[CHEM 2OA3] Comprehensive Midterm Exam guide including any lecture notes, textbook notes and exam guides.find more resources at oneclass.com
CHEM, chapter one
We can construct all compounds by combining atomic molecules, forming degenerate
All the bonds in this molecule has an antibonding MO
Sigma bonds: low in energy, head-on overlap
Sigma star: high in energy, complimentary
Pi star: high in energy
Strongest to weakest: Sigma, Pi, Pi star, Sigma star
Pi is weaker than sigma â if we start with an alkene, we destroy the pi bond during a
reaction, but the sigma bond remains intact.
Bond length: sigma bond between sp: s e closer to the nucleus.
More s character: sp bond is shorter than an sp3 bond.
Bond length contracts as hybridization becomes more s in character
Bond strength increases as the hybridization becomes more s in character
Double bond is stronger than single bond
Valence shell electron pair repulsion (VSEPR)
1. Determine the steric number (number of substituents around the atom)
Methane steric number: 4.
Lone pairs count as steric numbers â it behaves as a substituent when finding
When steric number is four, we need four orbitals (hybridize one s and 3 p in
methane). When steric number is three, sp^2. When steric number is two, sp.
For any sp^3 hybridized atom, the 4 valence e pairs will form a tetrahedral e group geo
Lone pairs repel bonded pairs more than bonded pairs repel bonded pairs.
Number of lone pairs impacts the bond angles.
The geometry of ammonia: trigonal pyramidal.
BF3: six e species, strong lewis acid. Steric number of 3 â hybridization is sp2. Unlike
ammonia, because there is no lone pair, there is a trigonal molecular geometry.
Boroâ¯ has aâ¯ uâ¯hyâ¯ridized p orâ¯ital, â¯ut it is eâ¯pty, so it doesâ¯ât â¯ouâ¯t. Itâs just a regioâ¯
of space where e could be if they wanted to. If we were to react BF3 with an e donor,
the p orbital tells us where the e could go if we were to add them.
Lone pair, sigma bond to C on left, sigma to C on right, pi bond
Sp^2 hybridized â one of the two sp^2 hybrids will accommodate the lone pair, the
others will hang with C
find more resources at oneclass.com