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Content Benchmark P.8.A.7
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 Physical Science Matter P.8.A.1 P.8.A.2 P.8.A.3 P.8.A.4 P.8.A.5 P.8.A.6 P.8.A.7 P.8.A.8 Force and Motion Energy Content Areas Nature of Science (NOS) Life Science Earth Science Physical Science

Students know the characteristics of electrons, protons, and neutrons.   E/S

An effective tactic for teaching the fundamental particles of the atom is to illustrate the work of the men and women who uncovered them. Often the fundamental characteristics are simply listed in a table and students see them as discrete facts disconnected from their history. A timeline of historical events is seen in Figure 1.

Figure 1. Subatomic particles discovered between 1898 – 1964

The Electron: Discovery and Basic Properties
Electrons were first discovered by a British scientist, J. J. Thomson in 1897 while he was studying cathode rays.  Thomson found that the unusual rays he was studying were attracted to the positive end of a cathode ray tube.  He theorized that the rays were composed of particles which he called corpuscles and thought they would be the fundamental building blocks of the atom. Thomson was correct that his cathode ray particles were one of the particles that compose the atom. Later, these small particles were named electrons.

Figure 2. A simple cathode ray tube.
(From http://www.aip.org/history/electron/jjhome.htm)

Thomson continued experimenting with the cathode ray tube in order to determine some of the characteristics of the electron. Because the ray of electrons bent towards the positive electrode of the cathode ray tube, Thomson knew that the electron was negatively charged. He was unable to determine the precise mass of the electron, but did determine its charge to mass ratio.  Later, it was determined that the mass of the electron was 1/1836th the mass of a proton or 9.11 × 10−31 kg. The charge on a single electron is −1.602 × 10−19 Coulomb.

The electron is in the class of subatomic particles called leptons, which are believed to be fundamental particles of matter. Electrons are bound to the atom through electromagnetic attractions to positively charged protons. Electrons moving freely in a vacuum can be focused into a beam such as Thomson’s cathode ray tube.

Thomson proposed a theory that suggested that the atom was composed of a positive sphere of electricity with the electrons evenly spaced around it. This theory was called the “plum pudding” model of the atom.

The Proton: Discovery and Basic Properties
Ernest Rutherford was a student of Thomson and continued Thomson’s research of cathode ray tubes. In his famous gold foil experiment of 1911, Rutherford discovered positively charge particles inside the atom. Based on his experimental results, he formulated a new atomic theory that suggested that the atom consisted of a positive core with electrons surrounding this core.

Figure 3. Interpreting Rutherford’s Gold Foil Experiment
(From http://www.visionlearning.com/library/module_viewer.php?mid=50)

Further information on this topic and a diagram of the chamber used in his experiment can be found at http://www.rsc.org/chemsoc/timeline//pages/1911.html.

Characteristics of the proton include that it is positively charged, has a mass of 1.67×10−27 kg, and in terms of an atom, is located in the nucleus. The charge on a single proton is +1.602 × 10−19 Coulomb (exactly the same magnitude, but opposite in sign to a single electron). A hydrogen atom minus its electron (i.e., hydrogen ion) is also known as a proton.

The Neutron: Discovery and Basic Properies
The neutron was an elusive particle, and before it was discovered, its presence was predicted by Ernest Rutherford in 1920. He suggested that a neutral particle could be generated by the capture of an electron by a proton. He theorized that the particle was in the nucleus of the atom and that it had approximately the same mass as the proton, but did not carry a charge.

The scientist team of Irene and Frederick Joliot-Curie made an interesting discovery during one of their experiments, but misinterpreted the results. Although their experiment intrigued the science community, it was met with some skepticism. James Chadwick who worked in the Cavendish laboratory repeated Joliot-Curie’s experiment and re-interpreted the results suggesting the observations made by Joliot-Curie were actually due to a neutral particle which was a component of the radiation being emitted by a beryllium metal. He called the particle a neutron and received the Nobel Prize in 1935 for his work. The neutron has approximately the same mass as a proton, carries no charge, and is located in the nucleus of an atom.

