1. Chapter 4 Compounds and Their Bonds
4.4
Polyatomic Ions
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

2. Polyatomic Ions Polyatomic Ions
are a group of atoms with an overall charge
often consist of a nonmetal such as phosphorus, sulfur,
carbon, or nitrogen and oxygen
usually have a 1−, 2−, or 3− charge
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

3. Names of Polyatomic Ions
1. Names of most common polyatomic ions end in ate.
SO42− sulfate
PO43− phosphate
NO3− nitrate
2. When a related ion has one less oxygen, its name ends in ite.
SO32− sulfite
PO33− phosphite
NO2− nitrite
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

4. Names of Polyatomic Ions
3. Exceptions to these rules are:
CN− cyanide
OH− hydroxide
NH4+ ammonium
4. Add an H+ and reduce negative charge.
CO32− + H+ = HCO3−
carbonate + H+ = bicarbonate or hydrogen carbonate
SO42− + H+ = HSO4−
sulfate + H+ = bisulfate or hydrogen sulfate
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

5. Names of Polyatomic Ions
5. Halogens form 4 polyatomic
ions with oxygen
each have a 1 charge.
ClO4− perchlorate
ClO3− chlorate
ClO2− chlorite
ClO− hypochlorite
Sodium chlorite is used in the processing and bleaching of pulp from wood fibers and recycled cardboard.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

6. Compounds Containing Polyatomic Ions
When writing formulas for ionic compounds containing polyatomic ions, we use the same rules of charge balance as those for simple ionic compounds.
Consider the formula for magnesium nitrate:
Mg NO3−
NO3−
(2+) (1−) = 0
Mg NO3− = Mg(NO3)2
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

7. Learning Check Select the correct formula for each.
A. aluminum nitrate
1) AlNO3 2) Al(NO)3 3) Al(NO3)3
B. copper(II) nitrate
1) CuNO3 2) Cu(NO3)2 3) Cu2(NO3)
C. iron(III) hydroxide
1) FeOH 2) Fe3OH 3) Fe(OH)3
D. tin(IV) hydroxide
1) Sn(OH)4 2) Sn(OH)2 3) Sn4(OH)
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

8. Solution Select the correct formula for each.
A. aluminum nitrate 3) Al(NO3)3
B. copper(II) nitrate ) Cu(NO3)2
C. iron(III) hydroxide ) Fe(OH)3
D. tin(IV) hydroxide ) Sn(OH)4
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

9. Guide to Naming Ionic Compounds with Polyatomic Ions
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

10. Naming Compounds with Polyatomic Ions
Name the following ionic compounds:
Step 1 Step 2 Step Step 4
cation/anion Name Name Name
cation anion compound
A. Ca(NO3)2 Ca2+ NO3− calcium nitrate calcium nitrate
B. FePO4 Fe3+ PO43− iron(III) phosphate iron(III) phosphate
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

11. Learning Check
Name each of the following compounds containing polyatomic ions.
A. MgSO3
B. MgSO4
C. Ca(ClO3)2
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

12. Solution Name the following ionic compounds:
Step 1 Step 2 Step Step 4
cation/anion Name Name Name
cation anion compound
A. MgSO3 Mg2+ SO32− magnesium sulfite magnesium
sulfite
B. MgSO4 Mg2+ SO42− magnesium sulfate magnesium
sulfate
C. Ca(ClO3)2 Ca2+ ClO3− calcium chlorate calcium
chlorate
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

13. Learning Check Name each of the following compounds: A. Fe2(SO4)3
B. Ba3(PO3)2
C. PbCO3
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

14. Solution Name the following ionic compounds:
Step 1 Step 2 Step Step 4
cation/anion Name Name Name
cation anion compound
A. Fe2(SO4)3 Fe3+ SO42− iron(III) sulfate iron(III)
sulfate
B. Ba3(PO3)2 Ba2+ PO33− barium phosphite barium
phosphite
C. PbCO3 Pb2+ CO32− lead(II) carbonate lead(II)
carbonate
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

15. Chapter 4 Compounds and Their Bonds
4.5
Covalent Compounds and Their Names
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

16. Covalent Bonds Covalent compounds form
when atoms share electrons to complete octets
between nonmetal atoms from Groups 4A, 5A, 6A, and 7A
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

17. Formation of a Hydrogen Molecule
A hydrogen molecule, H2,
forms as the atoms move closer and the nucleus of one atom attracts the electron of the other
is stable with 2 electrons (helium)
has a shared pair of electrons
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

18. Formation of a Hydrogen Molecule – H2
A covalent bond forms as H atoms move close together to share electrons.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

19. Formation of Octets in Molecules – F2
In a fluorine, F2,, molecule, each F atom shares one electron to attain an octet.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

