1. Properties of Molecular Substances
Low melting & boiling points
Low heats of fusion & vaporization
High vapor pressure
May be soft, as wax
May be crystalline, as sugar
(weak lattice, based on dipole-dipole or H bonding)
Molecules are neutral. NEVER conduct.
Properties of Molecular Substances

2. Breaking 
 Making
Breaking a bond is endothermic.
Making a bond is exothermic.
Breaking a bond is endothermic. Making a bond is exothermic.
Describe changes in chemical potential energy that accompany bond formation or bond breaking.

3. Describe the relationship between stability & potential energy
As PE , stability .
As PE , stability .
Describe the relationship between stability & potential energy

4. H + H  H2 + energy
Exothermic
- energy term is on product side
- bond formation releases energy
Does the above equation represent an endothermic or exothermic process? How do you know?

5. H2 + energy  H + H
Endothermic
- energy term is on reactant side
- bond breaking absorbs energy
Does the above equation represent an endothermic or exothermic process? How do you know?

6. To achieve the electron configuration of the nearest noble gas!
Why do atoms form bonds?

7. Covalent Bonds
Electrons are shared

8. How do you identify a covalent formula?
All Nonmetals in formula
How do you identify a covalent formula?

9. Covalent bonds result from …
The simultaneous attraction of electrons and two different nuclei.
Covalent bonds result from …

10. What kinds of formulas do molecular substances have?
Molecular, which give exact composition of molecule
Empirical, which give lowest whole number ratio of atoms in molecule
Sometimes they are the same.
Otherwise, molecular is a whole number multiple of empirical
C6H6 CH
H2O
What kinds of formulas do molecular substances have?

11. Structural Formula Shows which elements & how many atoms of each.
Shows connectivity or how atoms are linked
Shows type of bond – single, double or triple
H-O-H
O=C=O
O-N=O
Structural Formula

12. Lewis Diagram Shows type & number of atoms. Shows connectivity
Shows type of bonds
Shows all nonbonding valence electrons, in addition to the bonding valence electrons
Bonding electrons are in between two atoms!
Lewis Diagram

13. One electron pair or Two electrons Shared between atoms
Represented by 2 dots or 1 dash between atoms
Single Bond

14. Two electron pairs or Four electrons Shared between atoms
Represented by 4 dots or 2 dashes between atoms
Double Bond

15. Three electron pairs or Six electrons Shared between atoms
Represented by 6 dots or 3 dashes between atoms
Triple Bond

16. Energy change that occurs when a bond is formed between two atoms.
Symbol = D0
Bond Energy

17. Triple > Double > Single
As the number of electrons shared between 2 atoms increases, the attractive interactions increase, & the bond energy increases.
Triple > Double > Single
Bond Energy

18. Distance between two bonded nuclei.
The more shared electrons between 2 nuclei, the greater the attractive interactions, the shorter the bond length.
Bond Length

19. All single bonds are sigma bonds.
Overlap of two orbitals occurs on the line directly connecting the two nuclei.
All single bonds are sigma bonds.
 Bond

20. Overlap of two orbitals occurs above and below the line that directly connects the two nuclei.
Double bonds consist of one  & one  bond.
Triple bonds consist of one & two  bonds.
 Bond

21. Procedure for writing a Lewis structure for a molecular substance
Total up the valence electrons from all the atoms in the molecule.
Draw the skeleton, including a single bond between every atom.
Compare numbers:
# of electrons needed for each atom in the skeleton to have an octet/duet
# of electrons available after drawing skeleton
Distribute electrons
Verify by performing two validity checks
Procedure for writing a Lewis structure for a molecular substance

22. Lewis Diagram of H2 Total # of valence electrons = 2 Skeleton: H – H
Compare: 0 electrons needed & 0 electrons available
No electrons to distribute
Verify.
Lewis Diagram of H2

23. Lewis Diagram of Cl2 # of valence electrons = 14 Skeleton: Cl – Cl
Compare: Need 12, Have 12
Distribute
Verify
Lewis Diagram of Cl2

