Free electrons are not confined to aatomInternalElectronics。Such electrons can move in matter or vacuum under the action of an external electric or magnetic field.For example, the combination of atoms into metal crystals mainly depends on the valence electrons in the outer layer of atoms and some of the inner electrons.Under normal circumstances, some valence electrons can leave the atom and move freely in the crystal lattice.Such electrons are called free electrons.[1]
Not only the free charge in the metal conductor,semiconductorFree charge in andinsulatorThe trace free charge in belongs to free electrons.The number of free electrons will affect the conductivity and thermal conductivity of materials. The more free electrons, the stronger the conductivity.MostMetalThere are a considerable number of free electrons,NonmetalThe opposite is true.(There are exceptions, such asgraphite。）
Causes
Announce
edit
The number of outer electrons of metal atoms is generally small, and the attraction of atomic nuclei is weak.When metal atoms combine to form metal crystals, the outer electrons break away from the parent atoms and become free electrons.Many free electrons form an electron cloud (or electron gas).Under the action of external electric field, free electrons can move directionally to form current.[2]
Electrons are subject toNucleusMoving around the nucleus of an atom because of its attraction.The attraction of atomic nucleus can be strong or weak. When two different atoms are close, the movement speed of electrons outside the nucleus is accelerated under certain conditions (such as temperature rise), so that electrons are attracted by the more attractive atomic nucleus and separated from the original atomic nucleus to form free electrons.Another reason is that due to the influence of external conditions (such as the rise of temperature), the movement ability of the electron is improved. Because the attraction ability of the atomic nucleus is realized within a certain range, the temperature increases the kinetic energy of the electron, so its movement ability is increased, and it is possible to exceed the attraction range of the atomic nucleus through movement,The electrons are separated from the atomic nucleus to form free electrons.The former reason belongs to chemical change, and the latter should belong tophysical change, because there is no formationNew substancesHowever, the formation of the latter free electron is just a complete processchemical reactionThe intermediate reaction link of.
density
Announce
edit
The number of free electrons in the conductor per unit volume isFree electron density。CopperyFree electron densityIt is 8.5 × 10 ^ 28/m ^ 3.The free electron density of various metals has the same order of magnitude.
Conductivity relationship
Announce
edit
Metal atoms are composed of positively charged protons and negatively charged electrons.Like non-metallic atoms, they are not charged as a whole.So why do metals conduct electricity?Because the attraction of the outermost electron of the metal atom nucleus is weak, there are a large number of free electrons (negative electrons) in the metalelectricUnder the action of pressure, free electrons will flow directionally, formingelectric current。Non metals, on the contrary, have very few free electrons, so they are not good at conducting electricity (although there are exceptions, such as graphite).
