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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.

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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.

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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