A large portion of materials around us are polar. The constituents of these materials, molecules or atoms, have positive or negative charge. Atoms in a salt structure have both positive or negative charges and the electrostatic force between opposite charges, ionic force, sticks atoms together in the solid state. A charged species is called ion. When salt is passed into the water, water molecules crawl into the salt structure and break it apart into its ions. Now these ions can move freely in the liquid and since they have charge, we can manipulate them by applying an electric field. This is one of the main cases in which electricity plays a role in chemistry. This area of science is called electrochemistry. Usually an electrochemical system is made up of an ionic solution, electrolyte, and two conductive parts as positive and negative electrodes, anode and cathode. Positive metal ions in the solution are drawn by the negative electrode, cathode. Cathode is a storage of a large number of electrons. When positive ions get to the cathode, they can easily grab some electrons from the cathode surface and neutralize. The neutralized species are metal atoms, and they are not soluble in water so they stick to the cathode surface. After a while, they make a negative replica of the cathode shape. By using different cathode shapes we can make different metallic structures. These structures are built atom by atom so they can conform exactly to the cathode shape. Due to this reason, electrochemical techniques are used for making metallic structures in micro and nano scales.
An electrochemical process consists of two main parts. The first part is the mass transfer process which causes moving of the positive ions in the solution toward the negative electrode. The second part is an electrochemical reaction which occurs on the cathode surface and converts metal ions to the neutralized atoms. In this reaction electrons are transferred from the cathode surface to the adjacent ions in the solution. Electrons, like people, have different moving rates in different conditions. The rate of the electron transfer depends on different process conditions like the cathode material, electrolyte composition, surface structure of the cathode et. al and we can measure this rate using electrochemical methods.