1	Covalent Bonds and Molecular Structure Chapter 7
2	Bonds Ionic Bonds Electrostatic attractive forces Crystalline solids – no discrete molecules - formula units Identified by empirical formulas Metal + non-metal Covalent Bonds Shared electron bonds Discrete molecules, forms gases, liquids, and solids Identified by molecular formulas Non-metal + non-metal
3	Bond length - the optimum distance between nuclei in a covalent bond.
4	Bond dissociation energy – (Bond Strength) the amount of energy necessary to break a chemical bond in an isolated molecule in the gaseous state the amount of energy released when a bond forms Average bond dissociation energies are tabulated in the book.
5
6
7	Polar Covalent Bonds and Electronegativity
8	Bond Polarity
9	Electronegativity The ability of an atom in a bond to attract electrons toward itself. Electron greed Note that electronegativity increases up and to the right as do the ionization energy and the electron affinity
10
11	Lewis Electron Dot Structures Bonding electrons pairs – electron pairs involved in bonds Lone electron pairs – electron pairs that do not participate in bonding Bond order = number of bonds
12	Writing Lewis Dot Structures .Decide which atoms are bonded together - draw a skeleton structure .Count the total number of valence electrons available. .Find the number of electrons needed to give an octet around all atoms -- (remember H needs 2, all else need 8).
13	Writing Lewis Dot Structures Determine number of electrons short. .Number of bonds needed = number of electrons short/2. Distribute bonds -- (1st hook atoms together and then add double bonds where appropriate). Calculate number of electrons used in bonds.
14	Writing Lewis Dot Structures .Calculate electrons remaining. Distribute remaining electrons to give all atoms an octet. Done!!
15	Formal Charge The result of a method of electron bookkeeping that tells whether an atom in a molecule has gained or lost electrons compared to an isolated atom. Formal charge = # valence electrons – (# bonds + # electrons as lone pairs)
16	Expanded Octets Elements beyond neon have available d orbitals that may be used to accept additional electrons if necessary. If you the number of bonds necessary to hook all atoms together is greater than the number needed to give all an octet then put in necessary bonds and distribute extra electrons on atoms that have available d orbitals in which to expand.
17	Lewis Structures of ions for anions add the extra electrons to the number available for cations subtract the lost electrons from the number available
18	Resonance –In some Lewis structures, the multiple bonds can be written in several equivalent locations. All structures have the exact same energy. Which is the correct Lewis structure?? Answer : None alone are correct – the true molecule is a hybrid of the possible structures. The electrons are delocalized.
19	Definitions Sigma bond – the first bond to form between any two atoms forms between atoms Pi bond – second or third bond to form between two atoms forms above and below plane of the molecule
20	Predicting Shapes of Molecules To predict the shapes of molecules we look at the things (sigma bonds or lone pairs of electrons) surrounding them and put them as far from each other as possible. Valence Shell Electron Pair Repulsion (VSEPR) Theory
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45	"Molecular orbitals are to molecules..." Molecular orbitals are to molecules what atomic orbitals are to atoms. Molecular orbitals are formed by combining atomic orbitals. Bonding orbitals – decreased energy Antibonding orbitals – increased energy Electrons occupy molecular orbitals beginning with the MO of lowest energy. Bond order = antibonding electrons - MO bonding electons / 2.
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65