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hapter 5. Covalent Compounds (Molecular Compounds) NaCl (ionic compound) heat Na + + Cl - (gas) H 2 O (liquid) Heat H 2 O molecules (gas) NH 3 NH 3 (molecules) etc. lecular formula tells the # of atoms of each elemen molecule of the compound C 2 F 4 C 2 H 6 O 1

Chapter 5. Covalent Compounds (Molecular Compounds)

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Chapter 5. Covalent Compounds (Molecular Compounds). heat. NaCl (ionic compound). Na + + Cl - (gas). Heat. H 2 O (liquid). H 2 O molecules (gas). NH 3. NH 3 (molecules). etc. A molecular formula tells the # of atoms of each element in a molecule of the compound. - PowerPoint PPT Presentation

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Page 1: Chapter 5.  Covalent Compounds (Molecular Compounds)

Chapter 5. Covalent Compounds (Molecular Compounds)

NaCl (ionic compound) heat

Na+ + Cl- (gas)

H2O (liquid) Heat

H2O molecules (gas)

NH3 NH3 (molecules)

etc.

A molecular formula tells the # of atoms of each element in a molecule of the compound

C2F4 C2H6O

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Page 2: Chapter 5.  Covalent Compounds (Molecular Compounds)

A. Covalent bonds

Example H + H H2

H H Sharing of electrons H H

or H H

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Page 3: Chapter 5.  Covalent Compounds (Molecular Compounds)

H + Cl HCl

H Cl Lewis structureClHCl

Octet rule

Draw the Lewis structures of

H2O

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Page 4: Chapter 5.  Covalent Compounds (Molecular Compounds)

NH3

CH4

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Page 5: Chapter 5.  Covalent Compounds (Molecular Compounds)

Draw Lewis structures for the following compounds

Consider O2

Consider N2

CH2O

C2H4

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Page 6: Chapter 5.  Covalent Compounds (Molecular Compounds)

B. Coordinate Covalent Bonds (less common)

B

H

H

H

B

H

H

H

N

H

H

HB

H

H

H

= N

H

H

HB

H

H

H

Electron deficient compound

Coordinate covalent bond

BH3

NH3

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Page 7: Chapter 5.  Covalent Compounds (Molecular Compounds)

Draw Lewis structure for each of the following molecular formulas in the most stable form (by pure sharing of electrons).

a) PCl3 b) C2F6

c) CH2O2 d) CH3N

e) C2H2Cl2 f) N2O2

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Page 8: Chapter 5.  Covalent Compounds (Molecular Compounds)

Common elements in covalent compounds: C, O, N

C C C C

N N N

O O

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Page 9: Chapter 5.  Covalent Compounds (Molecular Compounds)

For compounds containing C, H, O, N (the big 4), and F, try this

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Page 10: Chapter 5.  Covalent Compounds (Molecular Compounds)

HCN

CO2

C3H4

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Page 11: Chapter 5.  Covalent Compounds (Molecular Compounds)

C. Compounds not following the Octet Rule

NO

PCl5

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Page 12: Chapter 5.  Covalent Compounds (Molecular Compounds)

E. Lewis structures of Polyatomic ions or molecules with a central atom.

1. Calculate the total number of valence electrons.2 Draw a single bond between the central atom and each of the surrounding atoms.

3. Add nonbonding electrons to surrounding atoms such that each has an octet of electrons (2 on H).4. Place the remaining electrons on the central atom.5. If the central atom does not have octet of electrons, use one or two pairs of nonbonding e’s from the surround atoms to form double or triple bonds with the central atom.6. Check the total number of electrons.

NO2-

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Page 13: Chapter 5.  Covalent Compounds (Molecular Compounds)

Resonance

ON

O ON

O

Resonance structuresor resonance contributors

NO2-

The real molecule or ion is a resonance hybrid of the resonance structures.Each resonance structure is less stable than the resonance hybrid.

- -

O N O-

??

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Page 14: Chapter 5.  Covalent Compounds (Molecular Compounds)

Neutral molecules with a central atom

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Page 15: Chapter 5.  Covalent Compounds (Molecular Compounds)

Examples:

NO3-

SO32-

Polyatomic ions

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Page 16: Chapter 5.  Covalent Compounds (Molecular Compounds)

Lewis dot structures of ionic compounds:

K2SO3

Ca(NO3)2

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Page 17: Chapter 5.  Covalent Compounds (Molecular Compounds)

F. Electronegativity (EN)

Electronegativity of an element = the relative tendency of its atoms to attract the bonding electron pair.

