Chapter 3 Atoms and Elements 3.7 Trends in Periodic Properties 1 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition

Chapter 3

Atoms and Elements

3.7Trends in Periodic Properties

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Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Group Number and Valence Electrons

For representative elements in Groups 1A–8A, chemical properties are due to the number of valence electrons.

Valence electrons are the number of electrons in the outermost energy level.

The group number gives the number of valence electrons for the representative elements.

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Group Number and Valence Electrons

Group Number # Valence Electrons 1A 1 2A 2 3A 3 4A 4 5A 5 6A 6 7A 7 8A 8

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Electron-Dot Symbols

Electron-dot symbols

• are also known as Lewis structures

• represent the valence electrons as dots placed on sides of symbol

For example, Al = 2,8,3

Three valence electrons are represented as dots:

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Al


Electron-Dot Symbol for Mg

Possible electron-dot symbols for magnesium, with the electron arrangement of 2,8,2,

• include 2 valence electrons, represented as dots

• can be drawn in more than one way

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Mg Mg

Mg Mg

Mg

Mg


Electron-Dot Symbol for Mg6


Electron-Dot Symbols for Selected Elements7


Learning Check

Write the electron-dot symbol for each of the following elements: Cl, C, N.

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Solution

Write the electron-dot symbol for each of the following elements:

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C NCl


Atomic Size

Atomic size• is determined by the atom’s atomic radius, the distance

between nucleus and outermost electrons

• increases for representative elements from top to bottom of the periodic table

• decreases within a period due to increased number of protons in nucleus

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Atomic Size11


Atomic Size12


Ionization Energy

Ionization energy

• is the energy required to remove one of the outermost electrons from an atom

Na(g) + energy (ionization) Na+(g) + e−

• decreases down a group, increases across a period from left to right

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Ionization Energy14


Metallic Character

An element with metallic character is one that loses electrons easily.

Metallic character

• is more prevalent in metals on left side of periodic table

• is less for nonmetals on right side of periodic table that do not lose electrons easily

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Metallic Character16


Summary of Trends in Periodic Table17


Learning Check

Given the following elements: C N Cl

Which is the largest atom?

Which has the highest ionization energy?

Which belongs to Group 5A?

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Solution

Given the following elements: C N Cl

Which is the largest atom? C

Which has the highest ionization energy? Cl

Which belongs to Group 5A? N

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Documents

Chapter 3 Atoms and Elements 3.7 Trends in Periodic Properties 1 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition