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Chapter 3 Electronic Structure and Periodic Law
3.6 Property Trends within the Periodic Table
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
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Electron-Dot Symbols
An electron-dot symbol• shows the valence electrons
around the symbol of the element.
• for Mg has two valence electrons as single dots on the sides of the symbol Mg.
. . ·Mg · or Mg · or ·Mg or ·Mg
·Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
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Writing Electron-Dot Symbols
Electron-dot symbols for• groups 1A(1) to 4A(14) use single dots.
· · Na · · Mg · · Al · · C ·
·
• groups 5A(15) to 7A(17) use pairs and single dots. · · · ·
· P · : O · · ·
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Groups and Electron-Dot Symbols
In a group, all the electron-dot symbols have thesame number of valence electrons (dots).
Example: Atoms of elements in Group 2A(2) each have 2 valence electrons.
· Be ·
· Mg ·
· Ca ·
· Sr ·
· Ba ·
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A. X is the electron-dot symbol for
1) Na 2) K 3) Al
B. X
is the electron-dot symbol of
1) B 2) N 3) P
Learning Check
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A. X is the electron-dot symbol for
1) Na 2) K
B. X
is the electron-dot symbol of
2) N 3) P
Solution
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Atomic Size
Atomic size is described using the atomic radius; the distance from the nucleus to the valence electrons.
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
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Atomic Radius Within A Group
Atomic radius increases going down each group of representative elements.
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
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Atomic Radius Across a Period
Going across a period left to right, • an increase in number of protons increases attraction for
valence electrons.• atomic radius decreases.
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
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Learning Check
Select the element in each pair with the larger atomic
radius.
A. Li or K
B. K or Br
C. P or Cl
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Solution
Select the element in each pair with the larger atomic
radius.
A. K
B. K
C. P
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Ionization Energy
Ionization energy is the energy it takes to remove a valence electron.
Na(g) + Energy (ionization) Na+(g) + e-
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Ionization Energy In a Group
Going up a group ofrepresentative elements,• the distance decreases
between nucleus and valence electrons.
• the ionization energy increases.
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
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Ionization Energy
• Metals have lower ionization energies.
• Nonmetals have higher ionization energies.
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
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Learning Check
Select the element in each pair with the higher ionization
energy.
A. Li or K
B. K or Br
C. P or Cl
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Solution
Select the element in each pair with the higher ionization
energy.
A. Li
B. Br
C. Cl