Chapter 1: Chemical Bonding

Aspartame (Nutrasweet)

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I. Electronic Configurations of the ElementsPeriodic Table Review: periods; principle quantum numbers s-block, p-block, d-block; groups s and p atomic orbitals rules for filling atomic orbitals core and valence electrons Question 1-1. From a periodic table, give the electron configuration and Lewis structure for the following atoms. Then click on the arrow to check your answers. C N O F Cl

Check Answer

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I. Electronic Configurations of the ElementsAnswer 1-1: Electron Configuration C [He]2s22p2 Lewis Symbol

CNO

N

[He]2s22p3

O

[He]2s22p4

F

[He]2s22p5

F Cl3

Cl

[Ne]2s22p5

II. Bonding and Molecular StructureA. Ionic, covalent, and polar bonds: electronegativityionic bonds: transfer of electrons

Na + Cl

Na

+ Cl

covalent bonds: sharing of electrons

H + Cl

H Cl

electronegativity, ': relative attraction for electrons in a bond - increases going up and to the right in the periodic table - Pauling electronegativity scale (arbitrary): Table 1.2

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II. Bonding and Molecular StructureA. Ionic, covalent, and polar bonds: electronegativityHH ' = 2.1 2.1 ClCl ' = 3.0 3.0 H+ H HCl ' = 2.1 3.0 (' = 0 equal sharing of electrons = nonpolar covalent bond nonmetal + nonmetal (' = 0.9 unequal sharing of electrons = polar covalent bond metal + nonmetal

Na+Cl ' = 0.9 3.0 generally:

(' = 2.1 transfer of electrons = ionic bond when (' < 1.9 covalent > 1.9 ionic

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Question 1-2. Use a periodic table or use the Pauling electronegativity values to classify each of the following compounds as non-polar covalent, polar covalent, or ionic. Click on the arrow to check your answers. F2

H2

HF

NaFCheck Answer

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Answer 1-2. Compare your answers:

F2

F

F

Non-polar covalent

H2

H HH H

Non-polar covalent

HF

H F

Polar covalent

NaF

Na+ F-

Ionic

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II. Bonding and Molecular StructureB. Drawing Lewis structures1. Count all the valence electrons; add one for each charge subtract one for each + charge 2. Draw single bonds between the atoms (the connectivity of the atoms is determined experimentally and is usually given in the problem). 3. Using the remaining valence electrons, place octets on all atoms (exception H), in order of decreasing electronegativity. 4. If atoms do not have octets, use lone pair electrons on adjacent atoms to form double or triple bonds to complete the octets. 5. Determine formal charges. 6. The better Lewis structure is the one: -with fewer formal charges -with more octets -with a charge on a more electronegative atom, and vice versa8

II. Bonding and Molecular StructureB. Drawing Lewis structures Question 1-3. Draw Lewis structures of the following.CCl4 CH2O C 2H 2 CH3OH CH3CHCH2Check Answer

HCN9

II. Bonding and Molecular StructureB. Drawing Lewis structures Answer 1-3. Draw Lewis structures of the following.Cl Cl C Cl ClO H C HH C C H

CCl4H H C H O H

CH2O

C2H2

H H H H C C C H H

H C NHCN10

CH3OH

CH3CHCH2

II. Bonding and Molecular StructureC. Formal charges(Use the silly, complex formula in the textbook, or use this easier method.) 1. Divide the electrons in each bond equally between the two atoms sharing them. 2. Count the number of electrons each atom now has and compare this number to its normal valence. -more electrons than normal valence negative formal charge -fewer electrons than normal valence positive formal charge Question 1-4. Draw the Lewis structures, then determine the formal charge on each atom in the following molecules or ions. Check your answer by clicking on the arrow. H3O+ CH3O CH3+ CO N 3Check Answer

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II. Bonding and Molecular StructureC. Formal chargesAnswer 1-4. Compare your answers.