A full explanation of this experiment can be found at
http://www.chemcases.com/nuclear/nc-01.htm.

A nice animation is available through http://wwwoutreach.phy.cam.ac.uk/camphy/neutron/neutron2_1.htm
and, http://web.visionlearning.com/custom/ chemistry/animations/CHE1.2-an-atoms.shtml.

Figure 4. Model of the atom based on Chadwick’s discovery.
This model is often called the Rutherford-Bohr Model of the Atom.
(From http://library.thinkquest.org/27954/neutron.html)

Summary-Characteristics of Sub-Atomic Particles

 Location Relative Charge Relative Mass (amu) Electron Outside nucleus -1 1/1836th Protons Inside nucleus +1 1 Neutrons Inside nucleus 0 1

Protons and neutrons do not have exactly the same mass as each other. On the carbon-12 scale, a proton has a mass of 1.0073 atomic mass units (amu) and a neutron has a mass of 1.0087 amu.

Relative Size of Sub-atomic Particles
The radius of a hydrogen atom consisting of one electron and one proton is approximately 5 × 10−9 meters.  The nucleus is approximately 1 × 10−15 meters in diameter. The "classical" radius of a "free" electron is taken to be about 3 × 10−15 meters, and the "classical" radius of a "free" proton is taken to be about 1 × 10−15 meters.

This information was obtained from the following site, which also contains more details about atomic and subatomic sizes see

Modern Models of the Atom
The modern model of the atom is a probability model in which electrons are located in charge clouds outside the nucleus of the atom, which contains the protons and neutrons (nucleons). The Standard Theory of the Atom includes discussions of smaller building blocks of matter: quarks, force carrier particles, and leptons.  Electrons are leptons and both protons and neutrons are composed of combinations of quarks.

A final site that summarizes the characteristics of protons, neutrons and electrons can be found at http://web.jjay.cuny.edu/~acarpi/NSC/3-atoms.htm.
For another helpful website which contains the history of the atom in paragraph form and which is also available in Spanish, please visit http://www.visionlearning.com/library/module_viewer.php?mid=50.

Nuclear Symbols
Nuclear symbols were developed as a model to represent the numbers of protons, neutrons and electrons in an atom.

Figure 5. Nuclear symbol for Helium
(From http://dbhs.wvusd.k12.ca.us/webdocs/AtomicStructure/Nuclear-Symbol.html)

Figure 6. Nuclear Symbol for Uranium
(From http://dbhs.wvusd.k12.ca.us/webdocs/
).

The mass number of an element represents the total number of protons and neutrons in an atom. The mass number is sometimes referred to as the A number. The atomic number represents the total number of protons in an atom. It is also known as the Z number.  In neutral atoms, the atomic number is the same as the total number of electrons in the atom. In the example of uranium-238, there are 92 protons, 92 electrons and 146 neutrons.

To assist students in calculating the numbers of protons, neutrons and electrons in different atoms, http://science.widener.edu/svb/tutorial/protons.html provides an interactive table for them to complete.

Content Benchmark P.8.A.7

Students know the characteristics of electrons, protons, and neutrons.   E/S

Common misconceptions associated with this benchmark

1. Students incorrectly think that there is an edge, or boundary, to an atom.

Atoms and orbitals have no hard edges. Instead, the contour of the orbital, as we show it in pictures and models, corresponds to the space of highest probability for electron location. Care must be taken during classroom instruction to discuss the strengths and limitations of models. Ask students to draw and interpret a model of the atom. From their interpretations, the teacher can address the misconceptions. Using vocabulary such as “electron shell” reinforces this misconception. Explain to students that some vocabulary does not reflect the current understandings of the atom and has its basis in the history of the atom.

