Reasons for the formation of free electrons
Metal atoms generally have fewer electrons in the outer layer, and the nucleus is less attractive to them. When metal atoms combine to form a metal crystal, the outer layer electrons leave the parent atom and become free electrons. Many, many free electrons form an electron cloud (or electron gas). Under the action of an external electric field, free electrons can undergo directional movement to form a current.
Electrons are attracted by the nucleus and move around the nucleus. The attraction of atomic nuclei is divided into strong and weak. When two different atoms are close to each other, under certain conditions (such as temperature rise), the speed of electrons outside the nucleus is accelerated, making the electrons more attractive. The nucleus attracts the past and leaves the original nucleus to form a free electron. Another reason is that due to external conditions (such as temperature rise), the electron's ability to move is improved. Since the attraction ability of atomic nuclei is realized within a certain range, the temperature increases the kinetic energy of the electron and increases its ability to move. With a certain probability, the movement beyond the attraction range of the atomic nucleus will cause the electrons to escape from the bondage of the atomic nucleus and form a free electron. The former reason belongs to chemical change, the latter should belong to physical change, because no new substance is formed, but the process of forming the latter free electron is exactly an intermediate reaction link of a complete chemical reaction.