One group replaces another. 

Characteristic reactions of saturated compounds such as alkanes and alkyl Halides and of aromatic compunds. 

All parts of the adding reagent appear in the product; two molecules become one.

Characteristic of compounds with multiple bonds. 

One element loses the elements of another small molecule. 

ex: dehydrohalogenation 

Used to prepare compunds with double and triple bonds.

When a bond breaks such that one fragment takes away both electrons of the bond, leaving the other fragment with an empty orbital. 

Produces charged fragments 

ionic reaction