This information was obtained from http://intro.chem.okstate.edu/ChemSource/Atomic/concpt4.htm.

Figure 7. The Fuzzy Atom
(From http://www.uq.edu.au/_School_Science_Lessons/TWFig4.GIF)

and, http://www.uq.edu.au/_School_Science_Lessons/TWImagesatoms.html.

2.  Students incorrectly think that air exists between particles (protons, neutrons, and electrons) in atoms.

There is no matter, air or otherwise, between atomic particles, because these particles are the matter from which air and all other gases is comprised. This common misconception can be addressed by building models that are more representative of the charge cloud model of the atom rather than “ball and stick” images.

3. Students incorrectly think that all atoms are charged.

Atoms are neutral because there are equal numbers of electrons and protons. Ions of atoms form when the atom gains or loses electrons and ions have a net positive or negative charge. Protons cannot be lost by an atom in normal chemical reactions. It is helpful to use the nuclear symbols of atoms to assist students in understanding that an equal number of electrons and protons exist in an atom. A simplified discussion of cations and anions can help students understand what charges are.

4. Students incorrectly think that all models accurately describe the atom.

Models are ways for us to understand the physical world. They are simplified representations. Models may have limitations, which can often cause misconceptions.  As scientific research finds new evidence, models are modified. But, regardless of the model, all do not fully represent reality.

and, http://www.regentsprep.org/Regents/physics/phys05/catomodel/default.htm.

Content Benchmark P.8.A.7

Students know the characteristics of electrons, protons, and neutrons.   E/S

Sample Test Questions

1st Item Specification: Know the structure of the atom.

Depth of Knowledge Level 1

1. Which of the following are transferred or shared when two atoms react chemically?
1. Electrons
2. Protons
3. Neutrons
4. Nucleons
1. Looking at a model of the atom, particles located within the nucleus that are positively charged are called
1. electrons.
2. protons.
3. neutrons.
4. nucleons.
1. Looking at a model of the atom, particles located within the nucleus that have a no charge are called
1. electrons.
2. protons.
3. neutrons.
4. nucleons.
1. Protons and neutrons together are known as
1. electrons.
2. protons.
3. neutrons.
4. nucleons.
1. The number of protons in a neutral atom is equal to the number of
1. ions.
2. isotopes.
3. electrons.
4. neutrons.

Depth of Knowledge Level 2

1. Cobalt (atomic number 27) is necessary for growth and is present in vitamin B12. The only naturally occurring isotope of the element cobalt has a mass number of 59. How many neutrons are in cobalt?
1. 86
2. 59
3. 32
4. 27
1. Calcium (atomic number 40) is an element needed for the development of bones and teeth in humans. How many electrons does a neutral atom of calcium contain?
1. 0
2. 20
3. 40
4. 60
1. In an atom, which force holds the protons and neutrons together in the nucleus?
1. The gravitational force.
2. The electromagnetic force.
3. The strong force.
4. The weak force.
1. Below are four diagrams representing atoms. Use the diagrams below to answer the following question.
 Nucleus Nucleus Nucleus Nucleus Figure A Figure B Figure C Figure D

Which of the following diagrams represents the size of the nucleus in comparison to the size of the atom?

1. Figure A
2. Figure B
3. Figure C
4. Figure D
1. In the Bohr model of the atom, electrons are
1. located in the nucleus.
2. located in oval rings around the nucleus.
3. located in distinct orbitals around the nucleus.
4. located in a probability cloud around the nucleus.

2nd Item Specification: Know the electrical charges of electrons, protons, and neutrons.