24. Bonding vs. Nonbonding electron pairs
Bonding electrons are located BETWEEN two atoms.
Nonbonding electrons are located on one atom only.
Bonding vs. Nonbonding electron pairs

25. Lewis Diagram of O2 # of valence electrons = 12 Skeleton: O - O
A) Compare: Need 12, Have 10, deficient by 2, add 1 bond
B) O  O. Compare: Need 8, have 8.
Distribute
Verify
Lewis Diagram of O2

26. Lewis Diagram of N2 # of valence electrons = 10 Skeleton: N – N
A) Compare: Need 12, Have 8, deficient by 4, add 2 bonds
B) N  N. Compare: Need 4, have 4.
Distribute
Verify
Lewis Diagram of N2

27. Lewis Diagram of H2O # of valence electrons = 8 Skeleton: H – O – H
Compare: Need 4, Have 4
Distribute
Verify
Lewis Diagram of H2O

28. Lewis Diagram of NH3 - # of valence electrons = 8 Skeleton: H
Compare: Need 2, Have 2
Distribute
Verify H
H – N – H -
Lewis Diagram of NH3

29. - - Lewis Diagram of CH4 # of valence electrons = 8
Skeleton: H – C – H
Compare: Need 0, Have 0
Distribute (nothing)
Verify H - -
Lewis Diagram of CH4

30. - - Lewis Diagram of CCl4 # of valence electrons = 32 Cl
Skeleton: Cl – C – Cl
Compare: Need 24, Have 24
Distribute
Verify Cl - -
Lewis Diagram of CCl4

31. - - - - Lewis Diagram of C2H4 # of valence electrons = 12
Skeleton: H – C – C - H
A) Compare: Need 4, Have 2. Add 1 bond.
Distribute (nothing)
Verify
H H - - -
H H
B) Compare: Need 0, Have 0 -
H – C  C - H
Lewis Diagram of C2H4

32. Lewis Diagram of C2H2 # of valence electrons = 10
Skeleton: H – C – C - H
A) Compare: Need 8, Have 4. Add 2 bonds.
B) Compare: Need 0, Have 0
Distribute (nothing)
Verify
H – C  C - H
Lewis Diagram of C2H2

33. Lewis Diagram of CO2 # of valence electrons = 16 Skeleton: O – C - O
A) Compare: Need 16, Have 12, deficient by 4, add 2 bonds
B) O  C  O. Compare: Need 8, have 8.
Distribute
Verify
Lewis Diagram of CO2

34. What are Resonance Structures?
Sometimes, more than one valid Lewis structure can be written for a molecule. For CO2:
<-->
<-->
What are Resonance Structures?

35. Resonance Structures The atoms are in the same location.
The electrons are distributed differently.
Resonance Structures

36. What are the three general ways the octet rule breaks down?
Molecules with an odd # of electrons can never satisfy the octet rule for all their atoms. (NO, NO2, ClO2)
Some molecules have an atom with less than an octet. (BF3, BeH2)
Some molecules have an atom with more than an octet. (PCl5, SF6)
What are the three general ways the octet rule breaks down?

37. Molecules with odd # of electrons
Consider NO = 11 valence electrons
Skeleton: N – O
A) Compare: the N needs 6 & the O needs 6 for a total of 12. Have only 9 available. Add one bond.
B) N = O now each atom needs 4 for a total of 8. Have only 7 available.
Distribute: :N = O:
Verify
The N atom has only 7 valence e-

38. Molecules with odd # of electrons
Consider NO (6) = 17 electrons
Skeleton: O – N – O
A) Compare: each O needs 6 & N needs 4. Need 16 total. Have 13 available. Add 1 bond.
B) O = N – O Compare: Need or 12 electrons. Have 11 available.
Distribute: :O = N – O:
Verify ..
The N atom has only 7 e-

39. Molecules with odd # of electrons
Consider ClO (6) = 19 valence e-
Skeleton is O – Cl – O
Compare: Need = 16 e-
Have: 19 – 4 = 15. Deficient by 1 e-. Can’t fix.
Distribute :O – Cl – O:
Verify
The Cl atom has only 7 valence e- !

