7 The Electrified Interface.- 7.1 Electrification of an Interface.- 7.1.1 The Electrode-Electrolyte Interface: The Basis of Electrodics.- 7.1.2 New Forces at the Boundary of an Electrolyte.- 7.1.3 The Interphase Region Has New Properties and New Structures.- 7.1.4 An Electrode Is Like a Giant Central Ion.- 7.1.5 The Consequences of Compromise Arrangements: The Electrolyte Side of the Boundary Acquires a Charge.- 7.1.6 Both Sides of the Interface Become Electrified: The So-Called Electrical Double Layer.- 7.1.7 Double Layers Are Characteristic of All Phase Boundaries.- 7.1.8 A Look into an Electrified Interface.- Further Reading.- 7.2 Some Problems in Understanding an Electrified Interface.- 7.2.1 What Knowledge Is Required before an Electrified Interface Can Be Regarded as Understood?.- 7.2.2 Predicting the Interphase Properties from the Bulk Properties of the Phases.- 7.2.3 Why Bother about Electrified Interfaces?.- 7.2.4 The Need to Clarify Some Concepts.- 7.2.5 The Potential Difference across Electrified Interfaces.- 7.2.5a What Happens when One Tries to Measure the Absolute Potential Difference across a Single Electrode-Electrolyte Interface.- 7.2.5b The Absolute Potential Difference across a Single Electrified Interface Cannot Be Measured.- 7.2.5c Can One Measure Changes in the Metal-Solution Potential Difference?.- 7.2.5d The Extreme Cases of Ideally Nonpolarizable and Polarizable Interfaces.- 7.2.5e The Development of a Scale of Relative Potential Differences.- 7.2.5f Can One Meaningfully Analyze an Electrode-Electrolyte Potential Difference?.- 7.2.5g A Thought Experiment Involving a Charged Electrode in Vacuum.- 7.2.5h The Test Charge Must Avoid Image Interactions with the Charged Electrode.- 7.2.5i The Outer Potential ? of a Material Phase in Vacuum.- 7.2.5j What is the Relevance of the Outer Potential to Double-Layer Studies?.- 7.2.5k Another Thought Experiment Involving an Uncharged, Dipole- Covered Phase.- 7.2.5l The Dipole Potential Difference M?S? aclÃF