Transcript Chemical Bonds
Chapter 4 Compounds and Their Bonds
4.1 Octet Rule and Ions
Copyright © 2005 by Pearson Education, Inc.
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Learning Goals
Using the octet rule, write the symbols of the simple ions for the representative elements. Using charge balance, write the correct formula for an ionic compound. Given the formula of an ionic compound, write the correct name; given the name of an ionic compound, write the correct formula. Write the name and formula of a compound containing a polyatomic ion. Given the formula of a covalent compound, write its correct name; given the name of a covalent compound, write its formula. Use electronegativity to determine the polarity of a bond. Predict the three-dimensional structure of a molecule and classify it as polar or nonpolar.
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Octet Rule
• • An
octet
is
8 valence electrons
.
is associated with the stability of the noble gases.
He is stable with 2 valence electrons (duet).
He
2
Ne 2,
8
Ar 2, 8,
8
Kr 2, 8, 14,
8 valence electrons 2 8 8 8 3
Ionic and Covalent Bonds
• • • Atoms form
octets
to become more stable. by
losing, gaining, or sharing
valence electrons.
by forming ionic bonds or covalent bonds.
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Metals Form Positive Ions
• • •
Metals
form positive ions by a loss of their valence electrons.
with the electron configuration of the nearest noble gas.
that have fewer electrons than protons. Group 1A metals Group 2A metals Group 3A metals ion 1+ ion 2+ ion 3+ Copyright © 2005 by Pearson Education, Inc.
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Formation of a Sodium Ion, Na
+
Sodium achieves an octet by losing its one valence electron.
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Charge of Sodium Ion, Na
+
With the loss of its valence electron, the sodium ion has a +1 charge. Sodium atom Sodium ion 11p + 11p + 11e 10e 0 1+ 2, 8 Copyright © 2005 by Pearson Education, Inc.
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Formation of Mg
2+
Magnesium achieves an octet by losing its two valence electrons.
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Charge of Magnesium Ion Mg
2+
With the loss of two valence Electrons, magnesium forms a positive ion with a +2 charge.
Mg atom Mg 2+ ion
12p 12e + 12p + 10e 0 2+ Copyright © 2005 by Pearson Education, Inc.
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Learning Check
A. The number of valence electrons in aluminum is 1) 1e .
2) 2e .
3) 3e .
B. The change in electrons for octet requires a 1) loss of 3e .
2) gain of 3e .
3) a gain of 5e .
C. The ionic charge of aluminum is 1) 3-.
2) 5-.
3) 3 + . D. The symbol for the aluminum ion is 1) Al 3+ .
2) Al 3 .
3) Al + .
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Solution
A. The number of valence electrons in aluminum is 3) 3 e .
B. The change in electrons for octet requires a 1) loss of 3e .
C. The ionic charge of aluminum is 3) 3 + . D. The symbol for the aluminum ion is 1) Al 3+ .
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Formation of Negative Ions
In ionic compounds,
nonmetals
• • • achieve an octet arrangement.
gain electrons
.
form negatively charged ions with 3-, 2-, or 1 charges.
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Formation of a Chloride, Cl
-
Chlorine achieves an octet by adding an electron to its valence electrons.
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Charge of a Chloride Ion, Cl
-
By gaining one electron, the chloride ion has a -1 charge.
Chlorine atom Chloride ion
17p + 17p + 17e 0 18e 1 – Copyright © 2005 by Pearson Education, Inc.
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Ionic Charge from Group Numbers
• The charge of a positive ion is equal to its Group number.
Group
1A(1)
=
1+
Group
2A(2)
Group
3A(3)
= =
2+ 3+
• The charge of a negative ion is obtained by subtracting 8 or 18 from its Group number. Group
6A(16)
=
6
- 8 =
2-
or
16
- 18 =
2 15
Some Ionic Charges
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Learning Check
A. The number of valence electrons in sulfur is 1) 4e .
2) 6e .
3) 8e .
B. The change in electrons for octet requires a 1) loss of 2e .
2) gain of 2e . 3) a gain of 4e .
C. The ionic charge of sulfur is 1) 2+.
2) 2-.
3) 4-.
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Solution
A. The number of valence electrons in sulfur is 2) 6e .
B. The change in electrons for octet requires a 2) gain of 2e .
C. The ionic charge of sulfur is 2) 2-.
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