Names:______________________________________________________
Assigned on October 6, 2015
Atomic Structure and the Periodic Table Unit
Lab: Exploring Periodicity
Problem: How do we use the model of the electronic structure of the atom to understand periodic trends of the elements?
FIGURE 1
Part 1: Atomic Radii
Go to the following web address:
http://group.chem.iastate.edu/Greenbowe/secti
ons/projectfolder/flashfiles/matters/periodicTb
l2.html
When the animation starts, you will see the
picture shown in FIGURE 1. Be sure the
switch at the top of the animation is on “Atom
View.”
Section A
1. Look at the atomic sizes shown in the table and describe all the trends that you see. Be sure to think about both periods and groups!
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2. Click on an atom in the row of atoms above the periodic table and drag them to their respective location in the periodic table. After
moving the atoms into their correct positons on the computer screen, draw them and write their atomic radii to the periodic table
in FIGURE 1 above.
3. Select one of the Groups (1, 2, 16, or 17) and complete TABLE 1for the elements in your selected group. Note: Column (i) will be
used later in this activity.
TABLE 1
(a)
Element
Symbol
(b)
(c)
(d)
(e)
(f)
(g)
Atomic
Radius
Nuclear
Charge (#
of Protons)
Total # of
Electrons
Electron
Configuration
# of Core
Electrons
# of
Valence
Electrons
(h)
Energy
Level of
Valence
Electrons
(i)
Honors Chemistry | page 1
4. Work with another group that has also completed TABLE 1 and answer questions a-c below.
a) Which columns (c—h) in TABLE 1 do not explain the trend in atomic radius observed in your selected group? Explain
why not.
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b) Which columns (c—h) in TABLE 1 do explain the trend in atomic radius observed in your selected group? Explain why.
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c) Which column (c—h) in TABLE 1 best explains the trend in atomic radius observed in your selected group? Explain why
you selected that column.
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5. The atomic radius of phosphorus is 1.06 Å and of arsenic is1.25 Å. Provide and explanation why the atomic radius of arsenic is
larger than the atomic radius of phosphorus.
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6. Write a general statement that explains the trend in atomic radius that applies to any Group of the Periodic Table.
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Section B
7. Select one of the Periods (horizontal rows) and complete TABLE 2 for the elements in your selected period. Note: Column (i) will
be used later in this activity.
TABLE 2
(a)
Element
Symbol
(b)
(c)
(d)
(e)
(f)
(g)
Atomic
Radius
Nuclear
Charge (#
of Protons)
Total # of
Electrons
Electron
Configuration
# of Core
Electrons
# of
Valence
Electrons
(h)
Energy
Level of
Valence
Electrons
(i)
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8. Work with another group that has also completed TABLE 2 and answer questions a-c below.
a) Which columns (c—h) in TABLE 2 do not explain the trend in atomic radius observed in your selected period? Explain
why not.
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b) Which columns (c—h) in TABLE 2 do explain the trend in atomic radius observed in your selected period? Explain why.
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c) Which column (c—h) in TABLE 2 best explains the trend in atomic radius observed in your selected period? Explain why
you selected that column.
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9. The atomic radius of aluminum is 1.18 Å and of phosphorus is1.06 Å. Provide and explanation why the atomic radius of arsenic is
larger than the atomic radius of phosphorus.
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10. Write a general statement that explains the trend in atomic radius that applies to any Period of the Periodic Table.
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Section C
Nuclear charge is the total positive charge in the nucleus. For example, the nuclear charge for a carbon atom is 6+. The nuclear charge
is equivalent to the atomic number for an element. Effective nuclear charge (Zeff) is a term used to describe the amount of nuclear
charge experienced by a particular electron in an atom. Consider the following information for carbon:
(a)
(b)
(c)
(d)
(e)
(f)
(g)
Element
Symbol
Atomic
Radius
Nuclear
Charge (#
of Protons)
Total # of
Electrons
Electron
Configuration
# of Core
Electrons
# of
Valence
Electrons
C
0.77 Å
6+
6
1s22s22p2
2
4
(h)
Energy
Level of
Valence
Electrons
(i)
Effective
Nuclear
Charge
(Zeff)
2
4+
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If we focus on the electron configuration for carbon, we see there are 2 electrons in the first level and 4 electrons in the second level.
Electrons in the second level are further away from the nucleus. The 2 electrons in the first level (core electrons) partially shield the
valence electrons from some of the nuclear charge. As an approximation, we will assume each core electron shields the charge of one
proton from the electrons in in the valence shell.
The Zeff is calculated by subtracting the number of core electrons (CE) from the total nuclear charge (Z): Z eff = Z – CE. In the case of
carbon, Zeff = 6 – 2 = 4+.
11. Return to TABLE 1 and TABLE 2 and write Effective Nuclear Charge (Z eff) in column (i).
12. In TABLE 1 and TABLE 2, complete column (i) by determining the effective nuclear charge for each of the element listed. Show
your work below for the calculation of Zeff for any two of the elements in TABLE 1 and two elements in TABLE 2.
Get together with another group to work on the rest of the questions in this lab.
13. Is there a relationship between Zeff and the trend in atomic radius for the elements in a group? Use TABLE 1 to help you with this
determination. Explain your reasoning.
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14. Is there a relationship between Zeff and the trend in atomic radius for the elements in a period? Use TABLE 2 to help you with this
determination. Explain your reasoning.
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15. Last year, I heard a student make the following assertion to another student:
“When I look at FIGURE 1, it appears to me that as the nuclear charge increases, the size of the atom also increases.”
Cite evidence that supports and/or refutes this student’s statement.
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16. Define “ionization energy.”
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17a. Find a periodic table that contains the ionization energy values for each element. What trend in ionization energy do you see
going down a group on the periodic table?
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b. Using what you have learned in this activity, what explanation can you give for this trend as you go down a group?
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18a. Using the same periodic table with ionization energy values, what trend do you see in ionization energy going across a period on
the periodic table?
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b. Using what you have learned in this activity, what explanation can you give for this trend as you go across a period?
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19. When you look across period 2, you will notice that boron does not follow the general trend for ionization energy across a period.
Can you offer a reason for this exception? (Hint: notice that aluminum and gallium also do not follow the trend in their periods.)
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20. Define “electronegativity.”
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21a. Find a periodic table that contains the electronegativity values for each element. What trend in electronegativity do you see going
down a group on the periodic table?
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b. Using what you have learned in this activity, what explanation can you give for this trend as you go down a group?
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22a. Using the same periodic table with electronegativity values, what trend do you see in electronegativity going across a period on
the periodic table?
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b. Using what you have learned in this activity, what explanation can you give for this trend as you go across a period?
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