Based on thermodynamic arguments, a simple formula is derived that relates the 2D-isothermal compressibility, k(2D), directly to (partial derivative L-D/partial derivative E)(T) and (partial derivative L-D/partial derivative N)(T), where LD is the stripe separation of the Au(1 1 1) surface, E is the applied electrode potential and N is the surface concentration of deposit. It accounts for the deposition-induced compression of the top most Au(1 1 1) surface layer during gold deposition. Furthermore, the value of k(2D) for the deposited gold layer on Au(1 1 1) surface has been experimentally determined. The results reveal that the k(2D)value for gold does not match the reported trend for other metals. (C) 2009 Elsevier B.V. All rights reserved.