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Content Benchmark P.8.A.8
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Physical Science
Matter
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Force and Motion
Energy
Content Areas
Nature of Science (NOS)
Life Science
Earth Science
Physical Science

Students know substances containing only one kind of atom are elements which cannot be broken into smaller pieces by normal laboratory processes. E/S

Philosophers have long expressed differing ideas about the nature of matter. Even ancient cultures had developed elaborate beliefs about the origin and nature of matter (for example, the Greek idea that all things are made up of some combination of fire, water, air, and earth). Understanding the nature of elements seems easily comprehensible, but students often struggle with the concept that atoms are not divisible under ordinary laboratory conditions.


Figure 1. The Four Elements of Western Alchemy.
The figures shows how the four elements were imagined to combine in
various pairs to produce the "qualities" of hot, cold, wetness and dryness.
(From http://www.chem1.com/acad/webtext/intro/AT.html)

To learn more about the classic elements and how they contributed to the development of chemistry, go to http://web.lemoyne.edu/~giunta/EA/CONTENTS.HTML.

Alchemists had begun experimenting with metals, ores, and other substances in their attempts to make precious metals and materials. They knew through their experimentation that substances could be broken down into simpler substance, but at some point those substances could not be further simplified. Most of the common elements had not been identified until the technology existed to decompose naturally occurring compounds. Seven elements that had been known since antiquity are shown below.

Fe

Ferrum

Cu

Cuprum

Ag

Argentum

Sn

Stannum

Au

Aurum

Hg

Hydrargyrum

Pb

Plumbum

Figure 2. Seven Elements Known Since Antiquity
(From http://www.vanderkrogt.net/elements/fecu.html)

To help students understand the basic nature of elements, it may be helpful to review John Dalton’s Atomic Theory, which included ideas that were revolutionary in his time.

  1. Matter is neither created nor destroyed in chemical reactions. In other words, in ordinary chemical reactions, atoms are rearranged but never destroyed. To learn more about the conservation of mass, please go to MS TIPS Benchmark P.8.A.5.
  2. Compounds are composed of a definite number of atoms in a specific ratio. The masses of each of the elements in a compound are always the same. Elements in a compound are always present in the same proportions by mass. To learn more about compounds, please go to MS TIPS Benchmark P.8.A.4.
  3. Elements may combine with each other in different ratios to make different compounds but the differences in mass are always whole number differences. To learn more the relationships among compounds, please go to
    MS TIPS Benchmark P.8.A.4.

Dalton understood that atoms could not be further subdivided in ordinary chemical reactions. His theory helped chemists organize their understandings of matter. The concept map below provides a road map for students beginning their studies of atoms, elements, compounds and their characteristics.

Figure 3. Concept Map of Elements
(From http://www.chem1.com/acad/webtext/intro/AT.html)

Further readings about the history of elements can be found at http://www.chem1.com/acad/webtext/intro/AT.html.

Elements are substances composed of one type of atom containing a specific number of protons. Henry Moseley (1887-1915) identified the atomic number of an element as the fingerprint of an element. This idea was revolutionary and provided support for Dalton’s Atomic Theory. As a result the idea emerged that all atoms of an element contain the same number of protons. Atoms interact with each other in chemical reactions by transferring electrons. In this way, new compounds are formed.

It may be helpful to use some different models to help students understand this concept. M&M’s of one color could be used to demonstrate atoms of an element, but the analogy is limited and students should be queried as to the strengths and weaknesses of the model. Another analogy that could be used is a bag of sticky white marshmallows where each marshmallow represents an atom of an element, but the stickiness helps keep them bound together in the element; again, students should be queried for the strengths and limitations of the model. Finally, students could be prompted to make paper models of atoms of different elements writing the number of protons in the center of their model. Students should identify why their models effectively represent atoms of an element and should demonstrate through manipulation of their models how chemical reactions form new substances.

