Download Graphing Trends

DRAFT 01/05
PERIODICITY
Teacher Resource
Graphing Trends
Part I: Summary of Periodic Trends
In your groups, share the graphs of physical properties that you created. Based on the trends you see
in these graphs, complete the following table together.
SUMMARY OF PERIODIC TRENDS
Trend From Left to
Property
Definition
Trend Down a Group
Right Across a Period
The distance between
nuclei of two bonded
Decreases
Increases
Atomic Radius
atoms.
The energy required
to remove a mole of
Increases
Decreases
First Ionization Energy
electrons from gaseous atoms.
The number of electrons in the outermost
Number of Valence
Increases
Constant
energy level of an
Electrons
atom.
The temperature at
which a solid turns
Decreases
Increases
Melting Point
into a liquid.
The ability of a
Decreases
Increases
Thermal Conductivity substance to conduct
heat.
Part II: Explaining Periodic Trends
Use the trends discovered in the graphs to answer the following questions.
The easier it is to lose an electron the smaller the amount of energy needed to remove it
(smaller ionization energy).
2. What happens to the amount of positive charge in the nucleus as you go from left to right across
a period?
The amount of positive charge increases as the number of protons increases from left to
right across a period.
a) How would this account for the trend you discovered in atomic radius?
Electrons are held more tightly and are pulled in closer by the nucleus as the number of
protons increases.
CHEMISTRY • PERIODICITY
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DRAFT 01/05
PERIODICITY
b) How would this account for the trend you discovered in first ionization energy?
Electrons are held more tightly by the nucleus, making it harder to lose them.
3. What is different about the number of energy levels of electrons as you go down a group?
The number of energy levels increases as you go down a group.
a) How would this account for the trend you discovered in atomic radius?
More energy levels of electrons take up more space, and the valence electrons cannot be
held as tightly by the nucleus since they are farther away.
b) How would this account for the trend you discovered in first ionization energy?
The electrons are not held as tightly by the nucleus, and can therefore be lost more easily. It takes less energy to remove them.
4. What is the relationship between the group and the number of valence electrons?
The group number is equal to the valence electrons.
5. Which properties from the Summary of Periodic Trends table describe metallic character?
Melting point and thermal conductivity
a) In general, what happens to the metallic character that elements have as you go from left to
right across a period?
Metallic character decreases.
b) In general, what happens to the metallic character that elements have as you go down a
group?
Metallic character increases.
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CHEMISTRY • PERIODICITY
Y • © 2005 MCPS SCIENCE