electric current & its particles: electrons
Fig. 1. Classical picture of an atom: Electrons orbit the atomic core like planets orbit the sun. (© ch)
Electric current is the flow of electric charge. Its unit is 1 ampere (1 A), which in the International System of Units (SI)
is one of the four basic units: meter, kilogram, second, and ampere. The units of all other physical quantities can be derived from these units by using the physical laws of nature. Electric current is transported by particles, called electrons. Electrons are elementary (i.e. indivisible) particles, the size of which has proven immeasurably small up to now, but its charge and mass are precisely known, see box. The small value of the electron’s charge implies that within one second some 10^{19} electrons flow across a wire which transports a current of 1.6 A. Such a flow is only possible if there are electrons that are very weakly bound to atoms so that they can move freely between atoms. This is the case in metals.
is one of the four basic units: meter, kilogram, second, and ampere. The units of all other physical quantities can be derived from these units by using the physical laws of nature. Electric current is transported by particles, called electrons. Electrons are elementary (i.e. indivisible) particles, the size of which has proven immeasurably small up to now, but its charge and mass are precisely known, see box. The small value of the electron’s charge implies that within one second some 10^{19} electrons flow across a wire which transports a current of 1.6 A. Such a flow is only possible if there are electrons that are very weakly bound to atoms so that they can move freely between atoms. This is the case in metals.
The SI unit of electric charge is 1 coulomb = 1 ampere x 1 second.
The charge of an electron is e = -1.6 \times 10^{-19} coulomb. The charge
transported by a current of 1 ampere in 1 second. It is known as
the smallest, indivisible (i.e. elementary) unit of charge.
The electron's rest mass is m_e = 9.1 \times 10^{-31} kg, a number with thirty zeros behind the decimal point.
The electron's rest mass is m_e = 9.1 \times 10^{-31} kg, a number with thirty zeros behind the decimal point.
Electrons – together with the positively-charged protons – form atoms and bind atoms to each other to form molecules, the smallest unit of matter that is able to perform biological functions enabling life. The microscopic states and motion of electrons obey the laws of quantum physics
. These laws dictate that the electron’s quantum state is described by a wavefunction, which is a number rapidly varying in space and time. The square of this number gives the probability with which the electron can be found at any position in space, its spatial distribution can be imagined as a “cloud”. In atomic quantum states, the electron cloud is localized near the atomic core. Atoms are glued together to form a molecule by electrons occupying molecular quantum states, characterized by an electron cloud surrounding two or more atoms forming the molecule.
. These laws dictate that the electron’s quantum state is described by a wavefunction, which is a number rapidly varying in space and time. The square of this number gives the probability with which the electron can be found at any position in space, its spatial distribution can be imagined as a “cloud”. In atomic quantum states, the electron cloud is localized near the atomic core. Atoms are glued together to form a molecule by electrons occupying molecular quantum states, characterized by an electron cloud surrounding two or more atoms forming the molecule.
Fig. 2. Quantummechanic view on atoms: Electrons have a certain probability that they can be found in the vicinity of the core. As a consequence of the uncertainty principle an electron does not have a defined trajectory. In this image a 1S and a 2S orbital is shown. (© ch)
Fig. 3. Building a molecule: When two ore more atoms are brought together the probability distributions of the electrons change. If it is energetically beneficial molecular orbitals form around 2 or more atomic cores. (© ch)
further reading
The quantitative development of electricity began late in the 18th century. J.B. Priestley in 1767 and C.A. Coulomb in 1875 discovered indepently the inverse-square law for stationary charges. This law still serves as a foundation for electrostatics.
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