20. Writing Electron-Dot Formulas
To draw the electron-dot formula for methane, CH4,
we start with the electron-dot symbols for carbon and hydrogen
we need four hydrogen atoms to complete carbon’s octet
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

21. Double and Triple Covalent Bonds
A double bond:
occurs when atoms share two pairs of electrons
forms when there are not enough electrons to complete octets
A triple bond:
occurs when atoms share three pairs of electrons
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

22. Guide to Drawing Electron-Dot Formulas
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

23. Electron-Dot Formulas for Some Covalent Compounds – CO2
Step 1 Determine the arrangement of atoms. O C O
Step 2 Determine the total number of valence electrons.
C 2(O) = CO2
4e− + 2(6−) = 16e−
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

24. Electron-Dot Formulas for Some Covalent Compounds – CO2
Step 3 Attach each bonded atom to the central atom
with a pair of electrons.
Step 4 Place the remaining electrons using single or
multiple bonds to complete octets.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

25. Triple Bond – N2 In a nitrogen molecule, N2,
each N atom shares three electrons to gain an octet
the multiple bond formed is called a triple bond
the name is the same as the element
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

26. Names and Formulas of Covalent Compounds
When naming covalent compounds:
the first nonmetal in the formula is named by its element name
the second nonmetal is named by using the first syllable of its name followed by ide
if a subscript is used in the formula a prefix is used in front of its name
when vowels o and o or a and o appear together, the first vowel is omitted
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

27. Guide to Naming Covalent Compounds
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

28. Prefixes Used in Naming Covalent Compounds
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

29. Naming Covalent Compounds – NCl3
Name the covalent compound NCl3.
Step 1 Name the first nonmetal by its element name.
The first nonmetal (N) is nitrogen.
Step 2 Name the second element by using the first
syllable of its name followed by ide.
The second nonmetal (Cl) is chloride.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

30. Naming Covalent Compounds – NCl3
Step 3 Add prefixes to indicate number of atoms.
Because there is one nitrogen atom, no prefix
is needed.
The subscript three for the Cl atoms is shown as the
prefix tri.
NCl3, nitrogen trichloride
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

31. Some Common Covalent Compounds
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

32. Learning Check Select the correct name for each compound.
A. SiCl4 1) silicon chloride
2) tetrasilicon chloride
3) silicon tetrachloride
B. P2O5 1) phosphorus oxide
2) phosphorus pentoxide
3) diphosphorus pentoxide
C. Cl2O7 1) dichlorine heptoxide
2) dichlorine oxide
3) chlorine heptoxide
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

33. Solution Select the correct name for each compound.
A. SiCl4 3) silicon tetrachloride
B. P2O5 3) diphosphorus pentoxide
C. Cl2O7 1) dichlorine heptoxide
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

34. Learning Check Write the name of each covalent compound. A. CO B. NO2
C. PF3
D. CCl4
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

35. Solution Write the name of each covalent compound.
Step 1 Name the first nonmetal by its element name.
A. CO The first nonmetal (C) is carbon.
B. NO2 The first nonmetal (N) is nitrogen.
C. PF3 The first nonmetal (P) is phosphorus.
D. CCl4 The first nonmetal (C) is carbon.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

36. Solution Write the name of each covalent compound.
Step 2 Name the second element by using the first syllable of its name followed by ide.
A. CO The second nonmetal (O) is oxide.
B. NO2 The second nonmetal (O) is oxide.
C. PF3 The second nonmetal (F) is fluoride.
D. CCl4 The second nonmetal (Cl) is chloride.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

37. Solution Write the name of each covalent compound.
Step 3 Add prefixes to indicate number of atoms.
A. CO Because there is one carbon atom, no prefix is needed. The subscript 1 for the O atom is shown using the prefix mono. CO is carbon monoxide.
B. NO2 Because there is one nitrogen atom, no prefix is needed. The subscript 2 for the O atoms is shown using the prefix di. NO2 is nitrogen dioxide.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

38. Solution Write the name of each covalent compound.
Step 3 Add prefixes to indicate number of atoms.
C. PF3 Because there is one phosphorus atom, no prefix is needed. The subscript 3 for F atoms is shown using the prefix tri. PF3 is phosphorus trifluoride.
D. CCl4 Because there is one carbon atom, no prefix is needed. The subscript 4 for the Cl atoms is shown using the prefix tetra. CCl4 is carbon tetrachloride.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

39. Writing Formulas for Covalent Compounds
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

40. Writing Formulas for Covalent Compounds – Diboron Trioxide
Write the formula for the covalent compound diboron trioxide.
Step 1 Write the symbols in order of the elements in the name.
The first nonmetal is boron (B) and the second nonmetal is oxygen (O). B O
Step 2 Write any prefixes as subscripts. The prefix di in diboron indicates there are two boron atoms and is shown as a subscript after B. The prefix tri in trioxide indicates there are three oxygen atoms and is shown as a subscript after O. B2O3
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

