A quick note on hybridization: it is essentially the mixing of atomic orbitals to rationalize observed chemical and structural trends. Simply, if add an S orbital to a P orbital we get a SP hybrid. To determine the hybridization for an atom in a molecule, add the number of attached atoms to the number of non-bonding electron pairs (non-delocalized). Then use the table in the picture.
Sigma Bonds: consists of two electrons that are localized between two nuclei. It is a very strong bond bond is always the first type of bond to be formed between any two atoms; a single bond must be a sigma bond.
Pi bonds: composed of two electrons that are localized to the region that lies on opposite sides of the plane formed by the two bonded nuclei and immediately adjacent atoms (not directly between like sigma bonds). Is formed by the side-to-side aligment of two unhybridized p orbitals. The electrons in a pi bond are further from the nuclei than the electrons of a sigma bond, and therefore at a higher energy level, less stable, and form a weaker bond. Note that pi bonds prevent rotation.
**In any multiple bond, there is only one sigma bond and the remainder are pi bonds.
Saturation: a molecule is said to be saturated if it contains no pi bonds and no rings; therefore, it is unsaturated if it has at least one pi bond or a ring.
To determine the degree of unsaturation use this formula: {(2n+2)-x}/2
n=number of carbons
x=number of hydrogens (plus any monovalent atoms such as halogens like F, Cl, Br, or I.
One degree of unsaturation indicates the presence of one pi bond or one ring, two degrees indicates two pi bonds (2 separate double bonds or one triple bond), or one pi bond and one ring, two rings, etc.
**Each oxygen (or other divalent atom) "replaces" one carbon and 2 hydrogen atoms
**Each nitrogen (or other trivalent atom) "replaces" one carbon and 1 hydrogen atom
Let's touch on bond dissociation energy (BDE). By definition, it is the energy required to break a bond homolytically. In homolytic bond cleavage, one electron of the bond being broken goes to each fragment of the molecule. Two radicals form in the process. This is different from heterolytic bond cleavage where both electrons of the electron pair that make up the bond go to the same atom; this forms a cation and an anion
**The higher the bond order, the shorter and strong the bond.
**When comparing the same types of bonds, the greater the S character in the component orbital, the shorter the bond (because s-orbitals are closer to the nucleus than p-orbitals).
**The longer the bond, the weaker it is
ERROR: on my picture it should say "degree of unsaturation", not "saturation" at the bottom. Sorry
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