1. Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
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2. Chapter 7: Covalent Bonds and Molecular Structure
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The Covalent Bond
Covalent Bond: A bond that results from the sharing of electrons between atoms.
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Copyright © 2008 Pearson Prentice Hall, Inc.

3. Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Copyright © 2008 Pearson Prentice Hall, Inc.

4. Strengths of Covalent Bonds
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Strengths of Covalent Bonds
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5. A Comparison of Ionic and Covalent Bonds
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
A Comparison of Ionic and Covalent Bonds
While covalent bonds are relatively strong, the intermolecular forces between molecules are weaker.
To contrast, the lattice energy must be overcome to separate the ions from each other in ionic compounds.
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Copyright © 2008 Pearson Prentice Hall, Inc.

6. Polar Covalent Bonds: Electronegativity
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Polar Covalent Bonds: Electronegativity
Electronegativity: The ability of an atom in a molecule to attract the shared electrons in a covalent bond.
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Copyright © 2008 Pearson Prentice Hall, Inc.

7. Polar Covalent Bonds: Electronegativity
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Polar Covalent Bonds: Electronegativity
NaCl
Cl2
HCl
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8. Polar Covalent Bonds: Electronegativity
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Polar Covalent Bonds: Electronegativity
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Copyright © 2008 Pearson Prentice Hall, Inc.

9. Electron-Dot Structures
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Electron-Dot Structures
Electron-Dot Structures (Lewis Structures): A representation of an atom’s valence electrons by using dots and indicates by the placement of dots how the valence electrons are distributed in the molecule.
Think of this section as an introduction. It is much easier to write electron-dot structures using the rules listed in the next section.
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10. Electron-Dot Structures
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Electron-Dot Structures
We have single, double, and triple bonds.
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Copyright © 2008 Pearson Prentice Hall, Inc.

11. Electron-Dot Structures of Polyatomic Molecules
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Electron-Dot Structures of Polyatomic Molecules
Step 1: Valence Electrons
Count the total number of valence electrons for all atoms in the molecule.
Add one additional electron for each negative charge in an anion or subtract one for each positive charge in a cation.
The rules seem arbitrary to students.
They have been developed in order to get to a finished structure.
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Copyright © 2008 Pearson Prentice Hall, Inc.

12. Electron-Dot Structures of Polyatomic Molecules
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Electron-Dot Structures of Polyatomic Molecules
Step 2: Connect Atoms
Draw lines to represent bonds between atoms.
For hydrogen and second row atoms, use the number of bonds listed below.
For third row and greater atoms, they may have more bonds than predicted by the octet rule.
The least electronegative atom is usually the central atom.
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Copyright © 2008 Pearson Prentice Hall, Inc.

13. Electron-Dot Structures of Polyatomic Molecules
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Electron-Dot Structures of Polyatomic Molecules
Step 3: Assign Electrons to the Terminal Atoms
Subtract the number of electrons used for bonding in the previous step from the total number determined in step 1.
Complete each terminal atom’s octet (except for hydrogen).
Step 4: Assign Electrons to the Central Atom
If unassigned electrons remain after step 3, place them on the central atom.
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14. Electron-Dot Structures of Polyatomic Molecules
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Electron-Dot Structures of Polyatomic Molecules
Step 5: Multiple Bonds
If no unassigned electrons remain after step 3 but the central atom does not yet have an octet, use one or more lone pairs of electrons from a neighboring atom to form a multiple bond (either a double or a triple).
It’s important to follow the rules as developed. Otherwise, students have a difficult time knowing when to do multiple bonding.
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Copyright © 2008 Pearson Prentice Hall, Inc.

15. Electron-Dot Structures of Polyatomic Molecules
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Electron-Dot Structures of Polyatomic Molecules
Draw an electron-dot structure for H2O.
Step 1:
2(1) + 6 = 8 valence electrons H O H O
Step 2:
Step 4:
Step 2: The positioning of the terminal atoms about the central is not critical as long as they simply surround the central atom.
Step 3: The terminal atom is hydrogen.
Step 5: The central atom has an octet so no multiple bonding.
bonding pair of electrons
lone pair of electrons
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Copyright © 2008 Pearson Prentice Hall, Inc.