H Cl H Clor

EN of Cl > EN of H

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Page 18: Chapter 5.  Covalent Compounds (Molecular Compounds)

Fig.5.11 Pauling Electronegativity Values

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Page 19: Chapter 5.  Covalent Compounds (Molecular Compounds)

-

H Cl H Cl

G. Polar covalent bond

Polar covalent bond

Figure 5.12:

(a) (b) Nonpolar and Polar Covalent Bond

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Page 20: Chapter 5.  Covalent Compounds (Molecular Compounds)

The relative E.N. determines the bond type

Examples:

Bond Type Electronegativity Difference

Nonpolar Covalent 0.4 or less

Polar Covalent Greater than 0.4 to 1.5

Polar CovalentBetween 1.5 and 2.0 (between nonmetals)

IonicBetween 1.5 and 2.0 (metal and nonmetal)

Ionic Greater than 2.0

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Page 21: Chapter 5.  Covalent Compounds (Molecular Compounds)

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ExerciseArrange the following bonds from most to least polar: 

a) N-F O-F C-F

b) C-F N-O Si-F

c) Cl-Cl B-Cl S-Cl

Page 22: Chapter 5.  Covalent Compounds (Molecular Compounds)

H. Molecular Geometry Valence shell electron pair repulsion (VSEPR) theory

CH4 H C

H

H

H

All 4 bonds are equivalent

H

C

HHH

H

C

HHH

Tetrahedral

Cs p p p

sp3 sp3 sp3 sp3

Four sp3 hybrid orbits

109.5o

Lewis structure

hybr

idize

Electron pair arrangement

Molecular geometry

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Page 23: Chapter 5.  Covalent Compounds (Molecular Compounds)

o180o120o 109.5o

hybrid orbitals: sp sp2 sp3

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Page 24: Chapter 5.  Covalent Compounds (Molecular Compounds)

NH3H N H

H

N

HHH

Electron pair arrangement: tetrahedralMolecular geometry: trigonal pyramidal

sp3

H2O H O H O

H

H

sp3

Electron pair arrangement: tetrahedralMolecular geometry: angular

Lewis structure

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Page 25: Chapter 5.  Covalent Compounds (Molecular Compounds)

BH3

Lewis structure

H B H

H

H

B

H H

s p p pB

s p p p

sp2 sp2 sp2

Three sp2 hybrid orbitals

sp2

Trigonal planar

Electron pair arrangement: trigonal planarMolecular geometry: trigonal planar 25

Page 26: Chapter 5.  Covalent Compounds (Molecular Compounds)

SO2 O S OS

O O

Electron pair arrangement: trigonal planarMolecular geometry: bent

BeH2

s ps p

sp2

Two sp hybrid orbitalsH Be H sp

Electron pair arrangement: linearMolecular geometry: linear

sp sp

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Page 27: Chapter 5.  Covalent Compounds (Molecular Compounds)

hybrid orbitals: sp sp2 sp3

o180o

120o 109o

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Page 28: Chapter 5.  Covalent Compounds (Molecular Compounds)

The Shape (Geometry) of Molecules

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Page 29: Chapter 5.  Covalent Compounds (Molecular Compounds)

Summary# of groups electron pair makeup molecular hybridof electrons (density) of e- groups geometry orbitalsaround arrangementcentral atom 4 tetrahedral 4 bonding tetrahedral

3 bonding trigonal1 nonbonding pyramidal sp3

2 bonding angular2 nonbonding (bent)

3 Trigonal 3 bonding Trigonal planar planar sp2

2 bonding Angular1 nonbonding

2 Linear 2 bonding Linear sp29

Page 30: Chapter 5.  Covalent Compounds (Molecular Compounds)

Examples:

HCN

Electron pairarrangement

Moleculargeometry

Hybirdorbitals

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Page 31: Chapter 5.  Covalent Compounds (Molecular Compounds)

I. Polarity of Molecules

H Cl One polar bondPolar molecule

O

H Hnet

O C O

Polar molecule

Non polar moleculeThe 2 polar bonds cancel each other

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Page 32: Chapter 5.  Covalent Compounds (Molecular Compounds)

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Page 33: Chapter 5.  Covalent Compounds (Molecular Compounds)

Summary: • Draw the Lewis structure• If all electron groups around the central atom are connected to the same atom – nonplar otherwise - polar

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Page 34: Chapter 5.  Covalent Compounds (Molecular Compounds)

J. Naming of binary molecular compounds

mono- 1di- 2tri- 3tetra- 4penta- 5hexa- 6hepta- 7octa- 8ennea-(neno) 9deca- 10

P2O5 diphosphorus pentaoxide

N2O4 dinitrogen tetraoxide

CO2

SO2

NO

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