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1
Chapter 4 Compounds and Their Bonds
4.1 Octet Rule and Ions
Copyright © 2009 by Pearson Education, Inc.
2
An octet• is 8 valence electrons.• is associated with the stability of the noble gases.
He is stable with 2 valence electrons (duet).
valence electronsHe 2 2Ne 2, 8 8Ar 2, 8, 8 8Kr 2, 8, 14, 8 8
Octet Rule
3
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.
4
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.
5
Formation of a Sodium Ion, Na+
6
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+
2, 8
Copyright © 2009 by Pearson Education, Inc.
7
Formation of Mg2+
Magnesium achieves an octet by losing its two valence electrons.
8
Charge of Magnesium Ion, Mg2+
With the loss of two valenceelectrons, magnesium forms apositive ion with a 2+ charge.
Mg atom Mg2+ ion12p+ 12p+
12e- 10e-
0 2+
Copyright © 2009 by Pearson Education, Inc.
9
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+.
10
Solution
A. The number of valence electrons in aluminum is3) 3 e-.
B. The change in electrons for octet requires a1) loss of 3e-.
C. The ionic charge of aluminum is3) 3+.
D. The symbol for the aluminum ion is1) Al3+.
11
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.
12
Formation of a Chloride, Cl-
Chlorine achieves an octet by adding an electron to its valence electrons.
13
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–
Copyright © 2009 by Pearson Education, Inc.
14
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-
15
Some Ionic Charges
16
A. The number of valence electrons in sulfur is1) 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 is1) 2+. 2) 2-. 3) 4-.
Learning Check
17
A. The number of valence electrons in sulfur is2) 6e-.
B. The change in electrons for octet requires a2) gain of 2e-.
C. The ionic charge of sulfur is2) 2-.
Solution
18
Chapter 4 Compounds and Their Bonds
4.2Ionic Compounds
Copyright © 2009 by Pearson Education, Inc.
19
Ionic 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.
Ionic Compounds
20
Salt Is An Ionic Compound
Sodium chloride or “table salt” is an example of an ionic compound.
21
An 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.
Ionic Formulas
22
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.
23
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.
Copyright © 2009 by Pearson Education, Inc.
24
Charge Balance in Na2S
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. Copyright © 2009 by Pearson Education, Inc.
25
Writing Ionic Formulas from Charges
Charge balance is used to write the formula forsodium nitride, a compound containing Na+ and N3−.
Na+
3 Na+ + N3− = Na3NNa+
3(+1) + 1(3-) = 0
26
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. BaCl2
Formula from Ionic Charges
27
Select 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
Learning Check
28
A. Na+ and O2-
2) Na2O check: 2Na+ + O2- = 2(1+) + 1(2-) = 0
B. Al3+ and Cl-1) AlCl3
check: Al3+ + Cl- = (3+) + 3(1-) = 0
C. Mg2+ and N3-
3) Mg3N2 check: 2Mg2+ +2N3- = 2(3+) + 2(3-) = 0
Solution
29
Chapter 4 Compounds and Their Bonds
4.3Naming and Writing Ionic
Formulas
Copyright © 2009 by Pearson Education, Inc.
30
Naming Ionic Compounds with Two Elements
To name a compound that contains two elements,
• identify the cationand anion.
• name the cation first, followed by the name of the anion with an –ide ending.
31
Charges of Representative Elements
Copyright © 2009 by Pearson Education, Inc.