41. Learning Check Write the correct formula for each of the following:
A. phosphorus pentachloride
B. dinitrogen trioxide
C. sulfur hexafluoride
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

42. Solution Write the correct formula for each of the following:
Step 1 Write the symbols in order of the elements in the name.
A. phosphorus pentachloride The first nonmetal is phosphorus, (P) and the second nonmetal is chlorine, (Cl). P Cl
B. dinitrogen trioxide The first nonmetal is nitrogen, (N) and the second nonmetal is oxygen, (O). N O
C. sulfur hexafluoride The first nonmetal is sulfur, (S) and the second nonmetal is fluorine, (F). S F
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

43. Solution Write the correct formula for each of the following:
Step 2 Write any prefixes as subscripts.
A. phosphorus pentachloride: No prefix for phosphorus indicates there is 1 phosphorus atom. The prefix penta in pentachloride indicates there are 5 chlorine atoms, and is shown as a subscript after Cl. PCl5
B. dinitrogen trioxide: The prefix di in dinitrogen indicates there are 2 nitrogen atoms and is shown as a subscript after N. The prefix tri in trioxide indicates there are 3 oxygen atoms and is shown as a subscript after O. N2O3
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

44. Solution Write the correct formula for each of the following:
Step 2 Write any prefixes as subscripts.
C. sulfur hexafluoride: No prefix for sulfur indicates there is 1 sulfur atom. The prefix hexa in hexafluoride indicates there are 6 fluorine atoms and is shown as a subscript after F. SF6
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

45. Summary to Naming Simple Compounds
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

46. Learning Check
Identify each compound as ionic or covalent, and give its correct name.
A. SO3
B. BaCl2
C. (NH4)3PO3
D. Cu2CO3
E. N2O4
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

47. 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
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

48. Solution
Identify each compound as ionic or covalent and give its correct name.
A. SO3 covalent – sulfur trioxide
B. BaCl2 ionic – barium chloride
C. (NH4)3PO3 ionic – ammonium phosphite
D. Cu2CO ionic – copper(I) carbonate
E. N2O4 covalent – dinitrogen tetroxide
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

49. Chapter 4 Compounds and Their Bonds
4.6
Electronegativity and Bond Polarity
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

50. Electronegativity The electronegativity value
of an element indicates the attraction of an atom for the shared electrons in a bond
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
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

51. Electronegativity and the Periodic Table
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

52. Comparing Ionic, Polar, and Nonpolar Covalent Bonds
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

53. Comparing Nonpolar and Polar Bonds
In the nonpolar covalent bond of H2, electrons are shared equally. In the polar covalent bond of HCl, electrons are shared unequally.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

54. Nonpolar Covalent Bonds
A nonpolar covalent bond
occurs between nonmetals
is an equal or almost equal sharing of electrons
has a very small electronegativity difference
Examples:
Electronegativity
Atoms Difference Type of Bond
N-N  3.0 = 0.0 Nonpolar covalent
Cl-Br 3.0  2.8 = 0.2 Nonpolar covalent
H-Si 2.1  1.8 = 0.3 Nonpolar covalent
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

55. Polar Covalent Bonds A polar covalent bond
occurs between nonmetal atoms
is an unequal sharing of electrons
has a moderate electronegativity difference
Examples:
Electronegativity
Atoms Difference Type of Bond
O-Cl  3.0 = 0.5 Polar covalent
Cl-C 3.0  2.5 = 0.5 Polar covalent
O-S  2.5 = 1.0 Polar covalent
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

56. 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 Bond
Cl-K – 0.8 = 2.2 Ionic
N-Na 3.0 – 0.9 = 2.1 Ionic
S-Cs 2.5 – 0.7 = 1.8 Ionic
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

57. Predicting Bond Types
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

58. Learning Check
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
B. N-O
C. Cl-Cl
D. H-Cl
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

59. Solution
Use the electronegativity difference to identify the type of bond [nonpolar covalent (NP), polar covalent (P), or ionic (I)] between the following:
Difference Type of bond
A. K-N ionic (I)
B. N-O polar covalent (P)
C. Cl-Cl 0.0 nonpolar covalent (NP)
D. H-Cl 0.9 polar covalent (P)
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

60. Chapter 4 Compounds and Their Bonds
4.7
Shapes and Polarity of Molecules
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

61. VSEPR Theory Valence Shell Electron-Pair Repulsion Theory (VSEPR)
describes the orientation of electron groups around the central atom
states that electron groups are arranged as far apart as possible around the central atom
states that specific shape of a molecule is determined by the number of atoms attached to the central atom
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