Depth of Knowledge Level 1

1. The overall charge on an electron is
1. +1
2. +2
3. 0
4. -1
1. The overall charge on a neutron is
1. 0
2. +1
3. +2
4. +3
1. The overall charge on a proton is
1. -1
2. 0
3. +1
4. +2
1. The overall charge when one electron and one proton are present in an atom is
1. -1
2. 0
3. +1
4. +2
1. The overall charge when an atom contains one proton and one neutron is
1. -1
2. 0
3. +1
4. +2

Depth of Knowledge Level 2

1. Which of the following would most likely experience repulsion?
1. Two electrons coming into contact with each other.
2. Two neutrons coming into contact with each other.
3. A neutron and a proton coming into contact with each other.
4. A proton and an electron coming into contact with each other.
1. When a plastic rod is rubbed with fur, the plastic rod becomes negatively charged. Which statement explains the charge transfer between the plastic rod and the fur?
1. Protons are transferred from the plastic rod to the fur.
2. Protons are transferred from the fur to the plastic rod.
3. Electrons are transferred from the plastic rod to the fur.
4. Electrons are transferred from the fur to the plastic rod.
1. The overall charge on an atom with 2 electrons, 3 protons, and 3 neutrons is
1. -1
2. 0
3. +1
4. +2
1. Use the image below to answer the following question.

If the two pith balls both have negative charges, the pith balls will

1. attract each other, but remain apart.
2. attract each other and stick together.
3. repel each other and stay apart.
4. neither repel or attract.
1. Use the image below to answer the following question.

If the two pith balls have opposite charges, the pith balls will

1. attract each other, but remain apart.
2. attract each other and stick together.
3. repel each other and stay apart.
4. neither repel or attrac

3rd Item Specification: Know the relative size of electrons, protons, and neutrons compared to the overall atom.

Depth of Knowledge Level 1

1. Which of the following is the SMALLEST of the sub-atomic particles?
1. Proton
2. Neutron
3. Electron
4. Nucleon
1. Which of the following are most similar in mass?
1. Proton and electron
2. Proton and cation
3. Neutron and electron
4. Proton and neutron
1. Which of the following contributes to the mass of the nucleus?
1. Protons and electrons
2. Protons and cations
3. Neutrons and electrons
4. Protons and neutrons
1. Which of the following contributes to the mass outside the nucleus?
1. Protons
2. Electrons
3. Neutrons
4. Nucleons

Depth of Knowledge Level 2

1. The mass number of an element is the total number of protons and neutrons located in the nucleus. If carbon has an atomic number of 6 and a mass number of 12, how many neutrons does it contain?
1. 0
2. 6
3. 12
4. 18
1. If the mass number of an element is the total number of protons and neutrons located in the nucleus, how many protons does chlorine have if its atomic number is 17 and its mass number is 35?
1. 35
2. 18
3. 17
4. 0
1. An atom has equal numbers of protons, neutrons and electrons. Which particle has the least effect on its mass?
1. Neutron
2. Proton
3. Electron
4. Nucleon
1. The substance sodium is abundant in the ocean as an ion dissolved in water. In order for an atom to become an ion which of the following needs to occur?
1. Electrons are lost or gained.
2. Protons are lost or gained.
3. Neutrons are lost or gained.
4. Nucleons are lost or gained.
1. Use the diagram below to answer the following question.

The mass number is the number of protons and neutrons in an atom. How many protons does the element, lithium, contain?

1. 3
2. 4
3. 7
4. 10
1. Use the diagram below to answer the following question.

The mass number is the number of protons and neutrons in an atom. How many neutrons does the element, lithium, contain?

1. 3
2. 4
3. 7
4. 10

Constructed Response P.8.A.7

1. The diagram below depicts Rutherford’s model of the atom. Use this diagram to answer the following questions.

1. Early atomic theories posed in the late 19th and early 20th centuries focused on including discoveries of sub-atomic particles. On such model was developed by Rutherford. List the basic principles of the Rutherford model of the atom.
2. The following diagram shows Rutherford’s famous gold foil experiment. Use this diagram to answer the question below.

Describe the experimental evidence Rutherford used to develop his model and why this explains how he developed the model.