H H O H O: 6 - 5 = +1

H H C O H C: 4 - 4 = 0 O: 6 - 7 = -11 2 3

H H C H C: 4 - 3 = +11 2 3

C O C: 4 - 5 = -1 O: 6 - 5 = +1

N N N N1: 5 - 5 = 0 N2: 5 - 4 = +1 N3: 5 - 7 = -2

or

N N N N1: 5 - 6 = -1 N2: 5 - 4 = +1 N3: 5 - 6 = -112

II. Bonding and Molecular StructureC. Formal chargesWhen two or more nonequivalent Lewis structures are possible, the better (more stable) one is the one with: 1. fewer formal charges 2. more octets 3. a charge on a more electronegative atom, or a + charge on a more electropositive atom In decreasing order of importance

Question 1-5. Draw the most stable Lewis structure for each of the following compounds. Check your answers by clicking on the arrow. COCl2 BF3 (CH3)2SO HOCNCheck Answer

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II. Bonding and Molecular StructureC. Formal chargesAnswer 1-4. The preferred Lewis structures are shown here. Note that formal charges for all atoms in the preferred Lewis structure are 0.O Cl C Cl

F F B F

F +1

not

F

B -1

F

H O H H C H S C H H

H O C N

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II. Bonding and Molecular StructureD. Structural formulas of organic compoundsstructural formulaH H H H H H C C C C C H CH3CH2CH2CH2CH3 H H H H H H H OH H H C C C C H H H H H H O H H C C H C H H CH3CH2CHCH3 OH CH3CH2CH(OH)CH3 O CH3CCH3 CH3COCH3 (CH3)2CO15

condensed formula

bond-line formula

OH

O

II. Bonding and Molecular StructureD. Structural formulas of organic compoundsQuestion 1-6. Draw the first two compounds in a bond-line formula. Draw the second two compounds in a condensed formula. Click on the arrow to check your answer.(CH3)3CCH2CH2CH(CH3)2CH3CH2C(CH3)2CH(OH)CH2CH2CH2Cl

OH

OH Br

Check Answer

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II. Bonding and Molecular StructureD. Structural formulas of organic compoundsAnswer 1-6. Draw the first two compounds in a bond-line formula. Draw the second two compounds in a condensed formula. Click on the arrow to check your answer.Cl OH(CH3)3CCH2CH2CH(CH3)2CH3CH2C(CH3)2CH(OH)CH2CH2CH2Cl

OHOH

(CH3)2CHCH2C(CH3)2CH(OH)CH(Br)CH3OH Br

H2C H2C

CH CH2

CH2 CH2

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II. Bonding and Molecular StructureE. Constitutional isomers -different atoms bonded to one another; different connectivityC4H10 H H H H H C C C C H H H H H H H H H C C C H H H H C H H C3H8O C C C O O C C C C O C C CH3CH2CH2OH OH CH3CH(OH)CH3 CH3CH2OCH3 O18

CH3CH2CH2CH3

CH3CHCH3 CH3 CH3CH(CH3)CH3 OH

II. Bonding and Molecular StructureE. Constitutional isomersQuestion 1-8. Draw all of the constitutional isomers for the following. Check your answer by clicking on the arrow. C4H9Cl

C3H6O

Check Answer

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II. Bonding and Molecular StructureE. Constitutional isomersAnswer 1-8. There are four constitutional isomers and five constitutional isomers, respectively. C4H9ClCl Cl Cl Cl

C3H6OO O H O O O

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II. Bonding and Molecular StructureF. Resonance structures -atomic positions (connectivity) the same, but different arrangement of electrons

delocalized electrons

HCO2

-

O H C O H C

O = H C O

O O -

neither of these accurately describes the formate ion actual species is an average of the two

1.5 bond order

greater number of equivalent resonance structures greater stability = resonance stabilization21

II. Bonding and Molecular StructureF. Resonance structures Question 1-8. Draw resonance forms for the following. Indicate whether the resonance forms are equivalent in energy. If not, indicate the major resonance contributor (most stable). Click on the arrow to check your answers.SCNCH2N2 CH3CO2-

Check Answer

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II. Bonding and Molecular StructureF. Resonance structures Answer 1-8. The major resonance forms are marked. Formal charge is indicated above the structure.0 0 -1 S C N -1 S 0 0 C N +1 0 -2 S C N

