Name: ______________________________________________________
Period: _______
Objective: SWBAT predict the atomic radius of elements by graphing the atomic radius vs. atomic number.
1. become familiar with the organization of the periodic table
2. study a periodic property
3. make predictions based on periodic properties
Discussion:
The periodic law states that many properties of the elements are periodic functions of their atomic numbers. A periodic
function is one which goes through cycles, with maximum and minimum values at regular intervals. The atomic radius,
melting point, and boiling point are periodic properties of the elements. The periodic table arranges the elements in
order of increasing atomic number in such a way that the periodic nature of properties is made clear. This is done by
placing in the same vertical column of the table those elements which appear at corresponding positions in the cycle of
properties. For example, since the atomic radii of Li, Na, K, Rb, and Cs appear at maxima in the cycles for atomic radii as
a function of atomic number, we would expect that these elements would be in the same column in the periodic table.
These elements belong to a family, or Group, and have many other properties which would also indicate that they
should be classified together. In general, properties of the elements in a Group tend to change gradually as one goes
from the lightest to the heaviest atom in the Group. Within the framework of the periodic table properties vary
according to a pattern as you move across the table in a cycle, or period, or up and down one of the Groups. If the
pattern for the variation is known, it is often possible to predict a property of one element from the properties of
elements which lie nearest that element in the table. Depending on the position of the element in the table, the best
prediction will either be based on elements in the same row or eon elements in the same column, as the element for
which the prediction is to be made.
In this experiment you will make some graphs of periodic properties against atomic number in order to discover the
patterns the properties follow. You will then use those patterns to predict some properties of elements.
Procedure:
1. Using the data in Table 1, plot the atomic radius of each element on the y-axis against its atomic number on the
x-axis. Make the x-axis on the long side of the paper and choose the scales so that all the data will fit on the
sheet. Connect each two consecutive points with a straight line. Label each peak with the symbol of the
element.
2. For Mg and Fe; skip their plot point when plotting the points. When connecting the points, connect Na to Al and
Mn to Co with a straight line.
Thornburg 2014
Name: ______________________________________________________
Table 1 Atomic Radii of Elements in nm
Period: _______
Element
Atomic
Number
Atomic Radius
Element
Atomic
Number
Atomic Radius
H
He
Li
Be
B
C
N
O
F
Ne
Na
Mg
Al
Si
P
S
Cl
Ar
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
0.037
0.050
0.152
0.111
0.088
0.077
0.070
0.066
0.064
0.070
0.188
unknown
0.143
0.117
0.110
0.104
0.099
0.094
K
Ca
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
Ga
Ge
As
Se
Br
Kr
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
0.231
0.197
0.160
0.146
0.131
0.125
0.129
unknown
0.125
0.124
0.128
0.133
0.122
0.122
0.121
0.117
0.114
0.109
Questions:
1. Describe any regularities that are present in the graph of atomic radius versus atomic number.
2. Which elements occupy the “peaks” in the cycles?
3. Would you expect the elements at the “peaks” which have large atomic radii to have large or small ionization
energy (the energy required to lose valence electrons)? Explain your answer
4. Which elements occupy the “valleys” in the cycles?
5. Would you expect the elements at the “valleys” which have small atomic radii to have large or small ionization
energy? Explain your answer
6. How many elements separate each peak? How does this correlate to the periods on the periodic table?
7. In Table 1 the atomic radii of Mg and Fe blank intentionally. The part of the cycle from Li (3) to B (5) is repeated
in the part of the cycle from Na (11) to Al (13). One would then expect that the radius of Mg would have a value
that would maintain the pattern observed between Li and B. On that basis, predict the radius of the Mg atom
from the graph
8. As part of the last cycle on the graph, which starts at K (19), we have the first series of transition metals. By
assuming that the Fe (26) atom would maintain the pattern set by atoms near it in atomic number, predict the
radius of the Fe atom from the graph.
9. Using your periodic table and the pattern on the graph would you predict Rb to have a smaller or larger atomic
radius than K? Explain why.
Thornburg 2014