16. Electron-Dot Structures of Polyatomic Molecules
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Electron-Dot Structures of Polyatomic Molecules
Draw an electron-dot structure for CCl4.
Step 1:
4 + 4(7) = 32 valence electrons Cl C Cl C
Step 2:
Step 3:
Step 4: The central atom already has an octet.
Step 5: The central atom has an octet so no multiple bonding.
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Copyright © 2008 Pearson Prentice Hall, Inc.

17. Electron-Dot Structures of Polyatomic Molecules
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Electron-Dot Structures of Polyatomic Molecules
Draw an electron-dot structure for H3O1+.
Step 1:
3(1) = 8 valence electrons 1+ H O H O
Step 2:
Step 4:
Step 1: Subtract 1 from the total number of valence because of the 1+ charge.
Step 3: The terminal atoms are hydrogen.
Step 5: The central atom has an octet so no multiple bonding.
Don’t forget to show the charge on the ion!
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Copyright © 2008 Pearson Prentice Hall, Inc.

18. Electron-Dot Structures of Polyatomic Molecules
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Electron-Dot Structures of Polyatomic Molecules
Draw an electron-dot structure for CH2O.
Step 1:
4 + 2(1) + 6 = 12 valence electrons H C O H C O
Step 2:
Step 5:
Step 2: The least electronegative atom is the central one (hydrogen can’t be the central atom).
Step 3: Two of the terminal atoms are hydrogen.
Step 4: There are no remaining electrons to place on the central atom.
Step 5: “Borrow” a pair from oxygen to complete the central atom’s octet. H C O H C O
Step 3:
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Copyright © 2008 Pearson Prentice Hall, Inc.

19. Electron-Dot Structures of Polyatomic Molecules
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Electron-Dot Structures of Polyatomic Molecules
Draw an electron-dot structure for SF6.
Step 1:
6 + 4(7) = 34 valence electrons F S F S
Step 2:
Step 3:
Step 2: The central atom is in row 3 so there can be more than 8 electrons.
Step 4: There are no remaining electrons.
Step 5: The central atom has at least 8 electrons so no multiple bonding.
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Copyright © 2008 Pearson Prentice Hall, Inc.

20. Electron-Dot Structures of Polyatomic Molecules
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Electron-Dot Structures of Polyatomic Molecules
Draw an electron-dot structure for ICl3.
Step 1:
7 + 3(7) = 28 valence electrons Cl I Cl Cl Cl
Step 2:
Step 4: I
Step 4: The remaining electrons go on the central atom.
Step 5: The central atom has at least 8 electrons so no multiple bonding. Cl I
Step 3:
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Copyright © 2008 Pearson Prentice Hall, Inc.

21. Electron-Dot Structures and Resonance
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Electron-Dot Structures and Resonance
Draw an electron-dot structure for O3.
Step 1:
3(6) = 18 valence electrons O
Step 2: O
Step 4:
Step 4: There is only 1 more pair of electrons. Thus, the central oxygen only has 3 pairs of electrons (less than an octet).
Step 5: There is a choice to be made. If all that is desired is the electron-dot structure, then either of the 2 terminal oxygen atoms could have been chosen. O O
Step 3:
Step 5:
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Copyright © 2008 Pearson Prentice Hall, Inc.

22. Electron-Dot Structures and Resonance
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Electron-Dot Structures and Resonance
Move a lone pair from this oxygen?
Step 4: O
Or, move a lone pair from this oxygen?
Either electron-dot structure suggests that ozone has a double and a single bond. A bond analysis actually shows one type of bond and it’s neither a single nor a double bond. A resonance hybrid attempts to overcome this shortcoming of electron-dot structures.
At this stage, we usually just take this simplified look at resonance structures. Organic chemistry, for example, takes a much deeper look at resonance. O O
Resonance
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Copyright © 2008 Pearson Prentice Hall, Inc.

23. Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Formal Charges
Formal
Charge
# of
valence e-
in free atom - 2 1
nonbonding e-
bonding =
Calculate the formal charge on each atom in O3. O
The sum of the formal charges will be equal to the overall charge of the molecule or ion. 1 2 1 2 1 2
(4) - 4 = 0
(6) - 2 = +1
(2) - 6 = -1
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Copyright © 2008 Pearson Prentice Hall, Inc.

24. Molecular Shapes: the VSEPR Model
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Molecular Shapes: the VSEPR Model
VSEPR: Valence-Shell Electron-Pair Repulsion model
Electrons in bonds and in lone pairs can be thought of as “charge clouds” that repel one another and stay as far apart as possible, this causing molecules to assume specific shapes.
Working from an electron-dot structure, count the number of “charge clouds,” and then determine the molecular shape.
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Copyright © 2008 Pearson Prentice Hall, Inc.

25. Molecular Shapes: the VSEPR Model
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Molecular Shapes: the VSEPR Model
Two Charge Clouds
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Copyright © 2008 Pearson Prentice Hall, Inc.

26. Molecular Shapes: the VSEPR Model
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Molecular Shapes: the VSEPR Model
Three Charge Clouds
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Copyright © 2008 Pearson Prentice Hall, Inc.

27. Molecular Shapes: the VSEPR Model
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Molecular Shapes: the VSEPR Model
Four Charge Clouds
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Copyright © 2008 Pearson Prentice Hall, Inc.

28. Molecular Shapes: the VSEPR Model
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Molecular Shapes: the VSEPR Model
Four Charge Clouds
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Copyright © 2008 Pearson Prentice Hall, Inc.

29. Molecular Shapes: the VSEPR Model
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Molecular Shapes: the VSEPR Model
Five Charge Clouds
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Copyright © 2008 Pearson Prentice Hall, Inc.

30. Molecular Shapes: the VSEPR Model
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Molecular Shapes: the VSEPR Model
Five Charge Clouds
Copyright © 2008 Pearson Prentice Hall, Inc.
Copyright © 2008 Pearson Prentice Hall, Inc.

31. Molecular Shapes: the VSEPR Model
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Molecular Shapes: the VSEPR Model
Six Charge Clouds
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Copyright © 2008 Pearson Prentice Hall, Inc.

32. Molecular Shapes: the VSEPR Model
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Molecular Shapes: the VSEPR Model
Six Charge Clouds
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Copyright © 2008 Pearson Prentice Hall, Inc.

33. Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Copyright © 2008 Pearson Prentice Hall, Inc.

34. Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Copyright © 2008 Pearson Prentice Hall, Inc.

35. Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Copyright © 2008 Pearson Prentice Hall, Inc.

36. Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Valence Bond Theory
Valence Bond Theory: A quantum mechanical model which shows how electron pairs are shared in a covalent bond.
sigma (s) bonds
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Copyright © 2008 Pearson Prentice Hall, Inc.

37. Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Valence Bond Theory
Valence Bond Theory: A quantum mechanical model which shows how electron pairs are shared in a covalent bond.
Covalent bonds are formed by overlap of atomic orbitals, each of which contains one electron of opposite spin.
Each of the bonded atoms maintains its own atomic orbitals, but the electron pair in the overlapping orbitals is shared by both atoms.
The greater the amount of overlap, the stronger the bond.
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Copyright © 2008 Pearson Prentice Hall, Inc.

38. Hybridization and sp3 Hybrid Orbitals
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Hybridization and sp3 Hybrid Orbitals
How can the bonding in CH4 be explained?
4 valence electrons
2 unpaired electrons
How can carbon have 4 bonds if there are only 2 unpaired valence electrons?
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Copyright © 2008 Pearson Prentice Hall, Inc.

39. Hybridization and sp3 Hybrid Orbitals
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Hybridization and sp3 Hybrid Orbitals
How can the bonding in CH4 be explained?
4 valence electrons
4 unpaired electrons
Promotion of 1 electron allows for 4 unpaired valence electrons.
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Copyright © 2008 Pearson Prentice Hall, Inc.

40. Hybridization and sp3 Hybrid Orbitals
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Hybridization and sp3 Hybrid Orbitals
How can the bonding in CH4 be explained?
4 nonequivalent orbitals
The 4 bonds in CH4 must be equivalent (tetrahedral distribution).
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Copyright © 2008 Pearson Prentice Hall, Inc.