40. Molecules with atoms that have less than an octet
Occurs in molecules with Be and B. Be likes to have 4 valence electrons in molecules. B likes to have 6 valence electrons in molecules.

41. Molecules with atoms that contain more than an octet
Only the central atom can have more than an octet.
And only if it belongs in rows 3-7 of the PT.
Consider PF (7) = 40 valence e-.
Since P is in row 3 it has empty d orbitals available which can be used for bonding.
Skeleton: F
F P
Distribute the remaining 30 e- by placing 6 e- on each of the 5 F atoms.
The P has > than an octet.

42. A group of covalently bonded atoms that has gained or lost electrons and hence acquired a charge
Polyatomic Ions

43. Lewis Diagrams of Polyatomic Ions
When calculating the total # of valence electrons, you must adjust for the charge of the ion.
Total up the electrons contributed from each atom.
Add 1 electron for each negative charge. Or
Subtract 1 electron for each positive charge.

44. - Lewis Diagram of NH4+1 # of valence electrons = 9 – 1 = 8 +1 H
Skeleton:
Compare: Need 0, Have 0
Distribute (nothing)
Verify
H – N – H H - +1
Lewis Diagram of NH4+1

45. Lewis Diagram of OH-1 # of valence electrons = 6 + 1 + 1 = 8
Skeleton: [O – H]-1
Compare: Need 6, Have 6
Distribute: [:O - H]-1
Verify
: :
Lewis Diagram of OH-1

46. Determining Molecular Shape from the Lewis Structure
Count up the number of electron domains on the central atom.
Single, double, & triple bonds each count as ONE domain.
Lone electron pairs (or even a lone singleton) counts as ONE domain.
Count up the number of atoms that are bonded to the central atom.
Compare these two numbers to get the shape.

47. Shapes on the Regents Exam
# of electron domains on central atom
# of atoms bonded TO the central atom
Shape
Example 2
Linear
CO2 4
Tetrahedral, 109
CH4 3
Trigonal Pyramid, 107
NH3
Bent, 105
H2O

48. Additional Shapes: Know *reds
# of electron domains on central atom
# of atoms bonded TO the central atom
Shape
Example 3
*Trigonal Planar, bond angle = 120
BF3, BH3, SO3 5
*Trigonal Bipyramid
PF5 4
See-Saw
T-Shape 2
Linear 6
*Octahedral
SF6
Square Pyramid
Square Planar

49. Tetrahedral Molecule

50. Trigonal Pyramidal Molecule

51. Bent Molecule

52. Shape of CH4 Inspect central atom in Lewis diagram: Central atom has
- 4 electron domains
- 4 bonded atoms
Shape is tetrahedral
with 109 bond angles

53. Shape of NH3 Inspect central atom in Lewis diagram: Central atom has
- 4 electron domains
- 3 bonded atoms
Shape is trigonal pyramid with 107 bond angle
Why isn’t the bond angle 109?
Because the lone pair on the N atom spreads out & squeezes the bonding pairs together.

54. Shape of H2O Inspect central atom in Lewis Diagram: Central atom has
- 4 electron domains
- 2 atoms bonded to it
Shape is Bent with a 105 angle
Why isn’t the bond angle 109?
Because the two lone pairs on the O spread out more than the 2 bonding pairs and squeeze the bonding pairs together.

55. Shape of BF3 Inspect central atom in Lewis Diagram: Central atom has
Recall: B is an exception to the octet rule!
Inspect central atom in Lewis Diagram:
Central atom has
- 3 electron domains
- 3 atoms bonded to it
Shape is Trigonal Planar with a 120 angle or

56. Shape of BeF2 Inspect central atom in Lewis Diagram: Central atom has
Recall: Be is an exception to the octet rule!
Inspect central atom in Lewis Diagram:
Central atom has
- 2 electron domains
- 2 atoms bonded to it
Shape is Linear with a 180 angle

57. Shape of SO2 Inspect central atom in Lewis Diagram: Central atom has
- 3 electron domains
- 2 atoms bonded to it
Shape is Bent with a 120 angle

58. Shape of PF5 Inspect central atom in Lewis Diagram: Central atom has
- 5 electron domains
- 5 atoms bonded to it
Shape is Trigonal Bipyramid F
F P
The P is allowed to have an “expanded octet” because it has empty 3d orbitals that can hold valence electrons.

