1. CHEMICAL BONDING Set 1 Cocaine
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2. Credits
Thank you to Mr. Neil Rapp who provided the bulk of this powerpoint on his website

3. Chemical Bonding Problems and questions —
How is a molecule or polyatomic ion held together?
Why are atoms distributed at strange angles?
Why are molecules not flat?
Can we predict the structure?
How is structure related to chemical and physical properties?

4. Review of Chemical Bonds
There are 3 forms of bonding:
ionic—complete transfer of 1 or more electrons from one atom to another (one loses, the other gains) forming oppositely charged ions that attract one another
covalent—some valence electrons shared between atoms
metallic – holds atoms of a metal together
Most bonds are somewhere in between ionic and covalent.

5. Why do atoms bond in these ways?
A bond will form if the energy of the resulting molecule is lower than that of the separated atoms.
Bond energy: the energy required to break a bond
Bond length: the distance where the energy is minimal
Zumdahl, Steven, and Susan Zumdahl. Chemistry. Boston: Houghton Mifflin, 2003.

6. The type of bond can usually be calculated by finding the difference in electronegativity of the two atoms that are going together.

7. Electronegativity Difference
If the difference in electronegativities is between:
1.7 to 4.0: Ionic
0.45 to 1.7: Polar Covalent (uneven sharing of electrons)
0.0 to 0.45: Non-Polar Covalent (even sharing of electrons)
Example: NaCl
Na = 0.8, Cl = 3.0
Difference is 2.2, so
this is an ionic bond!

8. Learning Check: Relative Bond Polarities
Order the following bonds according to increasing polarity: H-H, O-H, Cl-H, S-H, and F-H.

9. Ionic Bonds
All those ionic compounds were made from ionic bonds. We’ve been through this in great detail already. Positive cations and the negative anions are attracted to one another (remember the Paula Abdul Principle of Chemistry: Opposites Attract!)
Therefore, ionic compounds are usually between metals and nonmetals (opposite ends of the periodic table).

10. Ions: Electron Configurations and Sizes
Atoms in stable compounds usually have a noble gas electron configuration
When two nonmetals react to form a covalent bond, they share electrons in a way that completes the valence electron configurations of both atoms. That is, both nonmetals attain noble gas electron configurations.
When a nonmetal and a metal react to form a binary ionic compound, the ions form so that the valence electron configuration of the nonmetal achieves the electron configuration of the next noble gas atom and the valence orbital of the metal are emptied. In this way, both ions achieve noble gas electron configurations.
Zumdahl, Steven, and Susan Zumdahl. Chemistry. Boston: Houghton Mifflin, 2003.

11. Predicting Formulas of Ionic Compounds
It should be emphasized that when chemists use the term ionic compound, they are usually referring to the solid state of the compound
In the solid state of an ionic compound, the ions are relatively close together and many ions are simultaneously interacting
In the gas phase of an ionic substance the ions would be relatively far apart and would not contain large groups of ions
Solid ionic compounds contain a large collection of positive and negative ions packed together in a way that minimizes the (-)(-) and (+)(+) repulsions and maximizes the (+)(-) attractions.
Zumdahl, Steven, and Susan Zumdahl. Chemistry. Boston: Houghton Mifflin, 2003.

12. Homework Questions
1) Explain the difference between the following pairs of terms.
A. electronegativity and electron affinity
B. covalent bond and polar covalent bond
C. polar covalent bond and ionic bond
2) Some of the important properties of ionic compounds are as follows:
Low electrical conductivity as solids and high conductivity in solution or when molten
Relatively high melting and boiling points
Brittleness
Solubility in polar solvents (e.g., water)
How does the concept of ionic bonding discussed in previous units account for these properties?

13. Homework Questions Cont’d
3) Predict which bond in each of the following groups will be the most polar.
A. C-F, Si-F, Ge-F
B. P-Cl, or S-Cl
C. S-F, S-Cl, S-Br
D. Ti-Cl, Si-Cl, Ge-Cl