32
Names of Some Common Ions
33
Complete the names of the following ions:
Ba2+ Al3+ K+
_________ __________ _________
N3− O2− F−
_________ __________ _________
P3− S2− Cl−_________ __________ _________
Learning Check
34
Ba2+ Al3+ K+
barium aluminum potassium
N3− O2− F−
nitride oxide fluoride
P3− S2− Cl−phosphide sulfide chloride
Solution
35
Formula Ions Namecation anion
NaCl Na+ Cl- sodium chlorideK2S K+ S2- potassium sulfideMgO Mg2+ O2- magnesium oxideCaI2 Ca2+ I- calcium iodideAl2O3 Al3+ O2- aluminum oxide
Examples of Ionic Compounds with Two Elements
36
Write the names of the following compounds:
1) CaO ___________
2) KBr ___________
3) Al2O3 ___________
4) MgCl2 ___________
Learning Check
37
Write the names of the following compounds:
1) CaO calcium oxide2) KBr potassium bromide3) Al2O3 aluminum oxide4) MgCl2 magnesium chloride
Solution
38
Learning Check
Write the formulas and names for compounds of the following ions:
Br− S2− N3−
Na+
Al3+
39
Solution
Br− S2− N3−
Na+
Al3+
NaBrsodium bromide
Na2Ssodium sulfide
Na3Nsodium nitride
AlBr3aluminum bromide
Al2S3aluminum sulfide
AlNaluminum nitride
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.
41
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.
42
Naming Ionic Compounds with Variable Charge Metals
43
Naming Variable Charge Metals
Transition metals with two different ions use a Roman numeral after the name of the metal to indicate ionic charge.
44
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 aRoman numeral in parentheses to show its charge.
Fe2+ = iron(II)3. Write the anion with an ide ending.
FeCl2 = iron(II) chloride
45
Naming Cr2O3
To 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 aRoman numeral in parentheses to show its charge.
Cr3+ = chromium(III)3. Write the anion with an ide ending.
chromium(III) oxide = Cr2O3
46
Learning Check
Select the correct name for each.A. Fe2S3
1) iron sulfide2) iron(II) sulfide3) iron(III) sulfide
B. CuO1) copper oxide2) copper(I) oxide 3) copper(II) oxide
47
Solution
Select the correct name for each.A. Fe2S3
3) iron (III) sulfide Fe3+ S2-
B. CuO3) copper (II) oxide Cu2+ O2-
48
Guide to Writing Formulas from the Name
Copyright © 2009 by Pearson Education, Inc.
49
Writing Formulas
Write 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
50
Writing Formulas
Write 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-) = 0Cl−
3. 1 Fe3+ and 3 Cl− = FeCl3
51
Learning Check
What is the correct formula for each of the following?A. Copper(I) nitride
1) CuN 2) CuN3 3) Cu3N
B. Lead(IV) oxide1) PbO2 2) PbO 3) Pb2O4
52
Solution
The correct formula isA. Copper(I) nitride
3) Cu3N Need 3 Cu+ and N3-
B. Lead(IV) oxide1) PbO2 Need Pb4+ and 2 O2-
53
4.4 Polyatomic Ions
Chapter 4 Compounds and Their Bonds
Copyright © 2009 by Pearson Education, Inc.
54
A polyatomic ion• is a group of atoms. • has an overall ionic charge.
Some examples of polyatomic ions areNH4
+ ammonium OH− hydroxideNO3
− nitrate NO2− nitrite
CO32− carbonate PO4
3− phosphateHCO3
− hydrogen carbonate(bicarbonate)
Polyatomic Ions
55
Some Compounds with Polyatomic Ions
Copyright © 2009 by Pearson Education, Inc.
56
The names of common polyatomic anions • end in ate.
NO3− nitrate PO4
3− phosphate• with one oxygen less end in ite.
NO2− nitrite PO3
3− phosphite• with hydrogen attached use the prefix hydrogen (or bi).
HCO3− hydrogen carbonate (bicarbonate)
HSO3− hydrogen sulfite (bisulfite)
Some Names of Polyatomic Ions
57
Names and Formulas of Common Polyatomic Ions
58
• The positive ion is named first, followed by the name of the polyatomic ion.
NaNO3 sodium nitrateK2SO4 potassium sulfateFe(HCO3)3 iron(III) bicarbonate
or iron(III) hydrogen carbonate(NH4)3PO3 ammonium phosphite
Naming Compounds with Polyatomic Ions
Guide to Naming Compounds with Polyatomic Ions
59
60
Some Compounds with Polyatomic Ions
61
Match each formula with the correct name.