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Content Benchmark P.8.A.8

Students know substances containing only one kind of atom are elements which cannot be broken into smaller pieces by normal laboratory processes. E/S

Common misconceptions associated with this benchmark

1.  Students incorrectly think that the Law of Conservation of Mass does not apply to atoms.

Students may be able to repeat the Law of Conservation of Mass, but see no problem with atoms disappearing or appearing to balance equations. Conceptually students understand the idea of balancing equations, but when asked to write equations, they systematically remove or add atoms revealing their misconception.  One of the best ways to address this misconception is to have students use models (manipulatives) to account for atoms on both the reactant and product sides of the equation.

To learn more about this misconception and other science misconceptions, go to http://www.middleschoolscience.com/balance.html.


2. Students incorrectly assume that elements can form other elements.

Several students when questioned about the appearance of copper on magnesium ribbon in copper sulfate remarked that the brown solid came from the magnesium. They thought it was somehow present in the magnesium even though they agreed that magnesium was an element.

Using online demonstrations or videos demonstrating reactions will assist helping students gain experience with this concept. Major difficulties in this misconception reside in student inexperience with chemical reactions. Showing the demonstration and having students explain using scientific evidence will bolster their understandings.

To learn more about this misconception and other science misconceptions, go to http://apps.exploratorium.edu/10cool/index.php?cmd=browse&category=4.


3. Students incorrectly using representations of elements can lead to misconceptions.

Students cannot easily visualize atoms of an element. Teachers need to be cognizant that models and pictures can lead to alternative ideas about the structure of matter. Figure 4, shown below, represents one way to assist students in developing abstract ideas about chemical reactions.
 
To learn more about this misconception and other science misconceptions, go to
http://intro.chem.okstate.edu/ChemSource/ChemRx/chemrx11.htm.


Figure 4. Pictures in the Mind.
(From http://intro.chem.okstate.edu/ChemSource/ChemRx/chemrx11.htm)

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Content Benchmark P.8.A.8

Students know substances containing only one kind of atom are elements which cannot be broken into smaller pieces by normal laboratory processes. E/S

Sample Test Questions

1st Item Specification: Identify that elements contain only one type of atom.

Depth of Knowledge Level 1

  1. Atoms of an element contain only one type of atom because they each contain the same number of
    1. Protons.
    2. Electrons.
    3. Neutrons.
    4. Nucleons.
  1. The atomic number of an atom is often called its fingerprint because the
    1. electrons are used in bonding.
    2. neutrons hold the nucleus together.
    3. number of protons is identical from atom to atom.
    4. number of protons and electrons never changes.
  1. A student wants to separate atoms of an element into different categories based on the number of protons. You suggest that this isn’t possible because the number of protons
    1. is always the same in an element.
    2. fluctuates wildly.
    3. is different after bonding.
    4. depends on the number of neutrons.
  1. A student wants to separate elements in a mixture based on the number of electrons each contains. You suggest that this isn’t possible because
    1. electrons and protons are attracted to each other.
    2. electrons are repulsed by other electrons.
    3. electrons can vary from atom to atom if they become ions.
    4. electrons are found in the nucleus.
  1. The modern periodic table is based on elements being arranged by their atomic number. This is because elements arranged according to atomic number have one more
    1. proton than the element before it.
    2. neutron than the element before it.
    3. anion than the element before it.
    4. cation than the element before it.

Depth of Knowledge Level 2

  1. Oxygen has an atomic number of 8 while chlorine has an atomic number of 17. The difference between oxygen and chlorine is that
    1. oxygen has double the number of electrons than chlorine.
    2. chlorine has 11 more protons than oxygen.
    3. chlorine has 9 more protons than oxygen.
    4. oxygen loses protons in physical changes.
  1. Isotopes are atoms of an element that contain varying numbers of neutrons in the nucleus. Which of the following is true?
    1. C-12 has more electrons than C-14.
    2. C-12 has more protons than C-14.
    3. C-12 has fewer electrons for bonding than C-14.
    4. C-12 and C-14 have the same number of protons.
  1. The mass number of an element is the number of protons and neutrons added together. Which of the following is true for nitrogen (mass number 14, atomic number 7) and oxygen (mass number 16, atomic number 8)?
    1. Nitrogen contains more electrons than oxygen.
    2. Nitrogen contains one less proton than oxygen.
    3. Nitrogen contains four more protons than oxygen.
    4. Nitrogen contains two less protons than oxygen.
  1. The mass number of an element is the number of protons and neutrons added together. Which of the following is true for carbon-13 (atomic number 6) and nitrogen-15 (atomic number 7)?
    1. Nitrogen contains more electrons than carbon.
    2. Nitrogen has 8 neutrons and carbon has 7 neutrons.
    3. Nitrogen contains two more protons than carbon.
    4. Nitrogen contains one less proton than carbon.

