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Content Benchmark P.12.A.2
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Students know elements in the periodic table are arranged into groups and periods by repeating patterns and relationships. E/S

Some Historical Background about the Periodic Table
By 1869, 63 elements were known. Dmitri Mendeleev, who is considered by many to be the father of the modern periodic table, organized these elements by increasing atomic weight. When he also organized the elements in horizontal rows in a table, he saw patterns in the properties of the elements. However, in order for the patterns to be consistent from row to row, Mendeleev had to leave some blank spaces in his table. He predicted that elements would be discovered to fit in these blank spaces (which they later were). Even after leaving blank spaces on his periodic table, there were some inconsistencies in which the trends of properties did not match the trends in atomic weights.

It wasn’t until the early 1900s that Mendeleev’s inconsistencies were explained. Henry Mosely used X-rays to measure the number of protons in atoms of the known elements. When he arranged the elements in order of increasing atomic number (number of protons), the patterns in the properties of the elements were consistent from row to row in the table of elements. According to Mosely’s Periodic Law, there was a periodic recurrence of the properties of the elements when the elements were arranged in order of increasing atomic number.

Note: Many scientists attempted to organize the elements previous to Mendeleev’s attempt. For more information about the development of the periodic table, see http://www.wou.edu/las/physci/ch412/perhist.htm

The Organization of the Modern Periodic Table
The modern periodic table is organized by increasing atomic number (number of protons) into horizontal rows, called periods, and vertical columns, called groups or families.

 Figure 1. The modern periodic table (From http://gpc.edu/~pgore/PhysicalScience/periodic-table.gif)

Elements in the same column exhibit similar chemical behaviors and reactivities. The columns are called families because of this. Just as the members of human families tend to have some similar behaviors, elements in the same family behave similarly. For example, all group 1A metals react vigorously with water.

To see a demonstration of the vigorous reactions that group 1A metals have with water, go to http://chemed.chem.purdue.edu/demos/main_pages/9.1.html.

Columns are labeled in one of two ways: (1) a number/letter combination (as is shown in Figure 1 above) or (2) numbers only, 1 through 18, from left to right. Some groups/families have specific names. Using the first column naming convention, the elements in group 1A (with the exception of hydrogen, H) are called alkali metals. Group 2A elements are called alkaline earth metals. Group 7A elements are called halogens, and Group 8A elements are called noble gases.

Rows are called periods because physical and chemical properties repeat in each period. This is similar to the weeks on a monthly calendar. The days of the week change in the same manner on each row of the calendar just as the properties of elements change in similar ways across each row of the periodic table. The periods are labeled with numbers. Period 1 is the first row of the periodic table, period 2 is the second row of the periodic table, and so on.

It is often useful to understand other features of the organization of the periodic table. Elements on the periodic table can be generally organized as metals, nonmetals, and semimetals (metalloids). Metals are typically shiny, ductile, malleable, and good conductors of heat and electricity. Nonmetals are elements that do not have the properties of metals, and metalloids have some of the properties of metals and some of the properties of nonmetals. In Figure 1, the boxes containing symbols of metalloids are shaded purple. Metals are found to the left of the metalloids, and nonmetals are found to the right of the metalloids (although hydrogen is found to the left, it is a nonmetal).

The periodic table is also arranged into blocks: s, p, d, and f. These blocks are related to the subshells electrons fill within the electron cloud.

For more information about the blocks of the periodic table and how they relate to the organization of electrons in the electron cloud, see http://www.chemsoc.org/viselements/Pages/data/intro_patterns.html.

 Figure 2. The blocks of the periodic table (From http://www.mpcfaculty.net/mark_bishop/ periodic_table_blocks_alone.jpg)

Why Do Elements in The Same Group Have Similar Chemical Behaviors?
Atoms are made up of 3 subatomic particles: protons, neutrons, and electrons. Protons and neutrons are found in the nucleus of the atom, and electrons are arranged in shells within the electron cloud. The electrons that are in the shell furthest away from the nucleus (the outer-most shell) are called valence electrons. When two atoms approach each other in order to react, the first subatomic particles that come in contact are the valence electrons. For this reason, the number and arrangement of valence electrons determines how an element will behave chemically. Elements with the same number and arrangement of valence electrons exhibit similar chemical behaviors (react in similar ways).