A. MgS 1) magnesium sulfite MgSO3 2) magnesium sulfateMgSO4 3) magnesium sulfide
B. Ca(ClO3)2 1) calcium chlorateCaCl2 2) calcium chloriteCa(ClO2)2 3) calcium chloride
Learning Check
62
Match each formula with the correct name.
A. MgS 3) magnesium sulfideMgSO3 1) magnesium sulfite MgSO4 2) magnesium sulfate
B. Ca(ClO3)2 1) calcium chlorateCaCl2 3) calcium chlorideCa(ClO2)2 2) calcium chlorite
Solution
63
Learning Check
Name each of the following compounds:
A. Mg(NO3)2
B. Cu(ClO3)2
C. PbO2
D. Fe2(SO4)3
E. Ba3(PO3)2
64
Solution
Name each of the following compounds:
A. Mg(NO3)2 magnesium nitrateB. Cu(ClO3)2 copper(II) chlorateC. PbO2 lead(IV) oxideD. Fe2(SO4)3 iron(III) sulfateE. Ba3(PO3)2 barium phosphite
65
Writing Formulas with Polyatomic Ions
The formula of an ionic compound • containing a polyatomic ion must have a charge
balance that equals zero (0).Na+ and NO3
− -> NaNO3
• with two or more polyatomic ions has the polyatomic ions in parentheses.Mg2+ and 2NO3
− -> Mg(NO3)2
subscript 2 for charge balance
66
Select the correct formula for each.A. aluminum nitrate
1) AlNO3 2) Al(NO)3 3) Al(NO3)3
B. copper(II) nitrate1) CuNO3 2) Cu(NO3)2 3) Cu2(NO3)
C. iron(III) hydroxide1) FeOH 2) Fe3OH 3) Fe(OH)3
D. tin(IV) hydroxide1) Sn(OH)4 2) Sn(OH)2 3) Sn4(OH)
Learning Check
67
Select the correct formula for each.
A. aluminum nitrate 3) Al(NO3)3
B. copper(II) nitrate 2) Cu(NO3)2
C. iron(III) hydroxide 3) Fe(OH)3
D. tin(IV) hydroxide 1) Sn(OH)4
Solution
68
Learning Check
Write the correct formula for each.
A. potassium bromateB. calcium carbonateC. sodium phosphateD. iron(III) oxideE. iron(II) nitrite
69
Solution
Write the correct formula for each.A. potassium bromate KBrO3
B. calcium carbonate CaCO3
C. sodium phosphate Na3PO4
D. iron(III) oxide Fe2O3
E. iron(II) nitrite Fe(NO2)2
70
Flowchart for Naming Ionic Compounds
71
Learning Check
Name the following compounds:A. Ca3(PO4)2
B. FeBr3
C. Al2S3
D. Zn(NO2)2
E. NaHCO3
72
Solution
Name the following compounds:A. Ca3(PO4)2Ca2+ PO4
3− calcium phosphateB. FeBr3 Fe3+ Br − iron(III) bromideC. Al2S3 Al3+ S2− aluminum sulfideD. Zn(NO2)2 Zn2+ NO2
− zinc nitriteE. NaHCO3 Na+ HCO3
− sodium hydrogen carbonateor sodium bicarbonate
73
Learning Check
Write the formulas for the following:A. calcium nitrate
B. iron(II) hydroxide
C. aluminum carbonate
D. copper(II) bromide
E. lithium phosphate
74
Solution
Write the formulas for the following:A. calcium nitrate Ca2+, NO3
− Ca(NO3)2
B. iron(II) hydroxide Fe2+, OH− Fe(OH)2
C. aluminum carbonate Al3+, CO32− Al2(CO3)3
D. copper(II) bromide Cu2+, Br− CuBr2
E. lithium phosphate Li+, PO43− Li3PO4
75
Chapter 4 Compounds and Their Bonds
4.5Covalent Compounds
Copyright © 2009 by Pearson Education, Inc.
