Aim: How do chemists write “half- reactions”? Each atom has a nucleus, with an overall positive charge, surrounded by negatively charged electrons. Each electron in an atom has its own distinct amount of energy. An oxidation-reduction (redox) reaction involves the transfer of electrons (e-).

Aim: How do chemists write “half- reactions”? Reduction is the gain of electrons. A half-reaction can be written to represent reduction. Oxidation is the loss of electrons. A half-reaction can be written to represent oxidation. Oxidation numbers (states) can be assigned to atoms and ions. Changes in oxidation numbers indicate that oxidation and reduction have occurred.

Aim: How do chemists write “half- reactions”? In all chemical reactions there is a conservation of mass, energy, and charge. In a redox reaction the number of electrons lost is equal to the number of electrons gained.

Aim: How do chemists write “half- reactions”? Essential Questions: Why is it only electrons that are transferred in chemical reactions? How does one assign oxidation numbers? How do chemists determine which elements are oxidized and which ones are reduced in in “redox” reaction? Why does reduction and oxidation always occur simultaneously?