Cell Representation (Cell Notation)

Describing a galvanic cell fully — the electrode materials, which one is oxidized and which is reduced, and the concentrations involved — normally takes several sentences or a diagram. Cell notation (or cell representation) condenses all of that into a single standardized line.

The convention, read strictly left to right, is: the anode's solid electrode material, a single vertical line (representing the phase boundary between the solid electrode and its solution), the anode's solution with its concentration in parentheses, a double vertical line (representing the salt bridge), the cathode's solution with its concentration, a single vertical line, and finally the cathode's solid electrode material. For the Daniell cell this gives: $\text{Zn}(s)\ |\ \text{Zn}^{2+}(1\ \text{M})\ ||\ \text{Cu}^{2+}(1\ \text{M})\ |\ \text{Cu}(s)$.

Reading this notation, a chemist immediately knows: the species written first (leftmost) is oxidized (so zinc is the anode here), and the species written last (rightmost) is reduced (so copper is the cathode) — this ordering is fixed and never reversed, regardless of which electrode happens to be drawn on the left in a diagram of the physical setup. If either half-cell involves an inert electrode (such as platinum or graphite, used when neither half-reaction involves a solid metal — for example a hydrogen-gas or a redox half-cell like $\text{Fe}^{2+}/\text{Fe}^{3+}$), the inert electrode material is still written at the corresponding end, with the actual reacting species and any gas pressure noted alongside it, separated by a comma. …