76
Covalent bonds form
• when atoms share electrons to complete octets.
• between two nonmetal atoms.
• between nonmetal atoms from Groups 4A (14), 5A (15), 6A (16), and 7A (17).
Covalent Bonds
77
Hydrogen Molecule
A hydrogen molecule
• is stable with 2 electrons (helium).
• has a shared pair of electrons.
78
Forming Octets in Molecules
In a fluorine, F2,, molecule, each F atom
• shares 1 electron.
• attains an octet.
79
Carbon Forms 4 Covalent Bonds
In a CH4 (methane) molecule,
• 1 C atom shares electrons with 4 H atoms to attain an octet.
• each H atom shares 1 electron to become stable, like helium.
80
Multiple Bonds
In a nitrogen molecule, N2,
• each N atom shares 3 electrons.• each N attains an octet.• the bond is a multiple bond called a triple bond.• the name is the same as the element.
Copyright © 2009 by Pearson Education, Inc.
81
Naming Covalent Compounds
In the names of covalent compounds, prefixes are used to indicate the number of atoms (subscript) of each element. (mono is usually omitted)
82
Guide to Naming Covalent Compounds
83
What is the name of SO3?
1. The first nonmetal is S sulfur. 2. The second nonmetal is O, named oxide.3. The subscript 3 of O is shown as the prefix tri.
SO3 -> sulfur trioxide
The subscript 1 (for S) or mono is understood.
Naming Covalent Compounds
84
Name P4S3.
1. The first nonmetal, P, is phosphorus. 2. The second nonmetal, S, is sulfide.3. The subscript 4 of P is shown as tetra.
The subscript 3 of O is shown as tri.
P4S3 -> tetraphosphorus trisulfide
Naming Covalent Compounds
85
Formulas and Names of Some Covalent Compounds
86
Select the correct name for each compound.A. SiCl4 1) silicon chloride
2) tetrasilicon chloride3) silicon tetrachloride
B. P2O5 1) phosphorus oxide2) phosphorus pentoxide3) diphosphorus pentoxide
C. Cl2O7 1) dichlorine heptoxide2) dichlorine oxide3) chlorine heptoxide
Learning Check
87
Select the correct name for each compound.
A. SiCl4 3) silicon tetrachlorideB. P2O5 3) diphosphorus pentoxideC. Cl2O7 1) dichlorine heptoxide
Solution
88
Write the name of each covalent compound.
CO _____________________CO2 _____________________PCl3 _____________________CCl4 _____________________N2O _____________________
Learning Check
89
Write the name of each covalent compound.
CO carbon monoxideCO2 carbon dioxidePCl3 phosphorus trichlorideCCl4 carbon tetrachlorideN2O dinitrogen oxide
Solution
90
Guide to Writing Formulas for Covalent Compounds
91
Write the formula for carbon disulfide.
STEP 1: Elements are C and SSTEP 2: No prefix for carbon means 1 C
Prefix di = 2Formula: CS2
Example: Writing Formulas for Covalent Compounds
92
Write the correct formula for each of the following:
A. phosphorus pentachloride
B. dinitrogen trioxide
C. sulfur hexafluoride
Learning Check
93
Write the correct formula for each of the following:
A. phosphorus pentachloride 1 P penta = 5 Cl PCl5
B. dinitrogen trioxidedi = 2 N tri = 3 O N2O3
C. sulfur hexafluoride
1 S hexa = 6 F SF6
Solution
94
Learning Check
Identify each compound as ionic or covalent, and give itscorrect name.
A. SO3
B. BaCl2C. (NH4)3PO3
D. Cu2CO3
E. N2O4
95
Study Tip: Ionic or Covalent
A compound is• ionic if the first element in the formula
or the name is a metal or the polyatomic ion NH4+ .
K2O K is a metal; compound is ionic; potassium oxide
• covalent if the first element in the formula or the name is a nonmetal.
N2O N is a nonmetal; compound is covalent; dinitrogen oxide
96
Solution
Identify each compound as ionic or covalent and give itscorrect name.
