Hand out to each student a copy of the periodic table (
S-C-2_Periodic Table.pdf). Draw the following diagram of a carbon-13 atom on the whiteboard. Make it large enough for all students to see the individual parts of the atom.
Tell students, “Today we are going to talk about a very important part of Pennsylvania history when engineers and construction workers came together in 1937 and built the world’s first industrial atom smasher. The Westinghouse Atom Smasher, as it is called, is located in Forest Hills, just outside Pittsburgh, Pennsylvania. It hasn’t been used in over 50 years but when it was built it was considered state of the art!” Now hold up a picture of the Westinghouse Atom Smasher from the Web site: http://img.groundspeak.com/waymarking/display/236432f1-86f3-4d0b-b91c-4aede565f37f.jpg for everyone in the class to see (S-C-2-1_Atom Smasher.doc).
Tell the class, “Before we proceed further and talk more about the atom smasher, let’s talk about what the scientists were trying to smash. Can anybody tell me what I have drawn on the whiteboard?” Ask for a show of hands. Most students will say that an atom has been drawn. Then ask them, “But what type of atom have I drawn?” Some students might say that they need to know more about the atom first; for example, which of the particles shown in the diagram are protons. Tell the class, “The protons are shaded black” and draw a key, labeling a shaded black circle as a proton. Tell students, “The proton has a +1 charge.” A student might then say that the model shows a carbon atom. Compliment the student for his or her correct answer, or if no one knows the correct answer say to the class, “We have an example of an atom which has six protons. The atomic number is equal to the number of protons, so, looking at the periodic table, we see that the element carbon in group 14 has an atomic number of 6. Notice that by counting the protons or the number of electrons (for a neutral atom) we can find the element on the periodic table and even predict some of its properties.”
Next ask students, “What are the rest of the particles shown here in my model of the atom?” Allow students to think for about 10 or 15 seconds and then have them identify the remaining subatomic particles. Say, “As you can see, we have another particle with red shading in the center of the carbon atom.” Draw a circle shaded red in the key and label it as a neutron on the whiteboard. Say, “This particle is called a neutron because it has no charge (or is neutrally charged). This particle was discovered in 1932 by James Chadwick. The protons and neutrons make up the nucleus of the atom. Believe it or not, scientists did not even know that atoms had nuclei until Ernest Rutherford fired alpha particles at some gold foil in 1909. He later theorized that most of the mass of the atom lay in the center of the atom in a small, very dense nucleus. The rest of the atom consists of mostly empty space.”
Now ask students about the smaller particles moving around the outside of the nucleus. Say, “These particles are called electrons. They were discovered in 1897 by J.J. Thomson.” Draw a much smaller circle shaded blue in the key and label it as an electron on the whiteboard. “These particles are much smaller than the protons and neutrons and have about 1/2000th the mass of a proton or neutron. They also have a −1 charge, the opposite of the charge on a proton. Niels Bohr along with Ernest Rutherford theorized that these electrons orbited the nucleus of the atom. This is not an entirely accurate model, now that we have the Quantum model of the atom, but it is still a good starting point for our discussion of the Westinghouse Atom Smasher.” At this point, the picture on the whiteboard should look similar to the following diagram:
Say, “I am now going to read the article, ‘Milestones: Westinghouse Atom Smasher, 1937’ so you can hear more about the atom smasher.” (The article is located at: http://www.ieeeghn.com/wiki/index.php/Milestones:Westinghouse_Atom_Smasher,_1937)
Make sure the class knows the vocabulary that describes some of the parts of the atom smasher. For example, explain, “A vacuum tube is an electronic device that contains an arrangement of electrodes (or metal plates). These electrodes are in a glass or metal tube in which virtually all the air has been removed. The Van de Graaff generator is an electrical device that produces high voltages (5 million volts or over 40,000 times the voltage used in our homes). These high voltages are produced by a rapidly moving belt rubbing against a hollow metal sphere. This produces an enormous amount of static electricity. The voltage set up by this static electricity accelerates subatomic particles or atom fragments down the vacuum tube, causing them to smash into their target. Some of these fragments travel from 30 million to 100 million miles per hour (5 – 15% of the speed of light) giving them a lot of kinetic energy! This large amount of energy enables the speeding particles to break the target atoms into many pieces, giving off radiation. Now let’s be like these target atoms and break into groups!”