SCN-

More electronegative atom has negative charge.H H H C N N0 +1 -1

CH2N2

H C N N-1 +1 0

More electronegative atom has negative charge. CH3CO2-

H O H C H C O

H O H C H C O

equal in stability23

II. Bonding and Molecular StructureG. Molecular geometry: Question 1-9. Draw Lewis structures and determine molecular geometry for each of the molecules. Click on the arrow to check.formula C2H2 CH2O CH4 HCN NH3 H2OCheck Answer

e pair geometry

molecular geometry (angle)

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II. Bonding and Molecular StructureG. Molecular geometry: Answer 1-9. Draw Lewis structures and determine molecular geometry for each of the molecules. Click on the arrow to check.formula C2H2 CH2O CH4 HCN NH3 H2O LewisH CO H CH C H H H

e pair geometryH linearH

molecular geometry (angle) linear (180) trigonal planar (120) tetrahedral (109.5)

C

trigonal planar tetrahedral

H C N

linear tetrahedral tetrahedral

linear (180) trigonal pyramidal (107) bent (104.5)25

N H H H

O H H

II. Bonding and Molecular StructureH. Molecular polarity Question 1-10. Draw the Lewis structures, give the molecular geometry, and determine whether the following will be polar or non-polar. Click on the arrow to check your answers.

CCl4

CHCl3

CH2O

CO2

Check Answer

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II. Bonding and Molecular StructureH. Molecular polarity Answer 1-10. Draw the Lewis structures, give the molecular geometry, and determine whether the following will be polar or non-polar. Click on the arrow to check your answers.CCl4Cl Cl C Cl Cl

CHCl3Cl

H C Cl Cl

no net dipole: non-polar CH2OH O C H

net dipole: polar CO2O C O

net dipole: polar

no net dipole: non-polar27

III. Other Bonding TheoriesA. Molecular orbital theory: H2H + H p HH

Two electrons in W1s are lower energy than in the separate atoms covalent bond28

III. Other Bonding TheoriesB. Valence bond theory1. sp3 hybridization CH4 facts:H C H H H

tetrahedral, 4 equivalent bonds

C

2p 2shybrid a.o.s:

promote electron

hybridize

2p 2s H4H sp3 hybrid a.o.s

sp3

C(sp3) tetrahedral

C H H HW(sp3C + 1sH)

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III. Other Bonding TheoriesB. Valence bond theory1. sp3 hybridization

C H H C C H H H W(sp3C + sp3C) H

N lone pairs in sp3 a.o.s H C N H H H W(sp3C + sp3N) H

O

H C O H H W(sp3C + sp3O)

H

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III. Other Bonding TheoriesB. Valence bond theory2. sp2 hybridization trigonal planar = sp2 C2H4 facts: HC C H H1s

H

all six atoms lie in same plane

H

1s

H

1s 2p sp2

H Csp

H2p

1s

C2p

2

T bond

H H

C C

H H

overlap p orbitals

H H

C C

H H=

H C H C

H H double bond = 1 T bond + 1 W bond

W(sp2C + 1sH) W(sp2C + sp2C)

all atoms coplanar for p orbital overlap

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III. Other Bonding TheoriesB. Valence bond theory2. sp2 hybridization

C H H C C H H W(sp2C + sp2C) + T H H

O lone pairs in sp2 a.o.s

C O

W(sp2C + sp2O) + T

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III. Other Bonding TheoriesB. Valence bond theory3. sp hybridization C2H2 facts: H

C C H

linear = sp

H

1s

H2p sp

1s

C2p H

C

2p sp 2 T bonds

C C

H W(spC + 1sH)

H

C C

H = H

C

C

H

W(spC + spC)

triple bond = 2 T bonds + 1 W bond

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III. Other Bonding TheoriesB. Valence bond theory3. sp hybridization

N lone pair in sp a.o. H C N

W(spC + spN) + 2T

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III. Other Bonding TheoriesB. Valence bond theoryQuestion 1-11. What is the hybridization of each indicated atom in the following compound? Click on the arrow to check your answers.

CH3 OH C CH

HO17-ethynylestradiol (The Pill) Check Answer35

III. Other Bonding TheoriesB. Valence bond theoryAnswer 1-11. What is the hybridization of each indicated atom in the following compound? Click on the arrow to check your answers. sp3 sp3

CH3 OH C CHsp

HOsp3 sp2 17-ethynylestradiol (The Pill)36