A. SO3 covalent – sulfur trioxideB. BaCl2 ionic – barium chlorideC. (NH4)3PO3 ionic – ammonium phosphiteD. Cu2CO3 ionic – copper(I) carbonateE. N2O4 covalent – dinitrogen tetroxide
97
Learning Check
Identify each compound as ionic or covalent and give itscorrect name.
A. Ca3(PO4)2B. FeBr3
C. SCl2D. Cl2OE. N2
98
Solution
Identify each compound as ionic or covalent and give itscorrect name.
A. Ca3(PO4) ionic Ca2+ PO43− calcium phosphate
B. FeBr3 ionic Fe3+ Br − iron(III) bromideC. SCl2 covalent 1S 2 Cl sulfur dichlorideD. Cl2O covalent 2 Cl 1 O dichlorine oxideE. N2 covalent element nitrogen
99
Learning Check
Determine if each is ionic (I) or covalent (C ), and write the formula.
A. calcium nitrate
B. boron trifluoride
C. aluminum carbonate
D. dinitrogen tetroxide
E. copper(I) phosphate
100
Solution
Determine if each is ionic (I) or covalent (C ), and write the formula.
A. calcium nitrate (I) Ca2+, NO3− Ca(NO3)2
B. boron trifluoride (C) 1 B, 3 F BF3
C. aluminum carbonate (I) Al3+, CO32− Al2(CO3) 3
D. dinitrogen tetroxide (C) 2 N, 4 O N2O4
E. copper(I) phosphate (I) Cu+, PO43− Cu3PO4
101
Chapter 4 Compounds and Their Bonds
4.6 Electronegativity and Bond Polarity
Copyright © 2009 by Pearson Education, Inc.
102
The electronegativity value
• indicates the attraction of an atom for shared electrons.
• increases from left to right going across a period on the periodic table.
• is high for the nonmetals, with fluorine as the highest.
• is low for the metals.
Electronegativity
103
Some Electronegativity Values for Group A Elements
Low values
High values
`Electronegativity increases
`E
lectronegativity decreases
Copyright © 2009 by Pearson Education, Inc.
104
A nonpolar covalent bond
• occurs between nonmetals.• is an equal or almost equal sharing of electrons.• has almost no electronegativity difference (0.0 to 0.4).
Examples: Electronegativity
Atoms Difference Type of BondN-N 3.0 - 3.0 = 0.0 Nonpolar covalentCl-Br 3.0 - 2.8 = 0.2 Nonpolar covalentH-Si 2.1 - 1.8 = 0.3 Nonpolar covalent
Nonpolar Covalent Bonds
105
A polar covalent bond
• occurs between nonmetal atoms.• is an unequal sharing of electrons.• has a moderate electronegativity difference (0.5 to 1.7).
Examples: Electronegativity
Atoms Difference Type of BondO-Cl 3.5 - 3.0 = 0.5 Polar covalentCl-C 3.0 - 2.5 = 0.5 Polar covalentO-S 3.5 - 2.5 = 1.0 Polar covalent
Polar Covalent Bonds
106
Comparing Nonpolar and Polar Covalent Bonds
Copyright © 2009 by Pearson Education, Inc.
107
Ionic Bonds
An ionic bond• occurs between metal and nonmetal ions.• is a result of electron transfer.• has a large electronegativity difference (1.8 or more).
Examples: Electronegativity
Atoms Difference Type of BondCl-K 3.0 – 0.8 = 2.2 IonicN-Na 3.0 – 0.9 = 2.1 IonicS-Cs 2.5 – 0.7 = 1.8 Ionic
108
Electronegativity and Bond Types
109
Predicting Bond Types
110
Use the electronegativity difference to identify the type of bond [nonpolar covalent (NP), polar covalent (P), or ionic (I)] between the following:
A. K-NB. N-OC. Cl-ClD. H-Cl
Learning Check
111
Use the electronegativity difference to identify the type of bond [nonpolar covalent (NP), polar covalent (P), or ionic (I)] between the following:
A. K-N 2.2 ionic (I) B. N-O 0.5 polar covalent (P)C. Cl-Cl 0.0 nonpolar covalent (NP) D. H-Cl 0.9 polar covalent (P)
Solution
112
Chapter 4 Compounds and Their Bonds
4.7Shapes and Polarity of Molecules
Copyright © 2009 by Pearson Education, Inc.
