Periodic Trends: Graphing Atomic Radii
The periodic table is a wonderful source of information about all the elements
scientists have discovered. In this activity, you will investigate the relationship among
elements’ atomic numbers, radii, and positions in the periodic table.
The radii for elements with atomic numbers 3-38 are given in table 1. The radii are
so small that a very small metric unit called a picometer is used. A picometer (pm) is one
trillionth of a meter (1 x 10-12 m).
In this activity, you will graph the atomic radii of the elements with atomic numbers
3-38 and examine the graph for repeating patterns.
Table 1: Atomic Radii
Name and symbol
Atomic
number
Aluminum
Al
13
Argon
Ar
18
Arsenic
As
33
Beryllium
Be
4
Boron
B
5
Bromine
Br
35
Calcium
Ca
20
Carbon
C
6
Chlorine
Cl
17
Chromium
Cr
24
Cobalt
Co
27
Copper
Cu
29
Fluorine
F
9
Gallium
Ga
31
Germanium
Ge
32
Iron
Fe
26
Krypton
Kr
36
Lithium
Li
3
Atomic radius
(picometers)
143
191
121
112
85
117
197
77
91
128
125
128
69
134
123
126
201
156
Name and symbol
Magnesium
Manganese
Neon
Nickel
Nitrogen
Oxygen
Phosphorus
Potassium
Rubidium
Scandium
Selenium
Silicon
Sodium
Strontium
Sulfur
Titanium
Vanadium
Zinc
Mg
Mn
Ne
Ni
N
O
P
K
Rb
Sc
Se
Si
Na
Sr
S
Ti
V
Zn
Atomic
number
12
25
10
28
7
8
15
19
37
21
34
14
11
38
16
22
23
30
Atomic radius
(picometer)
160
127
131
124
71
60
109
231
248
162
119
118
186
215
103
147
134
134
Procedure
1. On the graph paper, label the horizontal axis with the numbers 0-38 to represent the
atomic numbers of the elements you will be plotting.
2. Label the vertical axis by ten with numbers 0- 280. These numbers represent the atomic
radii.
3. Plot the atomic radius for each of the elements with atomic numbers 3-38. Label each
point with the corresponding element symbol. When you have finished plotting points,
connect the plotted data to create a line graph.
Source: Glencoe/McGraw-Hill
pp. 21-22
Periodic Trends: Graphing Atomic Radii
Source: Glencoe/McGraw-Hill
pp. 21-22
Questions and Conclusions:
1. Look at the shape of your graph. What patterns do you observe? _________________
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2. What family is represented by the high peaks on your graph? ____________________
3. What family is represented by the low peaks on your graph? _____________________
4. What family is represented by the smaller peaks just before the high peaks in your
graph?_______________________________________________________________
5. What do you notice about the radii of the elements at the high peaks as you move from
left to right on your graph? Look at your periodic table and find the element that
represents each high peak. Where does each high peak begin in the periodic table?
____________________________________________________________________
____________________________________________________________________
6. What happens to the radii of the elements between two highest peaks? What does each
of these groups of elements represent?
____________________________________________________________________
____________________________________________________________________
____________________________________________________________________
7. How can graphs such as the one you made help to predict the properties of elements that
have not been discovered yet? _____________________________________________
____________________________________________________________________
____________________________________________________________________
____________________________________________________________________
____________________________________________________________________
8. How do the radii of metals in each period compare with the radii of nonmetals in that
period?
____________________________________________________________________
____________________________________________________________________
Source: Glencoe/McGraw-Hill
pp. 21-22