The number of valence electrons can be determined from the element’s electron configuration. For the representative elements (those in the s and p blocks), the number of valence electrons is equal to the group number. For example, all elements in group 7A have 7 valence electrons and have similar chemical behaviors and properties. All elements in group 1A have 1 valence electron and have similar chemical behaviors and properties.

For a very detailed discussion of this topic, see http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch6/quantum.html

Periodic Properties
There are several properties that change as one moves up and down or right and left on the periodic table. These are called periodic properties. Some of these properties are described briefly below, but for more information about periodic properties, see http://www.dartmouth.edu/~genchem/0102/spring/6winn/PeriodicProp.html, http://antoine.frostburg.edu/chem/senese/101/periodic/ or http://intro.chem.okstate.edu/1314F00/Lecture/Chapter7/Lec111300.html

Atomic Radius (Size). Atomic radius is the distance from the center of the nucleus to the valence, or outer, electrons. Figure 3 shows atomic radius plotted against atomic number. The positions of the group 1A elements are marked. Although there are some exceptions, atomic radius generally decreases across a period and increases down a group (which can be seen by focusing on just the marked group 1A elements). That the size of atoms increases down a column makes sense to most students. The atoms get larger as the atoms have more protons, electrons, and neutrons.

 Figure 3. Atomic radius v. atomic number (From http://www.chemistry.org/portal/a/c/s/1/acsdisplay.html? DOC=sitetools%5Cperiodic_table.html#)

The trend across the periodic table makes less sense to students. Atomic radius decreases across a period because the valence electrons in a given period are all located in the same shell; however, the nuclear charge (number of protons in the nucleus) increases across the period. Moving from left to right across a given period, the valence electrons feel a stronger pull from the increased nuclear charge that pulls the valence electrons closer to the nucleus (atomic size decreases across the period).

Ionization Energy. Ionization energy is the amount of energy required to remove the most loosely held (outermost) electron from an atom in the gas state. The closer an electron is to the nucleus, the more difficult it is to remove because of the attraction between the negatively charged electron and the positively charged nucleus. For this reason, smaller atoms have higher ionization energies. Accordingly, ionization energy increases towards the top of a column and, in general, increases from left to right on the periodic table, as can be seen in Figure 4 (ionization energy v. atomic number).

 Figure 4. Ionization energy v. atomic number (From http://www.chemistry.org/portal/a/c/s/1/acsdisplay.html? DOC=sitetools%5Cperiodic_table.html#)

Electronegativity. Electronegativity is defined as the attraction an atom has for the shared electrons in a bond. In general, electronegativity increases toward the top of each group and from left to right across the periodic table (electronegativities are not reported for noble gas elements because they do not tend to form bonds with other elements). Figure 5 shows electronegativity plotted against atomic number (the positions of the group 1A metals are marked).

 Figure 5. Electronegativity v. atomic number (From http://www.chemistry.org/portal/a/c/s/1/acsdisplay.html? DOC=sitetools%5Cperiodic_table.html#)

Content Benchmark P.12.A.2

Students know elements in the periodic table are arranged into groups and periods by repeating patterns and relationships. E/S

Common misconceptions associated with this benchmark:

1. Students confuse atomic number with the number of valence electrons in an atom.

In a neutral atom, the total number of electrons is equal to the atomic number (number of protons). Valence electrons are those electrons found in the outermost shell of the electron cloud. The number of valence electrons can be found for any element on the periodic table by writing out the electron configuration for that element. For representative elements (those in the s and p blocks, groups 1A – 8A), the number of valence electrons an atom has is equal to the element’s group number. For example, oxygen, which is found in group 6A and has an atomic number of 8, has 6 valence electrons.

http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch8/index.php#valence

2. Students confuse periods (rows) and groups (columns).

Some students are not aware that columns are vertical and periods are horizontal. This is most likely due to a lack of knowledge about the nomenclature associated with the periodic table or students’ confusing the meaning of the words horizontal and vertical. Teachers should be aware of this potential confusion and check students’ understanding of the terms period and group by asking students questions such as “in which group is the element sulfur (S)?” or “in which period is the element calcium (Ca)?”