°
113
VSEPR
In the valence-shell electron-pair repulsion theory(VSEPR), the electron groups around a central atom
• are arranged as far apart from each other as possible.
• have the least amount of repulsion of the negatively charged electrons.
• have a geometry around the central atom that determines molecular shape.
Guide to Predicting Molecular Shape
114
115
Four Electron Groups
In a molecule of CH4,• there are 4 electron groups
around C. • repulsion is minimized by
placing 4 electron groups at angles of 109°, which is a tetrahedral arrangement.
• the shape with four bonded atoms is tetrahedral.
Copyright © 2009 by Pearson Education, Inc.
116
Three Bonding Atoms and One Lone Pair
In a molecule of NH3,• 3 electron groups bond to H atoms, and the fourth one
is a lone (nonbonding) pair.• repulsion is minimized with 4 electron groups in a
tetrahedral arrangement.• with 3 bonded atoms, the shape is pyramidal.
117
Two Bonding Atoms and Two Lone Pairs
In a molecule of H2O,• 2 electron groups are bonded to H atoms and 2 are lone
pairs (4 electron groups).• 4 electron groups minimize repulsion in a tetrahedral
arrangement.• the shape with 2 bonded atoms is bent.
Electron Pairs
Bonded Atoms
Lone Pairs
Molecular Shape
Example
4 4 0 Tetrahedral CH4
4 3 1 Pyramidal NH3
4 2 2 Bent H2O
Shapes with 4 Electron Groups
Copyright © 2009 by Pearson Education, Inc. 118
119
Learning Check
State the number of electron groups, lone pairs, and use VSEPR theory to determine the shape of the following molecules or ions.1) tetrahedral 2) pyramidal 3) bent
A. PF3
B. H2SC. CCl4
120
Study Tip
To determine shape, 1. draw the electron-dot structure.2. count the electron pairs around the central atom.3. count the bonded atoms to determine shape.
4 electron pairs and 4 bonded atoms = tetrahedral4 electrons pairs and 3 bonded atoms = pyramidal4 electron pairs and 2 bonded atoms = bent
121
Solution
A. PF3
4 electron groups, 1 lone pair, (2) pyramidalB. H2S
4 electron groups, 2 lone pairs, (3) bentC. CCl4
4 electron groups, 0 lone pairs, (1) tetrahedral
122
Polar Molecules
A polar molecule• contains polar bonds.• has a separation of positive and negative charge
called a dipole, indicated with δ+ and δ-.• has dipoles that do not cancel.
δ+ δ-• •
H–Cl H—N—Hdipole
Hdipoles do not cancel
123
Nonpolar Molecules
A nonpolar molecule• contains nonpolar bonds.
Cl–Cl H–H
• or has a symmetrical arrangement of polar bonds.O=C=O Cl
Cl–C–Cl
Cldipoles cancel
124
Determining Molecular Polarity
STEP 1: Write the electron-dot formula.STEP 2: Determine the shape.STEP 3: Determine if dipoles cancel or not.
Example: H2O. .
H O: H2O is polar
Hdipoles do not cancel
125
Learning Check
Identify each of the following molecules as 1) polar or 2) nonpolar. Explain.
A. PBr3B. HBrC. Br2D. SiBr4
126
Solution
Identify each of the following molecules as 1) polar or 2) nonpolar. Explain.
A. PBr3 1) pyramidal; dipoles do not cancel; polar
B. HBr 1) linear; one polar bond (dipole); polar
C. Br2 2) linear; nonpolar bond; nonpolar
D. SiBr4 2) tetrahedral; dipoles cancel; nonpolar