AP CHAPTER 8 OUTLINE
CHEMICAL BONDING:
GENERAL CONCEPTS
I. Electron Transfer and the Formation of Ionic Compounds
A. Conditions that favor the formation of ionic compounds
1. Ionic bonding -- attraction between positive and negative ions in an ionic compound (electron transfer)
a. There must be a net lowering of PE for a stable compound to form from its elements
B. Importance of the Lattice Energy
1. Lattice energy -- amount that the PE decreases in a system when the ions are brought from a gaseous state to the position the ions occupy in a crystal of the compound
a. The lattice energy must be greater than the combined ionization energy and vapaorization energy for an ionic compound to form
C. Why Metals Form Cations and Nonmetals Form Anions
1. Metals - small ionization energy and electron affinity
a. Little energy is needed to remove an electron
2. Nonmetals - large inization energy and electron affinity
a. Lots of energy needed to remove an electron
3. Changes in Electron Configurations when Ions Form: The Octet Rule
a. When representative elements form ions, they tend to gain or loss enough electrons to have a noble gas configuration (most stable - filled valence shell)
b. Octet Rule -- atoms tend to gain or lose electrons until they achieve an outer shell with 8 (octet) electrons
c. Ex. -- Sodium will lose one electron to make Na+ ion, it will not lose a second electron since the ionization energy is greater than the lattice energy
4. Exceptions to the Octet Rule
a. The first electrons to be lost by an atom or ion are always those from the shell with the largest n value
b. As electrons are removed from a given shell, they come from the highestenergy occupied subshell (s<p<d<f)
II. Electron Bookkeeping: Lewis Symbols
A. Lewis symbol -- the chemical symbol surrounded by dots to represent valence electrons
1. Valence electrons = group # for representative elements
III. Electron Sharing: The Formation of Covalent Bonds
A. Energy Changes in the Formation of a Covalent Bond
1. Molecules -- electrically neutral substances (2 nonmetals)
a. All ionization energies are high, will not form ionic compounds, electrons share
2. Covalent bond -- net attractive force by the sharing of two electrons
a. Bond length (bond distance) -- average distance etween tow atoms bonded together
b. Bond energy -- amount of energy released or absorbed when a bond is formed or broke
B. Pairing of Electrons
1. Electron pair bond -- another name for a covalent bond
2. Lewis formula (Lewis structure) -- Lewis symbols with dashes to represent bonds
a. Structural formula -- shows both the atoms involved in molecule and how they are bonded together
C. Covalent Bonding and the Octet Rule
1. Octet rule - When atoms form covalent bonds, they tend to share sufficient electrons to achieve an outer shell having eight (octet) electrons
a. Covalent bonds fill the s and p subshells
b. Use octet rule to explain the number of covalent bonds in a molecule
D. Multiple Bonds
1. Single bond -- sharing of one electron pair
2. Double bond -- sharing of two electron pairs
3. Triple bond -- sharing of three electron pairs
IV. Some Important Compounds of Carbon
A. Organic compounds -- compounds containing carbon, hydrogen, oxygen, and nitrogen
1. Isomers -- same formula, but different structure
B. Compounds That Also Contain Oxygen and Nitrogen
1. Alcohol
a. R - OH
2. Ketone
a. R - C - R
O (double bonded to C)
3. Aldehyde
a. R - C - H
O (double bonded to C)
b. Carbonyl group --> C = O
4. Carboxylic acid
a. R - C - OH
O (double bonded to C)
b. Carboxyl group
5. Amines
a. R - NH2
V. Electonegativity and Polarity of bonds
A. electronegativity -- the relative attraction of an atom for an electron
1. When two atoms have the same electronegativity, they share the electrons equally
2. when two atoms have different electronegativity, they share the electrons unequally
a. Partial charge -- slight charges on each atom due to unequal sharing of electrons
3. Polar (covalent) bonds -- bonds that carry partial charges
a. Dipole -- two poles of the bond
4. Polar molecule -- a molecule with polar bonds, therefore, the molecule is polar
a. Dipole moment -- multiplying the amount of charge on either end by the distance between the charges
5. Nonpolar (covalent) bond -- bonds in which the electrons are equally shared
a. Nonpolar and Ionic bonds are the extremes of bonding
1. Ionic character -- the degree to which the bond is polar (ionic)
B. Trends in Electronegativity in the Periodic Table
1. EN decreases as you go down the table
2. EN increases as you go across the table
VI. Electronegativity and the Reactivities of Metals and Nonmetals
A. Reactivities of Metals
1. Metals oxidize to form positive ions (oxidation states)
a. As electronegativity increases, the metal becomes less easily oxidized
b. Metals that are most easily oxidized on are on the far left of the table
B. Oxidizing Power of Nonmetals
1. Nonmetals act as oxidizing agents
a. As electronegativity increases, the nonmetals become stronger oxidizing agents
b. Nonmetals that are the strongest oxidizing agents are on the top right of the table
VII. Drawing Lewis Structures
A. A Method for Drawing Lewis Structures
1. Decide which atoms are bonded (skeletal structure)
2. Count all valence electrons
3. Place two electrons in each bond
4. Complete the octets of the atoms attached to the central atom by adding electrons in pairs
5. Place remaining electrons on the central atom in pairs
6. If the central atom does not have an octet, form double bonds, if necessary, for triple bonds
B. The octet rule is not always followed
1. With the exception of period 2, most nonmetals can have more than the octet of electrons
a. Reason -- n = 2 can only hold 8 electrons maximum
b. They can have less than the octet, however
2. If you must guess on the skeletal structure, guess the most symmetrical
a. Usually, the lowest electronegativity atom goes in the center
IX. Resonance: When a Single Lewis Structure Fails
A. Resonance -- when we view the actual structure of a molecule or ion as an average of all the resonance structures
1. Resonance structure (contributing structure) -- Possible structure of the molecule or ion
2. Resonance hybrid -- the actual structure of the molecule or ion
3. If you must move electrons to create one or more double bonds, then the number of resonance structures equal the number of equivalent choices for the locations of the double bond
B. Effect of Resonance on the Stability of Molecules and IOns
1. Resonance hybrid has less total energy then the resonance structures
a. More stable than resonance structures
b. Resonance energy -- the difference of energy between the resonance hybrid and the resonance structures
X. Coordinate Covalent Bond -- a bond in which one atom contributes a complete electron pair for both atoms to share
Outline based upon:
Brady, J. E., Holum, J. R., Russell, J. W. (2000). Chemistry: The Study of Matter and Its Changes. (3rd ed.). New York: John Wiley & Sons, Inc. pp. 325-358.