For a short, but clear discussion on periods and groups, go to
http://www.chem4kids.com/files/elem_pertable.html

3. Students incorrectly think that the larger the mass or atomic number of an atom, the larger the radius of the atom.

Atomic radius generally increases down a column in the periodic table, but it DECREASES across a period as valence electrons feel greater effective nuclear charge.

http://itl.chem.ufl.edu/2045_s00/lectures/lec_12.html

4. Students incorrectly think that the periodic table is arranged by increasing atomic weight.

The modern periodic table is arranged in order of increasing atomic number. In most cases, this order also corresponds to increasing atomic weight; however, there are cases in which an element with a lower atomic number has a higher atomic weight than an element with a higher atomic number (see, for example, argon, Ar, and potassium, K). Molar mass (atomic weight) can be visually graphed against atomic number on the American Chemical Society’s interactive periodic table: http://www.chemistry.org/portal/a/c/s/1/acsdisplay.html?
DOC=sitetools%5Cperiodic_table.html

5. Students believe that an element will have similar chemical behaviors to other elements that are found in the same region of the periodic table.

It is more correct to say that elements in the same group/family will have similar chemical behaviors. Elements that are found in the same groups/families (columns) have similar chemical behaviors because they have the same number and arrangement of valence electrons (the electrons that are involved in chemical reactions). Elements that are found in the same region of the periodic table may share physical properties. For example, oxygen (O) and nitrogen (N) are found in the same region of the periodic table. They are both considered to be nonmetals and, as such, have similar physical properties (they are both gases, not malleable, poor electrical conductors, etc.). Chemically, however, oxygen’s reactions are much more similar to those of sulfur (S), which is in the same group as oxygen, than they are to those of nitrogen.

http://educ.queensu.ca/~science/main/concept/chem/c07/C07CDTL1.htm.

Content Benchmark P.12.A.2

Students know elements in the periodic table are arranged into groups and periods by repeating patterns and relationships. E/S

Sample Test Questions

1st Item Specification: Explain why elements in the main groups (metals, nonmetals, alkali metals, alkaline earths, halogens, and noble [inert ] gases) on the periodic table have similar properties.

Depth of Knowledge Level 1

1. What is common among a family of elements?
1. Number of valence electrons.
2. Number of energy levels.
3. Shielding effect of electrons.
4. Amount of protons in the nucleus.
1. Why do elements in the same families (groups) on the periodic table have the same properties?
1. They have the same atomic number and mass number.
2. They have the same number of electrons.
3. They have the same number of valence electrons.
4. They have very similar mass and atomic numbers.
1. The alkali metals have similar properties due to the number of valence electrons and therefore they
1. are all in the same period on the periodic table.
2. are all in the same group on the periodic table.
3. all have the same number of electrons.
4. all have the same atomic number.

Depth of Knowledge Level 2

1. Elements in the same group on the periodic table have similar
1. mass numbers and atomic masses.
2. physical properties and mass numbers.
3. chemical properties and atomic masses.
4. chemical and physical properties.
1. Use the following periodic table to answer the question below.

Which of the following pairs share similar properties?

1. Bromine (Br) and Iodine (I)
2. Oxygen (O) and Iodine (I)
3. Fluorine (F) and Neon (Ne)
4. Helium (He) and Hydrogen (H)
1. Use the following periodic table to answer the question below.

Which of the following elements will react similarly to selenium (Se)?

1. Germanium (Ge)
2. Xenon (Xe)
3. Sulfur (S)
4. Titanium (Ti)
1. Which group of elements would be expected to have very similar properties?
1. Oxygen, sulfur, selenium.
2. Nitrogen, oxygen, fluorine.
3. Sodium, magnesium, potassium.
4. Neon, sodium, potassium.
1. When comparing the noble gas family and halogen family on the periodic table, which of the following statements is true about their chemical properties?
1. They are similar to each other because they are side by side on the periodic table.
2. They are different from each other because they are side by side on the periodic table.
3. They are similar to each other because they have the same number of valance electrons.
4. They are different from each other because the have a different number of valence electrons.

2nd Item Specification: Identify the positions of metals and non-metals on the periodic table.

Depth of Knowledge Level 1

1. Use the following periodic table to answer the question below.

Where are the metals located on the periodic table?