59. PF5 Two kinds of F atoms in PF5 : Axial – set of two
Equatorial – set of three
The axial F atoms have 3 nearest neighbors at 90.
The equatorial F atoms have 2 nearest neighbors at 90 & 2 nearest neighbors at 120.
The equatorial F atoms are less crowded than the axial F atoms!

60. Shape of SF6 Inspect central atom in Lewis diagram. Central S atom has
6 electron domains
6 atoms bonded to it
Shape is octahedral!
The S is allowed to have an “expanded octet” because it has empty 3d orbitals that can hold valence electrons.

61. Linear 2 points make a line!
Shape of all diatomics?

62. Trigonal Pyramid
Shape of NH3, NF3, PH3, etc?

63. Bent, with bond angle of 105
Shape of H2O, H2S, H2Se, etc.?

64. Tetrahedral
Shape of CH4, CCl4, etc.?

65. Polar Bond Bond has poles – the ends are different!
Bond has a permanent partial separation of charge
Polar Bond

66. Electronegativity Difference is 0.5 to 1.7
Polar Bond

67. No poles. Ends are the same. Symmetric electron cloud.
Nonpolar Bond

68. Nonpolar Bond Electronegativity difference = 0 to 0.5
NO separation of charge in bond.
Nonpolar Bond

69. Electronegativity difference  1.7
Ionic Bond

70. Full Separation of Charge At least +1 and -1.
Ionic Bond

71. Formula has a metal and a nonmetal
Ionic

72. Molecular Polarity
Depends on how the atoms are arranged in the molecule.
Some molecules which contain polar bonds are nonpolar overall. Common.
Some molecules which contain nonpolar bonds are polar. Less common.

73. The O end is a bit negative & the H end is a bit positive.
Polar.
Water is bent.
The O end is a bit negative & the H end is a bit positive.
WATER, H2O

74. Results from attractions between nucleus on 1 atom & electrons on another atom.
Bonding

75. releases energy.
Making a bond …

76. Absorbs energy.
Breaking a bond …

77. Covalent Compounds are
(almost all)
Molecular compounds.
Covalent Compounds are

78. Triple Bond N2

79. Double Bond O2

80. Single Bond
F2, Cl2, Br2, I2

81. When bonds are made, energy is …
released.
When bonds are made, energy is …

82. When bonds are broken, energy is …
absorbed.
When bonds are broken, energy is …

83. As the energy of a system , the stability generally …
increases.
As the energy of a system , the stability generally …

84. System releases energy. Its energy level goes down.
Exothermic

85. Properties of Molecular Substances
Soft
Low melting point & low boiling point
Does not conduct electricity in any phase
Does not dissolve in water
React slowly
Properties of Molecular Substances

86. Electrons are shared equally between the two atoms
Nonpolar Bonds

87. Molecule must contain polar bonds and they must be arranged asymmetrically.
Molecular Polarity

88. Molecular Polarity Depends on the shape (Bent & Pyramidal are polar
Linear & tetrahedral, polarity depends on composition.)
Molecular Polarity

89. Nonpolar Molecules Noble gas atoms (kickballs)
7 Diatomic Elements (footballs)
CXHY or pure hydrocarbons.
Larger molecules that have high symmetry
Nonpolar Molecules

90. If it’s not one of the 4 easy categories of nonpolar molecules, it is a polar molecule!

91. Nonpolar Molecules Weak Intermolecular Forces
(Dispersion or Van der Waals)
Low boiling points & melting points
Tend to be gases
Nonpolar Molecules

