Transcript Chemical Bonds

Chapter 5
Compounds and Their Bonds
5.1
Octet Rule and Ions
General, Organic, and Biological Chemistry
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Octet Rule
An octet
 is 8 valence electrons
 is associated with the stability of the noble gases
 does not occur with He; He is stable with 2 valence
electrons (duet)
Valence Electrons
He 1s2
2
Ne 1s22s22p6
Ar
8
1s22s22p63s23p6
8
Kr 1s22s22p63s23p64s23d104p6
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Ionic and Covalent Bonds
Atoms form octets
 to become more stable
 by losing, gaining, or
sharing valence electrons
 by forming ionic 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(1) metals
Group 2A(2) metals
Group 3A(3) metals
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ion 1+
ion 2+
ion 3+
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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, a sodium ion has a 1+
charge.
Sodium atom
11p+
11e–
0
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Sodium ion
11p+
10e–
1+
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Formation of Magnesium Ion, Mg2+
Magnesium achieves an octet by losing its two
valence electrons.
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Charge of Magnesium Ion, Mg2+
With the loss of two valence
electrons magnesium forms a
positive ion with a 2+ charge.
Mg atom
12p+
12e–
0
Mg2+ ion
12p+
10e–
2+
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Learning Check
A. The number of valence electrons in aluminum is
1) 1e–
2) 2e–
3) 3e–
B. To acquire an octet of electrons in aluminum requires
1) a loss of 3e–
2) a 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+
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2) Al3–
3) Al+
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Solution
A. The number of valence electrons in aluminum is
3) 3 e–
B. To acquire an octet of electrons in aluminum requires
1) a 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
 achieve an octet arrangement
 gain electrons
 form negatively charged ions
with 3–, 2–, or 1– charges
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Formation of a Chloride Ion, 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
17p+
17e–
0
Chloride ion
17p+
18e–
1–
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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) = 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 = 2–
or 16 – 18 = 2–
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Some Typical Ionic Charges
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Group Number and Ionic Charge
Ions
 achieve the electron configuration of their
nearest noble gas
 of metals in Groups 1A(1), 2A(2), or 3A(13) have
positive 1+, 2+, or 3+ charge.
 Of nonmetals in Groups 5A(15), 6A(16), or 7A(17)
have negative 3–, 2–, or 1– charge.
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Groups Numbers for Some
Positive and Negative Ions
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Learning Check
A. The Group number for sulfur is
1) 4A(14)
2) 8A(18)
3) 6A(16)
B. The number of valence electrons in sulfur is
1) 4e
2) 6e
3) 8e
C. The change in electrons for an octet requires a
1) gain of 2e
2) loss of 2e
3) a gain of 4e
D. The ionic charge of sulfur is
1) 2+
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2) 2
3) 4
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Solution
A. The Group number for sulfur is
3) 6A(16)
B. The number of valence electrons in sulfur is
2) 6e
C. The change in electrons for octet requires a
1) gain of 2e
D. The ionic charge of sulfur is
2) 2
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Sizes of Atoms and Their Ions
Metals
 lose their valence electrons
 form ions that are smaller than their atoms
Nonmetals (in ionic compounds)
 gain valence electrons
 form ions that are larger than their atoms
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Metal Ions are Smaller
In Group 1A(1), the ions are
smaller than their
corresponding atoms.
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Nonmetal Ions are Larger
In Group 7A(17), the ions are
larger than their
corresponding atoms.
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Learning Check
Select the larger atom or ion in the following:
1. Mg or Mg2+
2. S or S2
3. Br or Br
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Solution
Select the larger atom or ion in the following:
1. Mg or Mg2+
Mg
2. S or S2
S2
3. Br or Br
Br
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