Break the class into four groups for each research project. Send each group to a computer station or laptop computer set up on a lab table. Tell students, “The first group will be called ‘Dalton’s Group.’ You will go on the Internet and research Dalton’s model of the atom. Your task will be twofold:
1. Describe and draw the model of the atom proposed by John Dalton.
2. Use some creative thinking to predict what would happen to a target atom in the Westinghouse Atom Smasher if John Dalton’s theory was correct.
The second group will be called ‘Thomson’s Group.’ You will also have two tasks using the Internet:
1. Describe and draw the model of the atom proposed by J.J. Thomson.
2. Think creatively and describe what you think would happen to J.J. Thomson’s atom if it was the target in the Westinghouse Atom Smasher.
The third group will be called ‘Rutherford’s Group’ and you will have two tasks. Go on the Internet and:
- Describe and draw the model of the atom proposed by Rutherford.
- Describe what might happen if Rutherford’s atom got smashed in the Westinghouse Atom Smasher.
Last but not least, the fourth group, called ‘Bohr’s Quantum Group’ will have these two tasks, which will be carried out using the Internet:
- Describe and draw the modern model of the atom which came into view after Bohr proposed his model in 1913, James Chadwick made his discovery in 1932, and later scientists made their discoveries leading to the modern atomic theory.
- Imagine and describe what might happen to this modern atom if the accelerated particles in the Westinghouse Atom Smasher targeted this atom.”
Give students about 20 minutes to work and then have each group choose a presenter to communicate their findings. Each presenter should orally describe the scientist’s model of the atom and then show a drawing to the class. Then the presenter should share what might happen to such an atom in the Westinghouse Atom Smasher. Possible responses from each group are shown below. If a group’s response is incorrect or unclear, share the responses and show the pictures given below.
Dalton’s Group:
- Say to students, “Dalton said that all matter is made up of atoms. These atoms cannot be broken up into smaller particles because they are indestructible. His model probably looked like this.” On the whiteboard show a model that looks like this:
- “If this atom were put in the atom smasher, nothing would happen to it. It would just ricochet around like a billiard ball being hit by another ball.”
Thomson’s Group:
- Now say, “Thomson thought atoms were like plum pudding in that you had pudding (the matrix of the atom), which had a positive charge, and plums (the electrons), which had negative charges, all mixed through the pudding. His model probably looked like this.” On the whiteboard show a model that looks like this:
- “If this atom were put in the atom smasher, it would probably knock the electrons out of the matrix, leaving just the positive matrix behind, or it might create many smaller globules of the matrix containing just an electron or two.”
Rutherford’s group:
1. Next say, “Rutherford theorized that the atom had a central positive core (nucleus) surrounded by negatively charged electrons orbiting around the core (nucleus) like planets around the Sun. He suggested that the tiny core (nucleus) of the atom contained almost all of the atom’s mass, while the rest of the atom was mostly empty space. His model probably looks like this.” On the whiteboard show a model that looks like this:
2. “If this atom were put in the atom smasher, the core (nucleus) might remain intact but be stripped of its electrons, or the core (nucleus) might be split into smaller positive particles.”
Bohr’s Quantum Group:
- Finally say to the class, “Bohr came up with the idea that electrons were quantized; that is the energy of the electrons in the atom was restricted to certain discrete values. This prevented electrons from losing energy and spiraling into the nucleus. Later scientists theorized that positively charged protons and neutrally charged neutrons made up the nucleus, while electrons existed in probability clouds about the nucleus rather than traveling in circular orbits. The model for a very simple atom like hydrogen or helium probably looks like this.” On the whiteboard show a model that looks like this (the fuzziness may be difficult to replicate, so different colored bands might be used to represent different degrees of probability instead):
- “If this atom were put in the atom smasher, the nucleus would probably disintegrate and atoms of different elements would be formed. Even the protons and neutrons might disintegrate forming even smaller subatomic particles. Also a lot of energy would probably be given off in the form of dangerous radiation.”
Extension
- Provide students requiring more practice with the standards, an alternative atomic model project. This assignment may include:
o a verbal presentation to the teacher only
o limited assignment with specific sections omitted
o creation of a diagram/picture in place of verbal presentation
- For students performing above and beyond the standards, hand out photocopies of the article “Sharpshooting at the Atom” by E.U. Condon, which appeared in the July 1940 edition of Popular Mechanics Magazine. For homework, have each student read the article and write a one to two-page summary answering the following questions:
o Why was the Westinghouse Atom Smasher built?
o How did the atom smasher work?
o What kind of fast-moving particles were being aimed at the target?
o How were particles resulting from the collisions detected?
o What did scientists at that time hope to learn from their results?
Pick up the summaries, make comments on them, and return them the following day.