Chapter 9 Outline



9.1 Bonding Models and AIDS Drugs


9.2 Types of Chemical Bonds

This introduces ionic and covalent models for chemical bonds. In general ionic bonds are formed between metal and nonmetal atoms. Covalent bonds are formed between two nonmetal atoms. It is important to point out that bonds are not purely covalent or purely ionic, these are two models that describe bonding. Most chemical bonds are a mixture somewhere inbetween these two extreems.


9.3 Representing Valence Electrons with Dots

Valence Electrons. The valence electrons are the outtermost electrons around an atom. Since these are the electrons on the outside, they are the electrons that interact with neighboring atoms to make chemical bonds. This is where the action is for chemistry. We can generally ignore the inner electrons, because they don't do much chemistry. The Lewis dot structures are an important tool for keeping track of the valence electrons, learn how to use it, it will be an invaluable tool. If you take organic, you will use these constantly.

9.4 Ionic Bonding: Lewis Structures and Lattice Energies

Bonding in Ionic Compounds. Ionic bonds are formed between metal and nonmetal atoms. The further apart two atoms are on the periodic table, the greater the difference in their electronegativity, the more ionic the bond. The model for an ionic bond is the exchange of an electron. The more electronegative atom takes the electron, leaving one atom with a negative charge and the other with a positive charge. The bond then results from the attraction of opposite charges. Ionic compounds are generally found as extended crystal lattices, not as distinct molecules.

9.5 Covalent Bonding: Lewis Structures

Covalent bonds are formed between two nonmetal atoms. The closer together they are on the periodictable, the smaller the difference in their electronegativity, the more covalent the bond. The model for a covalent bond is sharing an electron. The bond results when two atoms share an electron so they have to be next to each other. Covalent compounds generally are distinct molecules. The octet rule and Lewis dot structures are tools to help determine the structure of compounds with covalent bonds. Pracice drawing Lewis dot structures, chemists use them very frequently. Drawing these structures is much like working a puzzle, there are rules for how many bonds each element will make, a correct structure does the best job of satisfying these rules. There are some exceptions and complications, but we will focus on what usually happens. Practice Lewis Structures - This is REALLY important.

9.6 Electronegativity and Bond Polarity

Electonegativity and dipole is a way to describe the shades of gray between an ideal covalent bond with electrons shared equally and an ideal ionic bond where electrons are traded.

9.7 Lewis Structures of Molecular Compounds and Polyatomic Ions


9.8 Resonance and Formal Charge

Resonance. This is a model that is used when there are multiple representations possible for the Lewis Structures.

Formal Charge. The covalent model for bonding is based on sharing electrons. Formal charge is a way to keep track of electrons to see if there is any charge on an atom in a structure. The assumption here is that non-bonding electrons belong exclusively to the atom they are located on and that bonding atoms are equally shared. This fromalism is a useful method to evaluate lewis dot structures and to discuss the behavior of molecules. However, when one of the atoms is more electronegative this sharing is not equal. The more electronegative element gets more of the electron density. Bond polarity and electronegativity are a way to decide how the electron is shared. You should be able to determine the formal charge for each atom in a structure, determine the direction and magnitude of the dipole.


9.9 Exceptions to the Octet Rule: Odd-Electron Species, Incomplete Octets, and Expanded Octets

Atoms for many elements do not always follow the octet rule. Use the periodic table and the electron configurations for the atoms to make sense of this section.

9.10 Bond Energies and Bond Lengths

This section disussses bond order (single, double and triple bonds), bond length (look it up in the table), and bond energy (look it up in the table). Bond energy is an important concept because it can be used to solve for /\H. When /\Hf values are not available for all the products and reactants, you can look at a chemical reaction as a series of breaking and making bonds. The bond energy is the energy required to break a bond (or the energy released when a bond is produced). Simply add up the energy required to break bonds and subtract the energy released when bonds are made to find /\H for a reaction. Be certain to keep track of which bonds are broken, which are made, and how many of each.

9.11 Bonding in Metals: The Electron Sea Model


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