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Performance 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
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%5Cp
eriodic_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%5Cp
eriodic_table.html#)
Performance 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.
To learn more about this, go to
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.
To learn more about atomic radii and other periodic properties, go to
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_tab
le.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.
To learn more about chemistry misconceptions, go to
http://educ.queensu.ca/~science/main/concept/chem/c07/C07CDTL1.htm.
Performance 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
Students should use the following periodic table to answer these questions.
Figure 6. Periodic table of elements
(From http://www.bpc.edu/mathscience/chemistry/images/periodic_table_of_elements.jpg)
1. What is the symbol for the element in period 3 and group 5A?
a. As
b. Nb
c. Y
d. P
2. What property is the element sulfur (S) most likely to have?
a. conduct heat and electricity
b. be shiny
c. have a dull appearance
d. melt at a high temperature
3. In which of the following pairs are both elements in the same group?
a. Br and I
b. O and I
c. F and Ne
d. He and H
4. In which of the following pairs are both elements in the same period?
a. Br and I
b. O and I
c. F and Ne
d. He and Hf
5. The periodic table is arranged in order of increasing _________.
a. number of protons
b. number of electrons
c. atomic weight
d. mass number
6. Which of the following elements will react similarly to tellurium (Te)?
a. germanium (Ge)
b. xenon (Xe)
c. sulfur (S)
d. titanium (Ti)
7. Which of the following elements would be expected to have the largest atomic radius?
a. sulfur (S)
b. polonium (Po)
c. tellurium (Te)
d. oxygen (O)
8. Which of the following elements would be expected to have the largest atomic radius?
a. boron (B)
b. nitrogen (N)
c. neon (Ne)
d. lithium (Li)
9. Which of the following elements would be expected to have the largest ionization
energy?
a. boron (B)
b. nitrogen (N)
c. neon (Ne)
d. lithium (Li)
10. Which of the following elements would be expected to have the smallest
electronegativity?
a. chlorine (Cl)
b. astatine (At)
c. iodine (I)
d. fluorine (F)
11. Which of the following subatomic particles determines how an atom will behave in a
chemical reaction?
a. protons
b. electrons
c. neutrons
d. nucleus
12. How many valence electrons does oxygen (O) have?
a. 0
b. 6
c. 8
d. 16
Performance 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
Answers to Sample Test Questions
1. (d)
2. (c)
3. (a)
4. (c)
5. (a)
6. (c)
7. (b)
8. (d)
9. (c)
10. (b)
11. (b)
12. (b)
Performance 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 list of intervention strategies and resources 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.
This table can be found at
http://www.chemistry.org/portal/a/c/s/1/acsdisplay.html?DOC=sitetools%5Cperio
dic_table.html#
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.
To download this worksheet, go to
http://www.chemsoc.org/pdf/LearnNet/miscon2/The_periodic_table.pdf
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_sch
ool.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.
To access these activities go to ,
http://public.doe.k12.ga.us/DMGetDocument.aspx/Chemistry-BlockFinding%20Patterns-Framework%202-2607.pdf?p=6CC6799F8C1371F6B6A573BA546CF1D20522D9E8BC0D8E5DB48CE
EC58FD59386&Type=D