Constructed Response P.8.A.8

  1. The diagram below depicts an apparatus, where an electric current is passed through a beaker of water and two separate gases are collected. Use this diagram to answer the following questions.

    1. Design a laboratory method for identifying the nature of the gases.
    2. Describe the type of reaction illustrated by the diagram.
    3. Can the two gases be further broken down? Support your answer with evidence and explain why only two gases could be formed in this process.

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Content Benchmark P.8.A.8

Students know substances containing only one kind of atom are elements which cannot be broken into smaller pieces by normal laboratory processes.  E/S

Answers to Sample Test Questions 

  1. A, DOK Level 1
  2. C, DOK Level 1
  3. A, DOK Level 1
  4. C, DOK Level 1
  5. A, DOK Level 1
  6. C, DOK Level 2
  7. D, DOK Level 2
  8. B, DOK Level 2
  9. 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 gases must be oxygen and hydrogen, and that glowing splint can be inserted into the test tubes If a loud popping sound is heard, then the gas is hydrogen, or if the splint re-ignites, then the gas is oxygen. Student responses also indicate that the process is decomposition and the gases are pure elements which cannot be further broken down by this method.

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.

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Content Benchmark P.8.A.8

Students know substances containing only one kind of atom are elements which cannot be broken into smaller pieces by normal laboratory processes. 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. Chemical Reactions with Flash Animation

This site has a series of student developed animations that can assist students in understanding the basic types of chemical reactions. Students are able to view the animation as well as see the balanced chemical reactions. The teacher can help students understand that compounds rearrange their atoms to form different compounds, but can also decompose into its component elements. Please note that Flash™ will need to be installed on the computers for students to use this site.

To access these activities, go to http://www.marymount.k12.ny.us/marynet/stwbwk05/05hchemistry.html.


2. Learning to Read Chemical Equations 

This site provides an activity with template to help students read chemical equations by identifying their elements and counting the numbers of atoms of an element.  Although the Nevada State Science Standards do not specify that middle school students be able to balance equations, it is helpful for students to be able to identify the reactants and products and their respective coefficients.  This site will assist students in this process.

To access these activities, go to http://www.middleschoolscience.com/balance.html.


3. Classic Chembalancer

This site is for more advanced students who want to practice balancing equations. The interactive game lets students use the Law of Conservation of Mass to balance the compounds and elements in the equations.  

To access these activities, go to http://funbasedlearning.com/chemistry/chembalancer/default.htm.

More challenging equations can be found at http://funbasedlearning.com/chemistry/chembalancer3/ques2.htm.


4. Cartoon Chemistry

This is a site that provides a worksheet which visually helps middle school students understand different types of chemical reactions that occur. Students get the idea that elements cannot be broken down but through reactions form new substances with new characteristics.

To access these activities, go to
http://www.nclark.net/CartoonChemistry.doc.

5. Chemistry of Fireworks

Nova developed this site which asks students to consider the relationship between the electromagnetic spectrum and the atomic structure of an atom of an element. The discussion is helpful for students in the understanding that atoms of elements have their own characteristic spectrum and that when heated they produce the characteristic spectrum.

To access these activities, go to
http://www.teachersdomain.org/resources/phy03/sci/phys/matter/fireworkcol/index.html.

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Benchmark
Support Pages

Misconceptions:
Click Here
Sample Questions:
Click Here

Intervention Strategies & Resources:
Click Here

Benchmark Related Vocabulary

Atom
Copper
Element
H2O
Nitrogen
Oxygen
Substance