Overview
A charged particle is any particle that carries a net electric charge, positive or negative. In chemistry the term ion usually denotes an atom or molecule that has gained or lost one or more electrons, while in physics the term also covers elementary and composite particles such as the electron, proton or alpha particle. Charged particles are the carriers of electric forces and play central roles in electricity, chemistry and many technologies. For a concise definition see charged particle.
Characteristics and formation
Charged particles are characterized by their electric charge, mass and mobility. Charge is quantized in multiples of the elementary charge and may be positive or negative. An atom or molecule becomes an ion when it loses or gains electrons; this can occur through chemical reactions, collision with energetic radiation, contact electrification, or thermal ionization. Formation by chemical transfer of electrons is commonly associated with ionic bonding, but many other processes also produce charged species.
Behavior and governing principles
Charged particles interact through the electromagnetic force. Electrostatic attraction and repulsion govern how static charges arrange themselves, while motion of charges produces magnetic effects and currents. The trajectories of charged particles are influenced by electric and magnetic fields, which is the basis for devices such as cathode-ray tubes, mass spectrometers and particle beam systems. In large collections, charged particles can produce collective phenomena such as screening, plasma oscillations and instabilities.
Examples and applications
- Cations and anions in solutions and ionic crystals: essential for electrochemistry, batteries and desalination.
- Free electrons and holes in conductors and semiconductors: foundation of modern electronics and optoelectronics.
- Ions in gases and plasmas: used in fluorescent lighting, plasma processing and fusion experiments.
- Ions in mass spectrometry and ion propulsion: analytical chemistry and spacecraft propulsion respectively.
Measurement and detection
Measurements of charge, mass and energy of particles use a range of instruments. Electrometers and Faraday cups measure net charge, mass spectrometers separate ions by mass-to-charge ratio, and particle detectors register charged tracks and energies in physics experiments. Laboratory techniques for producing and studying charged particles include ion sources, vacuum chambers and beamlines.
Role in nature and technology
Charged particles are central to processes from chemical bonding and nerve impulses to atmospheric electricity and astrophysical plasmas. Technologies that rely on controlled motion of charges include electric power, semiconductor electronics, sensors, medical imaging and radiation therapy.
Distinctions and notable facts
Not every charged particle is called an ion: elementary charges such as the electron and proton are often described by their particle names. Charge is conserved in isolated systems and discrete in units of the elementary charge. For related topics and further reading see entries on charged particle, ion, atom or molecule, ionic bond and electron.