Content Benchmark P.8.A.7

Students know the characteristics of electrons, protons, and neutrons.   E/S

1. A, DOK Level 1
2. B, DOK Level 1
3. C, DOK Level 1
4. D, DOK Level 1
5. C, DOK Level 1
6. C, DOK Level 2
7. C, DOK Level 2
8. C, DOK Level 2
9. D, DOK Level 2
10. C, DOK Level 2
11. D, DOK Level 1
12. A, DOK Level 1
13. C, DOK Level 1
14. B, DOK Level 1
15. C, DOK Level 1
16. A, DOK Level 2
17. D, DOK Level 2
18. C, DOK Level 2
19. C, DOK Level 2
20. B, DOK Level 2
21. C, DOK Level 1
22. D, DOK Level 1
23. D, DOK Level 1
24. B, DOK Level 1
25. B, DOK Level 2
26. C, DOK Level 2
27. C, DOK Level 2
28. A, DOK Level 2
29. A, DOK Level 2
30. B, DOK Level 2

Constructed Response 3-point Answers and Score Rubrics:

 3 points Response addresses all parts of the question clearly and correctly. Student response indicates that the atom consists of positive and negative charges, that the positive charges are located in the nucleus, that negatively-charged electrons are located outside the nucleus, and that most of the atom’s mass is located in the nucleus. Students should describe the experimental evidence that Rutherford used when he passed alpha particles (or massive positively-charged particles) through gold foil. Student responses should indicated that most of the alpha particles passed straight through the foil indicating that the atom is mostly empty space. Students responses should say that some of the particles were deflected showing that negatively-charged electrons exist in the outer regions of the atom. The student response should also indicate that a very few particles where reflected straight back showing a very small and massive region was at the center of the atom. 2 points Response addresses all parts of the question and includes only minor errors. 1 point Response does not address all parts of the question. 0 point Response is totally incorrect or no response provided.

Content Benchmark P.8.A.7

Students know the characteristics of electrons, protons, and neutrons.   E/S

Intervention Strategies and Resources

The following is a list of intervention strategies and resources that will facilitate student understanding of this benchmark.

1. The Discovery of the Electron Exhibit

This site provides a museum presentation of the experiments by J.J. Thomson in 1897 that led to the discovery of a fundamental building block of matter. Historical images give the students and the teacher the feel for the laboratory equipment prevalent during the 1890’s.

To access these activities, go to http://www.aip.org/history/electron/.

2. Rutherford’s Experiment

This site provides a narration that explains the history of the atom and Thomson’s theory. Rutherford and his colleagues had tried to test Thomson’s theory by bombarding gold foil. The animation assists the student in viewing Rutherford’s experiment and his analysis of the experimental results.

To access these activities, go to
http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf.

3. Exploring Life at Bio dot Edu

This site contains a detailed essay and diagrams about the historical development of Rutherford’s atomic theory.  The essay begins with Becquerel’s discovery of radioactivity and leads the reader through his experiment complete with information not usually included in textbook descriptions of the famous Gold Foil Experiment. This is a great nature of science reading.

To access these activities, go to

4. Famous Experiments: The Discovery of the Neutron

This site provides a brief explanation of the work of scientists that led to James Chadwick’s discovery of the neutron. The diagrams nicely assist the student in understanding how Chadwick designed his experiment. The essay helps students understand how science works to nullify hypotheses which often lead to new discoveries.

To access these activities, go to
http://dev.physicslab.org/Document.aspx?doctype=3&

5. The Particle Adventure: The Fundamentals of Matter and Force

Students are engaged with an interactive site that explores modern understandings of the atom as compared to the more commonly known history of the discovery of the subatomic particles provided in most classrooms. This site developed by the Particle Data Group of Lawrence Berkeley National Laboratory tours quarks, neutrinos, antimatter, dark matter, etc. It is a great site for more in-depth discussions with students about the nature of the atom.

To access these activities, go to