Atoms are the basic building blocks of all molecules. In organic molecules, they are held together with covalent bonds.
Important properties:
Electronegativity (EN)
How strongly an atom pulls electrons toward itself. F has the greatest EN.
Polarizability
How much of a temporary dipole can be created by shifting the electron cloud around an atom. Roughly, how “sloshy” the electron cloud is. For example, S is more polarizable than O.