DRAFT DOCUMENT
LAB 12
PERIODIC TRENDS
In the 1800’s Mendeleev used the chemical and physical properties of the elements to
develop an arrangement of the elements that today we call the periodic table. In this lab
activity you will investigate how three properties of the elements – atomic radius,
ionization energy, and electronegativity – vary according to the atomic number of the
elements. You will be making a 3-dimensional model of these properties for some of the
representative elements and use it to describe and explain the trends in these properties.
OBJECTIVES
When you have completed this activity, you should be able to
1. Use a model to describe the trends in several physical properties of the elements.
2. Relate these trends to the electron configuration of the elements.
MATERIALS
96-Well microplate
Ruler
Calculator
Forceps
Scissors
Straws, 3 colors
Ruler
Periodic table
PROCEDURE
1. Each pair of students will prepare a 3-dimensional model for at least one of the
properties of the elements. You will then share your results will students in other
groups. Your group has been assigned to make a model for the property
______________________________. Use masking tape to label the well plate
with this property.
2. In order to make the 3-D model you need to cut the straws to scale so their heights
represent the relative values for each element. On the Data Table provided,
convert the values for your assigned property to a scale in centimeters by using
the conversion factors given below. Round your answers to the nearest tenth of a
centimeter. An example is given for each property.
Property
Atomic radius
Ionization Energy
Electronegativity
Conversion
Factor
Example
(For Hydrogen)
32 pm x 1cm = 1.07 cm ( 1.1 cm)
1 cm =30 pm
30 pm
1312 kJ x 1cm = 3.28 cm ( 3.3 cm)
1 cm = 400 kJ
400 kJ
2.2 units x 1cm
= 2.75 cm ( 2.8 cm )
1 cm= 0.8 unit
0.8 unit
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LAB 12
3. Use the diagram of the well plate provided below to plan the placement of the
elements. Your well plate should be oriented to correlate with the elements of the
periodic table. Row 1 represents the first period, with well H1 as Hydrogen and
well A1 as Helium. Row 2 represents the second period with well H2 as Lithium
and well A2 as Neon. Rows 3 and 4 contain the elements in periods 3 and 4,
omitting the transition elements.
Write the symbols for the elements in the circles.
4.
Select colored straws to represent your property.
5. Carefully measure and cut a piece of straw for each element. Following the
diagram you completed in Procedure 3, insert each piece into the appropriate well
of the microplate.
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LAB 12
ANALYSIS
1.
Examine your tray and those of other student groups. How do the properties
change as you look from top to bottom within a group or family?
Atomic radius
Ionization energy
Electronegativity
2. As you look from left to right across the periodic table, how do the properties
change?
Atomic radius
Ionization energy
Electronegativity
3. Write the electron configuration for the following alkali metals (Group 1).
Li
Na
K
In what way are the electron configurations for group 1 similar?
How do the electron configurations differ as you move down group 1?
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LAB 12
4. Write the electron configuration for the elements in period 2, from Li to Ne.
Li
Be
B
C
N
O
F
Ne
What do all the electron configurations above have in common?
How do these electron configurations differ? How do the number of protons differ?
5. In terms of electron configuration, explain the trend in atomic radius.
Down a group
Across the period from left to right
6. In terms of electron configuration, explain the trend in ionization energy.
Down a group
Across the period from left to right
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LAB 12
7. In terms of electron configuration, explain the trend in electronegativity.
Down a group
Across the period from left to right
8.
Look at your model again. Why do you think we say that the properties of the
elements are “periodic”?
9. On the diagram of the periodic table below draw and label arrows that show the
direction in which the three properties ( atomic radius, ionization energy,
electronegativity) increase.
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LAB 12
10. Write a paragraph explaining why atomic radius, electronegativity, and ionization
energy show periodic trends. The following rubric will be used to assess your
understanding.
Scoring tool:
Score
Students use patterns illustrated in model and electron
configuration of the elements to explain clearly why the
three properties are periodic. Specific examples are
given for each trend.
Students use patterns illustrated in model and explain
in general terms how the electron configuration of the
elements cause the properties to be periodic.
3
Students can describe the patterns illustrated by the
models and relate the patterns to electron configuration
with some errors.
2
Students can describe the patterns illustrated by the
models but do not explain in terms of electron
configuration.
Students cannot describe the patterns illustrated by the
models
11.
4
1
0
Some of the elements show exceptions to the trends. Look at your model and
select an element that seems to have an unusual value for one of these properties.
Try to explain why this happens by writing the electron configuration for this
element and looking for a definite change from the element before it.
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LAB 12
PROPERTIES OF REPRESENTATIVE ELEMENTS
Element Atomic Atomic
Straw
Ionization Straw Electronegativity Straw
number radius length(cm) Energy
(pm)
(kJ/mol) Length
length
(cm)
(cm)
H
He
Li
Be
B
C
N
O
F
Ne
Na
Mg
Al
Si
P
S
Cl
Ar
K
Ca
Ga
Ge
As
Se
Br
Kr
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
31
32
33
34
35
36
32
50
155
112
98
91
92
73
72
71
190
160
143
132
128
127
99
98
235
197
141
137
139
140
114
112
1312
2372
520
900
801
1086
1402
1314
1681
2081
496
738
578
786
1012
1000
1251
1520
419
590
579
762
944
941
1140
1351
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2.2
1.0
1.6
2.0
2.5
3.0
3.5
4.0
0.9
1.3
1.6
1.9
2.2
2.6
3.2
0.8
1.0
1.4
2.0
2.2
2.5
3.0
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DRAFT DOCUMENT
LAB 12
PRE-LAB: PERIODIC TRENDS
1. Which groups of the periodic table contain the “representative elements”?
Why do you think these elements are called “representative”?
2. What is a periodic trend?
3. Consult a chemistry textbook to find the definitions for the following properties,
then restate the definition in your own words.
Atomic radius
Ionization energy
Electronegativity
4. Read the procedure for this activity. What is the purpose for including drinking
straws in the Materials list?
5. Follow the directions in Procedure 2 to calculate the straw length needed to
represent
The atomic radius of oxygen
The ionization energy of neon
The electronegativity of arsenic
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