Download It`s Trendy! The periodic table not only provides us with atomic

It’s Trendy!
decreases
increases
The periodic table not only provides us with atomic numbers of elements and masses of elements, but it also
provides us with a tool to determine general trends in chemical and physical properties.
1. Atomic Radius—the atomic radius is defined to be the
decreases
distance from the nucleus to the outer energy level where
the outermost electrons are. The atomic radius decreases
Smallest
as you move from left to right across a period and increases
atom
as you move from top to bottom in a family. But why? For a
period, you are in the same energy level which itself
describes the size of the electron cloud (the area where the
electrons
increase
increases
Largest atom
are most
probably
Largest
located), so based on this elements should have the same
value
radius in the same period. But as you move across the
period, the total positive charge in the nucleus increases
thereby increasing the total force attracting the electrons in
the outer energy level thereby making the cloud contract.
As you go down a family it is much easier to understand
Smallest value
the trend. As you go down a family the energy level
increases thereby increasing the radius of the cloud so the atomic radius increases.
2. Ionization Energy—this is defined as the amount of energy needed to remove an electron from the outer
energy level of an atom. Here the trend is to increase from left to right across a period and to decrease
from top to bottom in a family. Why? As previously stated, the size decreases as you move from left to
right as the total positive charge increases. By the inverse square law (F=kQ1Q2/r2) this means the force
attracting the electron increases as size decreases and as the positive charge increases. As you move
from top to bottom again using the inverse square law, you get farther from nucleus thus reducing the
attractive force on the electron.
decreases
3. Electron Affinity—this is defined as the amount of energy required to add an electron. For all but one
column this value is either negative or zero. The 2nd family is
the only one that is consistently positive. Here the negative
increases
energy implies that energy is released rather than required
when an electron is added. The trends here are exactly the
Most
same as for ionization energy. From left to right the energy
Negative
is more negative—high affinity--and from top to bottom it is
Value
less negative—lower affinity. The reasoning is very similar to
those for ionization energy.
Least Negative Value
or Most Positive Value
increases
decreases
4. Electro negativity—this
is defined as the
attraction of one atom in a molecule for the shared electrons. The trend
is exactly the same as for electron affinity and ionization energy. The
reasoning is also the same. Fluorine is set at the highest at 4.0 and all
other atoms are lower than this.
5. Reactivity—this is defined as how readily an atom reacts. For metals
this is based on ionization energy where the most reactive metals are
Smallest value
those with the lowest ionization energies. For nonmetals this is based
on electron affinity where the most negative electron affinity is the most reactive. This has to do with the
fact that metals form positive ions (lose electrons) and nonmetals for negative ions (gains electrons).
Largest
value
Materials
 graph paper
 activity series for metals and nonmetals (found in any chemistry text or on the internet)
Description
Note: This activity is intended to be an activity used before the students are taught the trends. It is to be used
to have the students recognize the repeating patterns in the graphs. After the completion of the activity, the
explanations of the trends may be addressed depending on the level of the students.
Before you begin to plot data points, mark the elements on a periodic table that you will be graphing. Make
sure to keep track of elements within the same group and within the same period. A color coding system or an
outlining system may be helpful. Doing this will help you to answer the questions that follow.
Instructions: Read Very Carefully. Each graph should take up as much of the graph paper as possible. The
dots should be connected by a line using a ruler. Be sure to title and label each graph. Intervals for each
graph have been given in the paragraph below. Your job is to decide the layout of your graph so it takes up
most of the paper.
Each property should be graphed on a separate sheet of graph paper. For the following data, plot the
atomic number on the x-axis and the property on the y-axis. The intervals will be “1” . Atomic Radius:
y axis range, 0-270; each interval is “10”. 1st Ionization Energy: y axis range, 0-2500; each interval is
“100”. Electron Affinity: y axis range, -400 to 300; each interval is “20”. Electronegativity: y axis
range, 0 – 5; each interval is “1”
Element
Atomic
Number
Atomic Radius
(pm)
1st Ionization
Energy (kJ/mol)
Electron Affinity
(kJ/mol)
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
53
31
167
112
87
67
56
48
42
38
190
145
118
111
98
88
79
71
1312
2372
520
899
801
1086
1402
1314
1681
2081
496
738
578
787
1012
1000
1251
1521
-73
0
-60
240
-27
-122
0
-141
-328
0
-53
230
-44
-134
-72
-200
-349
0
Electro
negativity
(Pauling Units)
2.1
NA
1.0
1.5
2.0
2.5
3.0
3.5
4.0
NA
0.9
1.2
1.5
1.8
2.1
2.5
3.0
NA
Name _____________________________________________ Date ______ Block _______
Analysis
1. Based on your graphs, what is the trend in atomic radius across a period? down a family?
2. Based on your graphs, what is the trend in ionization energy across a period? down a family?
3. Based on your graphs, what is the trend in electron affinity across a period? down a family?
4. Based on your graphs, what is the trend in electro negativity across a period? down a family?
5. Using an activity series (found in your text book or the internet), what can you deduce about the
relationship between ionization energy and reactivity of metals?
6. Using an activity series, what can you deduce about the relationship between electron affinity and reactivity
of nonmetals?
7. Explain in 3-4 paragraphs the organization and usefulness of the modern periodic table based on what you
have learned in class and what you have learned from this activity. (Paragraphs imply complete
sentences.)