166 ❯ STEP 4. Review the Knowledge You Need to Score High
● The number of hybrid orbitals is the same as the number of atomic orbitals that were
mixed together.
● There are a number of different types of hybrid orbital, such as sp, sp^2 , and sp^3.
● In the valence bond theory, sigma bonds overlap on a line drawn between the two nuclei,
while pi bonds result from the overlap of atomic orbitals above and below a line connect-
ing the two atomic nuclei.
● A double or triple bond is always composed of one sigma bond and the rest
pi bonds.
● In the molecular orbital (MO) theory of covalent bonding, atomic orbitals form molecu-
lar orbitals that encompass the entire molecule.
● The MO theory uses bonding and antibonding molecular orbitals.
● The bond order is (# electrons in bonding MOs – # electrons in anti-bonding MOs)/2.
● Resonance occurs when more than one Lewis structure can be written for a molecule.
The actual structure of the molecule is an average of the Lewis resonance structures.
● The higher the bond order, the shorter and stronger the bond.
● Paramagnetism, the attraction of a molecule to a magnetic field, is due to the presence
of unpaired electrons. Diamagnetism, the repulsion of a molecule from a magnetic field,
is due to the presence of paired electrons.