1. Intermolecular Forces
Intermolecular forces are the bonding forces that hold molecules together.
They are the main factor determining whether a substance is solid , liquid, or gas at room temperature.
Hydrogen bonds are the strongest IMF.
Polar bonds or dipole-dipole are the 2nd strongest.
All molecules have dispersion forces because of electron motions and these are the weakest IMF.

2. Isomers
Structural isomers are multiple structural models that represent a molecular formula.
Stereo-isomers are sturctural isomers that are mirror images of each other.