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12 chem unit 2 Cheat Sheet by

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Resonance Structures

Equivalent resonance structures contain the same number of single or multiple bonds and each atom ahs the same formal charge
The best resonance structure has the following criteria:
Non-eq­­ui­v­alent resonance structures have different numbers of bonds and different formal charge distri­­bution
1. Smaller formal charges (+ or -) are preferred over larger ones
Formal charge = # of valence electrons - (# bonded electrons + lone pairs)
2. Like formal charges on adjacent atoms are not desirable
Overall charge = sum of formal charges
3. Negative formal charges should reside on a more electr­one­gative atom

Interm­ole­cular Forces

Intram­ole­cular forces occur within molecules and are strong forces
London dispersion forces occur in all molecules and get stronger as the length of the molecule increases
 

Hybrid­ization

Atomic orbitals overlap to form a new orbital with a pair of opposite spin electrons. This is valence bond theory
Sigma bonds are the first single bonds between 2 atoms
Hybrid orbitals can be determined by the VSEPR structure of a molecule, or by looking at the total # of electron groups
Pi bonds are the second or third bonds between 2 atoms
Partially filled orbitals in the hybridized orbitals represent single bonds
Unhybr­idized p orbitals represent Pi bonds
Filled orbitals represent lone pairs
To create equal orbitals, you may have to promote an ns electron to a np electron
Partially filled s and p orbitals can overlap to share electrons
 

Interm­ole­cular Forces

Intram­ole­cular forces occur within molecules and are strong forces
London dispersion forces occur in all molecules and get stronger as the length of the molecule increases
Interm­ole­cular forces occur between molecules and are weaker forces
London dispersion forces are caused when an instan­taneous dipole attracts another instan­taneous dipole
The strength of an interm­ole­cular force is dependent on the size of the molecule, the surface area of the molecule, and the polarity of the molecule
Created by the constant movement of molecules
Dipole­-dipole forces exist in all polar molecules
London dispersion forces are the weakest IMF
A permanent dipole exists in polar molecules due to the difference in electr­one­gat­ivity of bonded atoms
Hydrogen bonding occurs when hydrogen bonds with N, F, or O
The positive end of one molecule will attract the negative end of another and vice versa
Hydrogen bonds are very strong IMF
Ion-dipole forces occur between ions and polar molcules
Stronger IMFs lead to higher boiling points and lower melting points
 

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