TRENDS IN THE PERIODIC TABLE: A GRAPHICAL ANALYSIS
The purpose of this assignment is to demonstrate that there is regular variation in the
properties of the elements when the elements are arranged in order of increasing atomic
number. It also illustrates that predictions can be made based on this regular variation.
Part One: Atomic Radii of the Elements
The atomic radius of an atom is the distance from the center of the nucleus to the valence
level of electrons. To obtain this measurement, the radius must be determined for a
nonbonded atom in the gaseous state. The table on the second page lists data for the first
36 elements.
1. Use pen for axes and labels and pencil for data points and lines.
2. Prepare a graph with the atomic number on the horizontal axis and the atomic
radius on the vertical axis. Choose your scales so that the graph occupies the
majority of the graph paper and all of the data can be plotted. Using a ruler,
connect the points.
3. Divide the horizontal axis into 36 intervals using as much of the axis as possible.
4. Join consecutive points with straight solid lines. If the data for an element is
missing, extrapolate using a broken straight line to join the points for adjacent
elements.
5. Circle the points corresponding to the peaks on the graph. Write the symbol for
the elements at each peak.
6. Put a square around the points corresponding to the lowest points (troughs) on the
graph. Write the symbol for the element at each trough.
QUESTIONS:
Part One:
1. a) What is the group name for the elements found at the peaks of your graph?
b) What is the group name for the elements found at the troughs of your graph?
2. a) What is the general trend in the size of atomic radii as the atomic number
increases within a group?
b) Explain the cause of this trend by referring to the structure of the atom.
3. a) What is the general trend in the atomic radii as the atomic number increases
across a period?
b) Explain the cause of this trend by referring to the structure of the atom.
4. Using the trends apparent in your graph, extrapolate (predict) the value of the
atomic radius for these elements: a) fluorine b) cobalt
5. Would you expect the atomic radius for rubidium (element 37) to be larger or
smaller than the atomic radius for element 36? Explain your reasoning.
Part Two: First Ionization Energies for the Elements
Using the same method as in Part One, plot a graph of first ionization energy versus
atomic number.
QUESTIONS:
Part Two:
1. What is meant by “first ionization energy”?
2. a) What group of elements corresponds to the peaks of ionization energy on your
graph?
b)
Which group of elements occupies the troughs on your graph of ionization
energy?
3. a) Describe the trend in the first ionization energies as the atomic number increases
within a group of elements?
b)
Explain the cause of this trend by referring to the structure of the atom.
4. a) Describe the trend in the first ionization energies as the atomic number increases
across a period or row of elements?
b)
Explain the cause of this trend by referring to the structure of the atom.
5. Using the trends apparent in your graph, extrapolate (predict) the value of the first
ionization energy for these elements: a) fluorine
b) cobalt
6. Predict a value for the ionization energy for element 37 based on the trends in
visible in your graph.
7. a) An anomaly is a piece of data that does not fit the general trend. Identify one
anomaly to the trends you identified in the first ionization energy data. b) Create a
hypothesis (an explanation) that may explain this anomaly.
Properties of the Elements
Element
Al
Ar
As
B
Be
Br
C
Ca
Cl
Co
Cr
Cu
F
Fe
Ga
Ge
H
He
K
Kr
Li
Mg
Mn
N
Na
Ne
Ni
O
P
Rb
S
Sc
Se
Si
Ti
V
Zn
Atomic
Number
13
18
33
5
4
35
6
20
17
27
24
29
9
26
31
32
1
2
19
36
3
12
25
7
11
10
28
8
15
37
16
21
34
14
22
23
30
Atomic Radius
(pm)
118
71
114
87
112
94
67
194
79
166
145
156
136
125
53
31
243
88
167
145
161
56
190
38
149
48
98
88
184
103
111
176
171
142
First Ionization Energy
(kJ/mol)
577
1520
947
801
900
1140
1086
590
1251
653
745
759
579
762
1312
2372
419
1520
513
738
717
1402
496
2081
737
1314
1060
1000
631
941
786
658
651
906