1. Unit 8 – Bonding and Molecular Geometry
Honors Chemistry

2. Ionic Bond

3. Ionic Bonds Bond energy – energy required to break a bond
Atoms bond to achieve the lowest possible energy
Very strong mutual attraction
Ionic bonding
Occurs between a metal + nonmetal
Metals give up electrons and nonmetals gain them

4. Binary Ionic Compounds
Solid crystals
Ions align themselves:
To maximize attractions between opposite charges
To minimize repulsion between like ions.
React to achieve noble gas configuration

5. Partial Ionic Character
There are probably no totally ionic bonds between individual atoms
More than 50% ionic character is considered ionic
Problem with substances containing polyatomic ions
New definition: ionic compound is any compound that conducts an electric current when melted

6. Covalent Bonds
The electrons in each atom are attracted to the nucleus of the other.
But the electrons repel each other, and the nuclei repel each other.
To reach a distance with the lowest possible energy.
The distance between is the bond length.
Electrons are shared between atoms

7. Differences between ionic and covalent bonds.
Some Physical Properties of NaCl and Cl2
NaCl
Cl2
Phase at room temperature
Solid
Gas
Density
2.165 g/cm3
g/cm3
Melting point
801°C °C
Boiling point
1413°C
-34.6°C
Ability of aqueous solution to conduct electricity
Conducts
Does not conduct

8. Covalent Bonding Two extremes: 1. Polar covalent bond.
The electrons are not shared evenly.
One end is slightly positive, the other negative
Difference in electronegativity is indicated d
Difference in electronegativity between atoms tells us how polar

9. H - F H - F H - F H - F H - F H - F H - F H - F d+ d- d+ d- d+ d- d+

10. - + H - F H - F H - F H - F H - F H - F H - F H - F d+ d- d+ d- d+ d-

11. - + H - F H - F H - F H - F H - F H - F H - F H - F d+ d- d+ d- d+ d-

12. Electronegativity
difference
Bond
Type
Non-polar
Covalent
Zero
Covalent Character
decreases
Ionic Character increases
Polar
Covalent
Intermediate
Ionic
Large

13. Example Order the following bonds according to polarity:
H—H
Cl—H
S—H
F—H
H—H < S—H < Cl—H < F—H
0 < 0.4 < 0.9 < 1.9
Polarity of the bond increases as the difference in electronegativity increases

14. Covalent Bond Energies
Single bond – share one pair
Double bond – share two pairs
Triple bond – share three pairs
The more pairs shared, the shorter the bond length

15. Metallic Bonds
The electrons from metals form a “sea” of electrons that flow around the metal ions
Called delocalized - they are not fixed in one place
The metal cations and the electrons are oppositely charged and are attracted to each other

16. Types of Bonds: Metallic
As result of the delocalized electrons metals are:
Malleable
Ductile
High melting and boiling points
Conduct heat and
electricity

17. Unit 8 – Molecular Geometry
PART 2

18. Lewis Structure Shows how the valence electrons are arranged.
One dot for each valence electron.
A stable compound has all its atoms with a noble gas configuration.
Hydrogen follows the duet rule.
The rest follow the octet rule.

19. Rules For Lewis Structures
Sum the valence electrons.
Use a pair to form a bond between each pair of atoms.
Arrange the rest to fulfill the octet rule (except for H and the duet). A line can be used instead of a pair.
Example:
H2O
NH3
CH4

20. Exceptions to the Octet Rule
BH3
Be and B often do not achieve octet
Have less than an octet, for electron deficient molecules.
SF6
Third row and larger elements can exceed the octet
Use 3d orbitals

21. Resonance
Sometime more than one valid Lewis structure is possible for a molecule
Resonance structures show an average
Use double arrows to indicate it is the “average” of the structures
Example:
NO3-

22. VSEPR THEORY VALENCE SHELL ELECTRON PAIR REPULSION
Predicts the shape of molecules and ions in which valence shell electron pairs are arranged about each atom so that they are kept as far away as possible, thus minimizing electron-pair repulsion

23. HOW DO WE DETERMINE SHAPE?
Draw Lewis dot diagrams
Determine how many bonding pairs
Determine how many lone pairs
Use VSEPR to arrange atoms
Draw structure
Lone pairs take more space
Multiple bonds count as one pair (double or triple bonds)
Remember: the more pairs shared, the shorter the bond length
Let’s try CCl4

24. Summary of Molecular Shapes
Type of Molecule
Molecular Shape
Atoms Bonded to Central Atom
Lone Pairs of Electrons
on central atom
Formula Example
Linear 2
CO2
Bent 1
SnF2

25. Summary of Molecular Shapes
Type of Molecule
Molecular Shape
Atoms Bonded to Central Atom
Lone Pairs of Electrons on central atom
Formula Example
Trigonal Planar 3
BH3
Tetrahedral 4
SiH4

26. Summary of Molecular Shapes
Type of Molecule
Molecular Shape
Atoms Bonded to Central Atom
Lone Pairs of Electrons on central atom
Formula Example
Trigonal Pyramidal 3 1
PCl3
Bent 2
SCl2

27. Summary of Molecular Shapes
Type of Molecule
Molecular Shape
Atoms Bonded to Central Atom
Lone Pairs of Electrons on central atom
Formula Example
Trigonal bipyramidal 5
PF5
Octahedral 6
SeCl6

28. VSEPR

29. Bond Angles Shape Bond Angles Linear 180° Trigonal Planar 120°
Tetrahedral
109.5°
Trigonal Pyramidal
90° °
Bent
Trigonal Bipyramidal
90° & 120°
Octahedral
90°

30. WHAT IS POLARITY?
Polarity depends on the type of bond and shape of molecule.
Any molecule that has a net separation of charge (dipole moment)
Ionic bonds: Polar
Covalent Bonds:
Nonpolar-nonpolar
Polar-depends on shape

31. How Do We Determine Polarity?
Determine bond type
Determine Shape
Draw arrows showing direction of poles
If arrows cancel each other out: NONPOLAR
If arrows go toward one direction: POLAR

32. Polarity and Geometry Three shapes will cancel them out.
***** ALL BONDS MUST BE THE SAME****
Linear

33. Polarity and Geometry 120º Three shapes will cancel them out.
Planar triangles
120º

34. Polarity and Geometry
Three shapes will cancel them out.
Tetrahedral

35. Polarity and Geometry
Others don’t cancel
Bent

36. Polarity and Geometry
Others don’t cancel
Trigonal Pyramidal

37. Why Do we do this? Like dissolves like!
Polar molecules will dissolve in polar molecules but not in non-polar molecules