Transcript 4_1 Octet Rule and Ions

Chapter 4
Compounds and Their Bonds
4.1
Octet Rule and Ions
Copyright © 2009 by Pearson Education, Inc.
1
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
Ne
Ar
Kr
2
2, 8
2, 8, 8
2, 8, 14, 8
valence electrons
2
8
8
8
2
Ionic and Covalent Bonds
Atoms that are not noble
gases form octets
• to become more
stable.
• by losing, gaining, or
sharing valence
electrons.
• by forming ionic bonds
or covalent bonds.
3
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
ion 1+
Group 2A metals
ion 2+
Group 3A metals
ion 3+
Copyright © 2009 by Pearson Education, Inc.
4
Formation of a Sodium Ion, Na+
5
Charge of Sodium Ion, Na+
With the loss of its valence electron,
the sodium ion has a 1+ charge.
Na atom
11p+
11e0
Na+ ion
11p+
10e1+
2, 8
Copyright © 2009 by Pearson Education, Inc.
6
Formation of Mg2+
Magnesium achieves an octet by losing its two
valence electrons.
7
Charge of Magnesium Ion, Mg2+
With the loss of two valence
electrons, magnesium forms a
positive ion with a 2+ charge.
Mg atom
12p+
12e0
Mg2+ ion
12p+
10e2+
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8
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) Al3+.
2) Al3-.
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) Al3+.
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Formation of Negative Ions
In ionic compounds, nonmetals in Groups 5A (15),
6A (16) and 7A (17)
• achieve an octet arrangement by gaining
•
electrons.
form negatively charged ions with 3-, 2-, or 1charges.
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Formation of a Chloride, ClChlorine achieves an octet by adding an electron to
its valence electrons.
12
Charge of a Chloride Ion, ClBy gaining 1 electron, the chloride ion
has a 1- charge.
Chlorine atom, Cl Chloride ion, Cl –
17p+
17p+
17e18e0
1–
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13
Ionic Charge from Group Numbers
• The charge of a positive ion is equal to its Group
number.
Group 1A(1) = 1+
Group 2A(2) = 2+
Group 3A(3) = 3+
• The charge of a negative ion is obtained by subtracting
8 or 18 from its Group number.
Group 6A(16) =
6 - 8 = 2or 16 - 18 = 2-
14
Some Ionic Charges
15
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-.
17