92. Polar Molecules Intermolecular Forces are Dipole-dipole forces
Stick together better than nonpolar molecules
Tend to have higher melting points, boiling points, Hf, & Hv than nonpolar substances.
Polar Molecules

93. Coordinate Covalent Bond
Covalent bond where both electrons in the bond are donated by 1 atom.
Coordinate Covalent Bond

94. Coordinate Covalent Bond
2 electrons to contribute. + H
H:N:H
H:N:H H .. ..
+ H+  .. ..
No electrons to contribute.
4 identical N-H bonds!
Coordinate Covalent Bond

95. Coordinate Covalent Bond
Both electrons in the bond are donated by the same atom.
Coordinate Covalent Bond

96. Compound that exhibits both covalent & ionic bonding
Compound that contains a polyatomic ion.
Compound that exhibits both covalent & ionic bonding

97. : : [Na]+1 [:O - H]-1 Lewis Diagram for NaOH Metal cation
: :
[Na]+1
Metal cation
Polyatomic anion
Lewis Diagram for NaOH

98. - :Cl:-1 : : Lewis Diagram for NH4Cl +1 H H – N – H Nonmetal anion
: :
Nonmetal anion
Polyatomic cation
Lewis Diagram for NH4Cl

99. - [:O - H]-1 : : Lewis Diagram for NH4OH +1 H H – N – H
: :
Polyatomic anion
Polyatomic cation
Lewis Diagram for NH4OH

100. How to calculate the polarity of a bond
Subtract the electronegativities of the 2 atoms.
How to calculate the polarity of a bond

101. To determine molecular polarity
Use the symmetry & conmposition of the molecule to help you.
Don’t get a number for it.
Just polar or nonpolar overall.
To determine molecular polarity

102. Low symmetry shapes: POLAR
Bent molecules
Pyramids, either trigonal or square base
See-Saw
T-shape
Low symmetry shapes: POLAR

103. High symmetry shapes Linear Trigonal PLANAR Tetrahedrons
Trigonal BIpyramids
Octahedrons
Square Planar
High symmetry shapes

104. For a high symmetry shape to be NONPOLAR
All the ends or corners have to match.
The corners or ends have to be the same element.
For a high symmetry shape to be NONPOLAR

105. Example of Symmetry & Composition
CX4 is nonpolar. Corners match!
CXY3 and CX2Y2 are polar.
Corners don’t match!
Example of Symmetry & Composition

106. Four network covalent substances are …
Cdia, Cgraph, SiO2, & SiC
Four network covalent substances are …

107. Network Covalent Substances form …
Crystal Lattices!
Network Covalent Substances form …

108. Properties of network covalent substances
High melting & boiling points
Hard
Brittle
Nonconductors
Properties of network covalent substances

109. Network Covalent substances have …
Strong directional covalent bonds
Network Covalent substances have …

110. Combinations of atomic orbitals on an atom
Combinations of atomic orbitals on an atom. Used to describe bonding in molecules.
Hybridization

111. Figuring out hybridization
One-to-one correspondence between number of domains and type of hybridization.
# of domains
Type of hybridization
Geometry of hybrid orbitals
# of p orbitals left over 2 sp
Linear 3
sp2
Trigonal planar 1 4
sp3
Tetrahedral 5
dsp3
Trigonal bipyramid 6
d2sp3
Octahedral
Figuring out hybridization

112. “Rules” for Hybridization
# of orbitals in = # of orbitals out.
Within a set of hybrid orbitals: orbitals have same energy & same shape but point in different directions.
Hybrid orbitals are different from the atomic orbitals used to construct them.
“Rules” for Hybridization

113. Result from combination of one s and three p atomic orbitals.
Produce 4 new orbitals pointing to the corners of a tetrahedron.
sp3 hybrid orbitals

114. Formed by “head-on” overlap of atomic orbitals.
Electron density is on the line connecting the two nuclei involved in the bond.
Sigma or  bonds

115. Result from side-to-side overlap of p orbitals.
Two regions of overlap, above and below the line connecting the two nuclei.
Pi or  bonds