Chapter 4 Compounds and Their Bonds
4.1 Octet Rule and Ions
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Octet RuleAn octet• is 8 valence electrons.• is associated with the stability of the noble
gases.
He is stable with 2 valence electrons (duet).
valence electrons
He 2 2
Ne 2, 8 8
Ar 2, 8, 8 8
Kr 2, 8, 14, 8 8
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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.
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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 ion 1+
Group 2A metals ion 2+
Group 3A metals ion 3+
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Formation of a Sodium Ion, Na+
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Charge of Sodium Ion, Na+
With the loss of its valence electron,
the sodium ion has a 1+ charge.
Na atom Na+ ion 11p+ 11p+
11e- 10e-
0 1+
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Formation of 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 valenceelectrons, magnesium forms
apositive ion with a 2+
charge.
Mg atom Mg2+ ion 12p+
12p+
12e- 10e-
0 2+
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Learning Check
A. The number of valence electrons in aluminum is1) 1e-. 2) 2e-. 3) 3e-.
B. The change in electrons for octet requires a1) loss of 3e-. 2) gain of 3e-. 3) a gain of 5e-.
C. The ionic charge of aluminum is1) 3-. 2) 5-. 3) 3+.
D. The symbol for the aluminum ion is1) Al3+. 2) Al3-. 3) Al+.
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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 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 1 electron, the chloride ion has a 1- charge.
Chlorine atom, Cl Chloride ion, Cl –
17p+ 17p+
17e- 18e-
0 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 Ionic Charges
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Learning CheckA. The number of valence electrons in sulfur is
1) 4e-. 2) 6e-. 3) 8e-.
B. The change in electrons for octet requires a1) 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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Chapter 4 Compounds and Their Bonds
4.2Ionic Compounds
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Ionic CompoundsIonic compounds
• consist of positive and negative ions.
• have attractions called ionic bonds between positively and negatively charged ions.
• have high melting and boiling points.
• are solid at room temperature.
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Salt Is An Ionic Compound
Sodium chloride or “table salt” is an example of an ionic compound.
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Ionic FormulasAn ionic formula
• consists of positively and negatively charged ions.
• is neutral.
• has charge balance. total positive charge = total negative
charge
The symbol of the metal is written first, followed by the symbol of the nonmetal.
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Charge Balance for NaCl, “Salt”
In NaCl,
• a Na atom loses its valence electron. • a Cl atom gains an electron.• the symbol of the metal is written first,
followed by the symbol of the nonmetal.
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Charge Balance in MgCl2
In MgCl2,
• a Mg atom loses 2 valence electrons.
• two Cl atoms each
gain 1 electron.
• subscripts indicate the number of ions needed to give charge balance.
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Charge Balance in Na2S
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In Na2S,
• two Na atoms lose 1 valence electron each.
• one S atom gains 2 electrons.
• subscripts show the number of ions needed to give charge balance.
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Writing Ionic Formulas from Charges
Charge balance is used to write the formula for
sodium nitride, a compound containing Na+ and N3−.
Na+
3 Na+ + N3− = Na3N
Na+
3(+1) + 1(3-) = 0
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Formula from Ionic Charges Write the ionic formula of the compound with Ba2+
and Cl.
• Write the symbols of the ions.
Ba2+ Cl
• Balance the charges.
Ba2+ Cl two Cl- needed Cl
• Write the ionic formula using a subscript 2 for
two chloride ions.
BaCl224
Learning CheckSelect the correct formula for each of the following ionic compounds.
A. Na+ and O2-
1) NaO 2) Na2O 3) NaO2
B. Al3+ and Cl-
1) AlCl3 2) AlCl 3) Al3Cl
C. Mg2+ and N3-
1) MgN 2) Mg2N3 3) Mg3N2
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Chapter 4 Compounds and Their Bonds
4.3Naming and Writing Ionic
Formulas
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Naming Ionic Compounds with Two Elements
To name a compound that contains two elements,
• identify the cation and anion.
• name the cation first, followed by the name of the anion with an –ide ending.
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Charges of Representative Elements
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Names of Some Common Ions
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Learning CheckComplete the names of the following ions: Ba2+ Al3+ K+
_________ __________ _________
N3 O2 F
_________ __________ _________
P3 S2 Cl _________ __________ _________
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Examples of Ionic Compounds with Two Elements Formula Ions Name
cation anion
NaCl Na+ Cl- sodium chloride
K2S K+ S2- potassium sulfide
MgO Mg2+ O2- magnesium oxide
CaI2 Ca2+ I- calcium iodide
Al2O3 Al3+ O2- aluminum oxide
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Learning CheckWrite the names of the following compounds:
1) CaO___________
2) KBr ___________
3) Al2O3___________
4) MgCl2 ___________
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Learning Check
Write the formulas and names for compounds of the following ions:
Br− S2− N3−
Na+
Al3+
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Transition Metals Form Positive Ions
Most transition metals and Group 4 (14) metals form 2 or more positive ions. However, Zn2+, Ag+, and Cd2+ form only one ion.
Metals That Form More Than One Cation
The name of metals
with two or more
positive ions
(cations) use a
Roman numeral to
identify ionic charge.
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Naming Variable Charge Metals
Transition metals with two different ions use a Roman numeral after the name of the metal to indicate ionic charge.
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Naming FeCl2
To name FeCl2:1. Determine the charge of the cation using the
charge of the anion (Cl-).
Fe ion + 2 Cl- = Fe ion + 2- = 0Fe ion = 2+
2. Name the cation by the element name and add a Roman numeral in parentheses to show its charge.
Fe2+ = iron(II)3. Write the anion with an ide ending. FeCl2 = iron(II) chloride
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Naming Cr2O3To name Cr2O3:1. Determine the charge of cation from the anion
(O2-).2 Cr ions + 3 O2- = 02 Cr ions + 3 (2-) = 0 2 Cr ions - 6 = 02 Cr ions = 6+ Cr ion = 3+ = Cr3+
2. Name the cation by the element name and add a Roman numeral in parentheses to show its charge.
Cr3+ = chromium(III)3. Write the anion with an ide ending. chromium(III) oxide = Cr2O3
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Learning CheckSelect the correct name for each.A. Fe2S3
1) iron sulfide 2) iron(II) sulfide 3) iron(III) sulfide
B. CuO 1) copper oxide 2) copper(I) oxide 3) copper(II) oxide
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Writing FormulasWrite a formula for potassium sulfide.
1. Identify the cation and anion. potassium = K+
sulfide = S2−
2. Balance the charges. K+ S2−
K+
2(1+) + 2(1-) = 0
3. 2 K+ and 1 S2− = K2S
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Writing FormulasWrite a formula for iron(III) chloride.
1. Identify the cation and anion.
iron (III) = Fe3+ (III = charge of 3+)
chloride = Cl−
2. Balance the charges.
Fe3+ Cl−
Cl− = (3+) + 3(1-) = 0
Cl−
3. 1 Fe3+ and 3 Cl− = FeCl3
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Learning CheckWhat is the correct formula for each of the
following?
A. Copper(I) nitride
1) CuN 2) CuN3 3) Cu3N
B. Lead(IV) oxide
1) PbO2 2) PbO 3) Pb2O4
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