electron volt

Examples of electron volt in the following topics:

• The Electron-Volt

  • The electron volt is a unit of energy useful in the physics of elementary charges and electricity.
  • The electron volt is defined as the amount of energy gained or lost by the charge of an electron moved across a one-volt electric potential difference.
  • Not an SI unit in itself, the electron volt became useful through experimentation.
  • Given that mass is equivalent to energy, the electron volt can measure mass.
  • In plasma physics, the electron volt can be used as a unit of temperature.

• Ionization Energy

  • This property is also referred to as the ionization potentia and is measured in volts.
  • In atomic physics, the ionization energy is typically measured in the unit electron volt (eV).
  • More generally, the nth ionization energy is the energy required to strip off the nth electron after the first n-1 electrons have been removed.
  • It is considered a measure of the tendency of an atom or ion to surrender an electron or the strength of the electron binding.
  • This graph shows the first ionization energy of the elements in electron volts.

• Electromagnetic Spectrum

  • Photon energy is directly proportional to the wave frequency, so gamma ray photons have the highest energy (around a billion electron volts), while radio wave photons have very low energy (around a femto-electron volt).
  • An example would be the oscillation of the electrons in an antenna.
  • Visible: Molecular electron excitation (including pigment molecules found in the human retina), plasma oscillations (in metals only).
  • Ultraviolet: Excitation of molecular and atomic valence electrons, including ejection of the electrons (photoelectric effect).
  • X-rays: Excitation and ejection of core atomic electrons, Compton scattering (for low atomic numbers).

• Standard Reduction Potentials

  • Reduction potential (also known as redox potential, oxidation/reduction potential, or Eh) measures the tendency of a chemical species to acquire electrons and thereby be reduced.
  • Reduction potential is measured in volts (V) or millivolts (mV).
  • The more positive the potential, the greater the species' affinity for electrons, or the more the species tends to be reduced.
  • The standard reduction potential is defined relative to a standard hydrogen electrode (SHE) reference electrode, which is arbitrarily given a potential of 0.00 volts.

• The Battery

  • In the redox (reduction-oxidation) reaction that powers the battery, cations are reduced (electrons are added) at the cathode, while anions are oxidized (electrons are removed) at the anode.
  • The electrical driving force across the terminals of a cell is known as the terminal voltage (difference) and is measured in volts.
  • When a battery is connected to a circuit, the electrons from the anode travel through the circuit toward the cathode in a direct circuit.
  • When it is connected to a circuit, that electric potential is converted to kinetic energy as the electrons travel through the circuit.
  • This orientation is important when drawing circuit diagrams to depict the correct flow of electrons.

• Free Energy and Cell Potential

  • The basis for an electrochemical cell, such as the galvanic cell, is always a redox reaction that can be broken down into two half-reactions: oxidation occurs at the anode, where there is a loss of electrons, and reduction occurs at the cathode, where there is a gain of electrons.
  • Here, n is the number of moles of electrons and F is the Faraday constant (96,485$\frac {Coulombs}{mole}$).
  • The number of moles of electrons transferred is 2, while the cell potential is equal to 0.12 V.
  • One volt is $1\frac {Joule}{Coulomb}$.
  • Electrons flow in the external circuit.

• Sources of EMF

  • Electromotive force, also called EMF (denoted and measured in volts) refers to voltage generated by a battery or by the magnetic force according to Faraday's Law of Induction, which states that a time varying magnetic field will induce an electric current.
  • Electromotive "force" is not considered a force (as force is measured in newtons) but a potential, or energy per unit of charge, measured in volts.
  • Charge separation takes place within the generator, with electrons flowing away from one terminal and toward the other, until, in the open-circuit case, sufficient electric field builds up to make further movement unfavorable.

• Electrolytic Properties

  • Lone electrons cannot usually pass through the electrolyte; instead, a chemical reaction occurs at the cathode that consumes electrons from the anode.
  • Another reaction occurs at the anode, producing electrons that are eventually transferred to the cathode.
  • In batteries for example, two materials with different electron affinities are used as electrodes: outside the battery, electrons flow from one electrode to the other; inside, the circuit is closed by the electrolyte's ions.
  • The mnemonic "LeO said GeR" is useful for remembering "lose an electron in oxidation" and "gain an electron in reduction."
  • This is the standard reduction potential for the reaction shown, measured in volts.

• Conductors

  • In metallic conductors such as copper or aluminum, the movable charged particles are electrons.
  • Band theory models the behavior of electrons in solids by postulating the existence of energy bands.
  • This produces a number of molecular orbitals proportional to the number of valence electrons.
  • All conductors contain electrical charges, which will move when an electric potential difference (measured in volts) is applied across separate points on the material.
  • For instance, the sea of electrons causes most metals to act both as electrical and thermal conductors.

• Fuel Cells

  • Electrons are drawn from the anode to the cathode through an external circuit, producing direct-current electricity.
  • Individual fuel cells produce relatively small electrical potentials, about 0.7 volts, so cells are "stacked," or placed in series, to increase the voltage.
  • The electrolyte is a substance that is specifically designed so that ions can pass through it but electrons cannot.
  • The freed electrons travel through a wire, creating the electric current.
  • There, the ions are reunited with the electrons, and the two react with a third chemical, usually oxygen, to create water or carbon dioxide.