Adsorption site

An adsorption site is a position or local environment at which a chemical species can be retained at a boundary. Treating all adsorption sites as identical is an assumption about their binding properties, not a definition of adsorption.

In a one-molecule-per-adsorption site description, surface coverage is $\theta =N_{\mathrm{occupied}}/N_{\mathrm{sites}}$, with $0\le \theta \le 1$. For a macroscopic sample at chemical equilibrium, $\theta$ usually denotes the mean occupied fraction. Inferring it from total uptake also requires the capacity of a complete monolayer.