41. Hybridization and sp3 Hybrid Orbitals
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Hybridization and sp3 Hybrid Orbitals
How can the bonding in CH4 be explained?
4 equivalent orbitals
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Copyright © 2008 Pearson Prentice Hall, Inc.

42. Hybridization and sp3 Hybrid Orbitals
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Hybridization and sp3 Hybrid Orbitals
Copyright © 2008 Pearson Prentice Hall, Inc.
Copyright © 2008 Pearson Prentice Hall, Inc.

43. Hybridization and sp3 Hybrid Orbitals
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Hybridization and sp3 Hybrid Orbitals
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Copyright © 2008 Pearson Prentice Hall, Inc.

44. Other Kinds of Hybrid Orbitals
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Other Kinds of Hybrid Orbitals
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Copyright © 2008 Pearson Prentice Hall, Inc.

45. Other Kinds of Hybrid Orbitals
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Other Kinds of Hybrid Orbitals
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Copyright © 2008 Pearson Prentice Hall, Inc.

46. Other Kinds of Hybrid Orbitals
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Other Kinds of Hybrid Orbitals
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Copyright © 2008 Pearson Prentice Hall, Inc.

47. Other Kinds of Hybrid Orbitals
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Other Kinds of Hybrid Orbitals
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Copyright © 2008 Pearson Prentice Hall, Inc.

48. Other Kinds of Hybrid Orbitals
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Other Kinds of Hybrid Orbitals
Summary.
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Copyright © 2008 Pearson Prentice Hall, Inc.

49. Molecular Orbital Theory: The Hydrogen Molecule
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Molecular Orbital Theory: The Hydrogen Molecule
Atomic Orbital: A wave function whose square gives the probability of finding an electron within a given region of space in an atom.
Molecular Orbital: A wave function whose square gives the probability of finding an electron within a given region of space in a molecule.
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Copyright © 2008 Pearson Prentice Hall, Inc.

50. Molecular Orbital Theory: The Hydrogen Molecule
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Molecular Orbital Theory: The Hydrogen Molecule
s bonding orbital
lower in energy
s* antibonding orbital
higher in energy
Bond Order =
(# Bonding e- - # Antibonding e-) 2
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Copyright © 2008 Pearson Prentice Hall, Inc.

51. Molecular Orbital Theory: The Hydrogen Molecule
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Molecular Orbital Theory: The Hydrogen Molecule
= 1 2
2 - 0
Bond Order =
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Copyright © 2008 Pearson Prentice Hall, Inc.

52. Molecular Orbital Theory: The Hydrogen Molecule
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Molecular Orbital Theory: The Hydrogen Molecule = 2 1
2 - 1
= 0 2
2 - 2
Bond Order:
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Copyright © 2008 Pearson Prentice Hall, Inc.

53. Molecular Orbital Theory: Other Diatomic Molecules
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Molecular Orbital Theory: Other Diatomic Molecules O2 O
Diamagnetic: All electrons are spin-paired. It is weekly repelled by magnetic fields.
Paramagnetic: There is at least one unpaired electron. It is weakly attracted by magnetic fields.
Pictures of liquid oxygen attracted to the poles of an electromagnet are nice to show at this point.
Oxygen, O2, is predicted to be diamagnetic by electron-dot structures and valence bond theory.
However, it is known to be paramagnetic.
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Copyright © 2008 Pearson Prentice Hall, Inc.

54. Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Copyright © 2008 Pearson Prentice Hall, Inc.

55. Molecular Orbital Theory: Other Diatomic Molecules
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Molecular Orbital Theory: Other Diatomic Molecules
Copyright © 2008 Pearson Prentice Hall, Inc.
Copyright © 2008 Pearson Prentice Hall, Inc.

56. Molecular Orbital Theory: Other Diatomic Molecules
Chapter 7: Covalent Bonds and Molecular Structure
4/28/2019
Molecular Orbital Theory: Other Diatomic Molecules
Copyright © 2008 Pearson Prentice Hall, Inc.