think this is? If you have access to the internet, read this article to find out more: https://theconversation.com/if-atoms-are-mostly-empty-space-why-do-objects-look-and-feel-s olid-71742