1. On the far right of the periodic table.
2. On the far left of the periodic table.
3. To the right of the metalloids.
4. To the left of the metalloids.
1. Use the following periodic table to answer the question below.

Where are the non-metals located on the periodic table?

1. On the far right of the periodic table.
2. On the far left of the periodic table.
3. In the middle of the periodic table.
4. Along the bottom of the periodic table.

Depth of Knowledge Level 2

1. The location of the metals and non-metals on the periodic table are because of their
1. valence electrons.
2. energy levels.
3. atomic mass.
4. atomic numbers.
1. Which of the statements below correctly describe where fluorine is located on the periodic table and why?
1. It is to the right of the metalloids because it is a metal.
2. It is to the left of the metalloids because it is a metal.
3. It is to the right of the metalloids because it is a non-metal.
4. It is to the left of the metalloids because it is a non-metal.

3rd Item Specification: Classify elements as metals and non-metals.

Depth of Knowledge Level 1

1. Which of the following are properties of metals?
1. Malleable, ductile, and good conductors of heat and electricity.
2. Malleable, dull, and good conductors of heat and electricity.
3. Ductile, shiny, and poor conductors of heat and electricity.
4. Ductile, malleable, and poor conductors of heat and electricity.
1. Which of the following are properties of non-metals?
1. Dull luster, ductile, and good conductors of heat and electricity.
2. Dull luster and poor conductors of heat and electricity.
3. Malleable, ductile, and good conductors of heat and electricity.
4. Malleable and poor conductors of heat and electricity.

Depth of Knowledge Level 2

1. Is Cobalt (Co) a metal or a non-metal and why?
1. It is a metal because it is dull and is a poor conductor of electricity.
2. It is a metal because it is ductile and is a good conductor of heat.
3. It is a non-metal because it is shiny and is a good conductor of electricity.
4. It is a non-metal because it is malleable and is a poor conductor of heat.
1. Is Chlorine (Cl) a metal or a non-metal and why?
1. It is a metal because it is in period four, is ductile and shiny.
2. It is a metal because it is on the right side of the periodic table and it is dull.
3. It is a non-metal because it is in period four and is ductile and a gas.
4. It is a non-metal because it is on the right side of the periodic table and is a gas.

4th Item Specification: Predict periodic trends in atomic mass and atomic number.

Depth of Knowledge Level 1

1. The periodic table is arranged in order of
1. protons lost.
2. electrons lost.
1. Atomic mass on the periodic table progressively changes left to right and top to bottom because
1. a proton is being lost.
2. an electron is being lost.
3. a proton is being added.
4. an electron is being added.

Depth of Knowledge Level 2

1. Use the following periodic table to answer the question below.

Since the element Cobalt(Co) is located to the right of Iron(Fe), which of the following can be predicted about its atomic mass and atomic number?

1. Cobalt has a lower atomic mass and atomic number than Iron.
2. Cobalt has a higher atomic mass and atomic number than Iron.
3. Cobalt has a lower atomic mass and higher atomic number than Iron.
4. Cobalt has a higher atomic mass and lower atomic number than Iron.
1. Use the following periodic table to answer the question below.

An element found in the upper right corner of the periodic table should

1. have a higher atomic number than Barium (Ba),
but a lower atomic mass.
2. have a higher atomic number and atomic mass than Barium (Ba).
3. have a lower atomic number than Barium (Ba), but a higher atomic mass.
4. have a lower atomic number and lower atomic mass than Barium (Ba).

5th Item Specification: Recognize the difference between the atomic number and the atomic mass of an element.

Depth of Knowledge Level 1

1. The atomic mass of an element represents the
1. average mass of all its known isotopes.
2. total mass of all its known isotopes.
3. the average mass of the protons and neutrons.
4. the total mass of the protons and neutrons.
1. The atomic number of an element represents the number of
1. protons.
2. neutrons.
3. nulceons.
4. valence electrons.

