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 Mg
Manganese Mn
Neon
Ne
Nickel
Ni
Nitrogen N
Oxygen
O
Phosphorus P
Potassium K
Rubidium Rb
Scandium Sc
Selenium Se
Silicon
Si
Sodium
Na
Strontium Sr
Sulfur
S
Titanium Ti
Vanadium V
Zinc
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.
Make a graph of atomic radius v. atomic number using the above data. Choose an appropriate scale.
2.
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?
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