62. Central Atom with Two Electron Groups
In a molecule of BeCl2
there are only two electron groups around the central atom, Be, which is an exception to octet rule
repulsion is minimized by placing the two groups on opposite sides of the Be atom, giving this a linear arrangement with bond angles of 180°
the shape with two electron groups around the central atom is linear
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

63. Central Atom with Three Electron Groups
In a molecule of BF3
there are only three electron groups around the central atom, B, which is an exception to octet rule
repulsion is minimized by placing the three groups as far apart as possible at bond angles of 120°
the shape with three electron groups around the central atom is trigonal planar
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

64. Central Atom with Three Electron Groups
In a molecule of SO2
there are three electron groups around the central atom S:
a single-bonded O atom, a double-bonded O atom, and a lone pair of electrons
repulsion is minimized by placing the three groups as far apart as possible
since one group is a lone pair, the shape is determined by the two O atoms bonded to S, giving the molecule its bent shape
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

65. Central Atom with Four Electron Groups
In a molecule of CH4
there are four electron groups attached to H atoms around the central atom, C
repulsion is minimized by placing the four groups at corners of a tetrahedron with bond angles of 109°
the shape with four bonds on the central atom is called tetrahedral
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

66. Central Atom with Four Electron Groups
In a molecule of NH3
there are three electron groups attached to H atoms and a lone pair around the central atom, N
repulsion is minimized by placing the four groups at corners of a tetrahedron with bond angles of 109°
the shape with three bonds on the central atom is called trigonal pyrimidal
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

67. Central Atom with Four Electron Groups
In a molecule of H2O
there are two electron groups attached to H atoms and two lone pairs around the central atom, O
repulsion is minimized by placing the four groups at corners of a tetrahedron with bond angles of 109°
the shape with two bonds on the central atom is called bent
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

68. Molecular Shapes for Molecules
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

69. Guide to Predicting Molecular Shape
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

70. Predict Molecular Shape of H2S
Predict the shape of H2S.
Step 1 Draw the electron-dot formula.
Step 2 Arrange electron groups around the central atom to minimize repulsion. To minimize repulsion, electron groups have a tetrahedral arrangement.
Step 3 Use the atoms bonded to the central atom determine the molecular shape. With two bonds and two lone pairs, the shape is bent.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

71. Learning Check
State the number of electron groups and lone pairs and use VSEPR theory to determine the shape of the following molecules or ions as tetrahedral, trigonal pyramidal, or bent.
A. PF3
B. H2S
C. CCl4
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

72. Solution
State the number of electron groups and lone pairs and use VSEPR theory to determine the shape of the following molecules or ions as tetrahedral, trigonal pyramidal, or bent.
Step 1 Draw the electron-dot formula.
A. PF3 B. H2S C. CCl4
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

73. Solution
State the number of electron groups, and lone pairs and use VSEPR theory to determine the shape of the following molecules or ions as tetrahedral, trigonal pyramidal, or bent.
Step 2 Arrange electron groups around the central atom to minimize repulsion.
A. PF3 To minimize repulsion electron groups have a tetrahedral arrangement.
B. H2S To minimize repulsion electron groups have a tetrahedral arrangement.
C. CCl4 To minimize repulsion electron groups have a tetrahedral arrangement.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

74. Solution
State the number of electron groups and lone pairs and use VSEPR theory to determine the shape of the following molecules or ions as tetrahedral, trigonal pyramidal, or bent.
Step 3 Use the atoms bonded to the central atom to determine the molecular shape.
A. PF3 With three bonds and one lone pair, the shape is trigonal planar.
B. H2S With two bonds and two lone pairs, the shape is bent.
C. CCl4 With four bonds the shape is tetrahedral.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

75. Nonpolar Molecules Nonpolar molecules
such as H2, Cl2, and O2 are nonpolar because they contain nonpolar bonds
with polar bonds such as CO2 can be nonpolar if the polar bonds cancel each other in a symmetrical arrangement
dipoles cancel out, which makes the molecule nonpolar
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

76. Polar Molecules Polar molecules such as HCl are polar
because one end of the molecule is more negatively charged than the other
when polar bonds in the molecule do not cancel each other
because the electrons are shared unequally in the polar covalent bond
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

77. Polar Molecules In polar molecules
with three or more atoms, the shape of the molecule determines whether the dipoles cancel or not
there are often lone pairs around the central atom
such as H2O, the dipoles do not cancel, making the molecule positive at one end and negative at the other end
such as H2O, there is a dipole on the central atom
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

78. Learning Check
Identify each of the following molecules as polar or nonpolar. Explain.
A. PBr3
B. HBr
C. CF4
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.