Depth of Knowledge Level 2

1. Which of the following explains the difference between atomic number and atomic mass?
1. The atomic number is the number of protons and the atomic mass is the average mass of the element’s known isotopes.
2. The atomic number is the number of protons and the atomic mass is the total mass of the protons and electrons.
3. The atomic number is the total number of protons and neutrons and the atomic mass is the average mass of the isotopes.
4. The atomic number is the total number of protons and neutrons and the atomic mass is the total mass of the protons and electrons.
1. Only two isotopes of copper exist in nature: copper-63 and copper-65. Which of the following is true?
1. The atomic mass for copper is the average of the two isotopes or 64 a.m.u.
2. The atomic mass for copper is the total mass of both isotopes or 128 a.m.u.
3. The atomic mass is the average of the abundances of the isotopes
of 63.45 a.m.u.
4. The atomic mass is based on the heaviest element and is 65.21 a.m.u.

6th Item Specification: Calculate the number of electrons, protons, and neutrons given the atomic number and atomic mass for a given isotope of any element in the periodic table.

Depth of Knowledge Level 1

1. How many protons are in an element with the atomic number of 25?
1. 5
2. 12
3. 13
4. 25
1. How many electrons are in a neutral atom with an atomic number of 12?
1. 4
2. 6
3. 12
4. 24

Depth of Knowledge Level 2

1. Use the table below to answer the following question.
 25 Manganese Mn 54.94 26 Element # 26 El ? 27 Cobalt Co 58.69

Which of the following could be the atomic mass of Element # 26?

1. 52.64
2. 54.0
3. 56.21
4. 63.98
1. Use the table below to answer the following question.
 48 Cadmuim Cd 112.41 ? Element X X ? 50 Tin Sn 118.71

Predict the properties for Element X?

1. It is a metal, atomic number 49, approximate average
atomic mass of 114.
2. It is a semi-metal, approximate average atomic mass
of 113, atomic number 49.
3. It is a non-metal, approximate average atomic mass
of 118, atomic number 49.
4. It is a gas, approximate average atomic mass
of 117, atomic number 49.

Content Benchmark P.12.A.2

Students know elements in the periodic table are arranged into groups and periods by repeating patterns and relationships. E/S

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

Content Benchmark P.12.A.2

Students know elements in the periodic table are arranged into groups and periods by repeating patterns and relationships. 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. Interactive Periodic Tables
There are a number of interactive periodic tables on the internet that can be used to help students learn about and visualize different periodic properties. Just a few are listed here.

a. Chemical & Engineering News Periodic Table
Each element in this periodic table is linked to an essay about the element and its properties. This periodic table was assembled to celebrate the 80th anniversary of C&E News.

To access this interactive table, go to http://pubs.acs.org/cen/80th/elements.html

b. American Chemical Society Periodic Table
Each element in this periodic table is linked to a list of elemental properties. There are also tabs in which an elemental symbol can be clicked to show the element’s orbital diagram and in which periodic properties can be plotted against atomic number.

c. Dartmouth Periodic Table
The boxes in this periodic table can be shaded different colors to show changing periodic properties.

This table is found at http://www.dartmouth.edu/~chemlab/info/resources/p_table/Periodic.html

2. Periodic Table Videos
This series of videos from Georgia Public Broadcasting discusses the periodic table. There are 3 videos: one about the history of the periodic table, one about the organization of the periodic table, and one about trends in the periodic table. Each video is about half an hour long and comes with learning objectives, note-taking guides, and worksheets.

To access these videos, go to http://www.gpb.org/public/education/classroom/chemistry/index.jsp?pcode=unit4

3. Periodic Table Concept Map Worksheet
This worksheet from the Royal Society of Chemistry includes a concept map on which students are asked to provide the links between pre-existing nodes, all of which relate to the periodic table.

4. Hands-on Minds-on Periodic Table
This is a series of activities developed to correspond to the California state standards. The goal of the activities is to help students understand the organization of the periodic table and the reactivities of the elements on the table. There are activities that focus on atoms and molecules, the organization of the periodic table, bonding, most of which involve physical model construction.

This interactive activity is found at http://www.csupomona.edu/~ceemast/science/
periodic_table/periodic_table_high_school.pdf

5. Looking for Patterns Activity
According to the Georgia Department of Education, this unit “takes an inquiry approach to understanding the patterns of properties that exist among the elements. These patterns in properties are then linked to the wave-mechanics concept of atomic structure and the quantum atom.” Several activities are presented to help students understand these concepts.