ion

Physiology

(noun)

An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge.

Related Terms

  • transcellular fluid
  • resting membrane potential
  • Goldman equation
  • electrolyte
Chemistry

(noun)

An atom or group of atoms bearing an electrical charge, such as the sodium and chlorine atoms in a salt solution.

Related Terms

  • Hydration
  • ion-induced dipole force
  • dipole
  • zwitterion
  • ion-dipole forces
  • dipole-dipole forces
  • electron cloud
  • thermodynamics
  • heat of hydration
  • anion
  • cation

(noun)

An atom or group of atoms bearing an electrical charge, such as sodium and chlorine in table salt.

Related Terms

  • Hydration
  • ion-induced dipole force
  • dipole
  • zwitterion
  • ion-dipole forces
  • dipole-dipole forces
  • electron cloud
  • thermodynamics
  • heat of hydration
  • anion
  • cation

Examples of ion in the following topics:

  • Ion-Dipole Force

    • The ion-dipole force is an intermolecular attraction between an ion and a polar molecule.
    • However, ion-dipole forces involve ions instead of solely polar molecules.
    • Ion-dipole forces are stronger than dipole interactions because the charge of any ion is much greater than the charge of a dipole; the strength of the ion-dipole force is proportionate to ion charge.
    • An ion-induced dipole force occurs when an ion interacts with a non-polar molecule.
    • Ion-dipole forces are generated between polar water molecules and a sodium ion.
  • Lewis Structures for Polyatomic Ions

    • Lewis structures for polyatomic ions are drawn by the same methods that we have already learned.
    • When counting electrons, negative ions should have extra electrons placed in their Lewis structures; positive ions should have fewer electrons than an uncharged molecule.
    • Negative ions follow the same procedure.
    • The chlorite ion, ClO2–, contains 19 (7 from the Cl and 6 from each of the two O atoms) +1 = 20 electrons.
    • The hypochlorite ion, ClO−, contains 13 + 1 = 14 electrons.
  • Characteristics of Mass Spectra

    • The highest-mass ion in a spectrum is normally considered to be the molecular ion, and lower-mass ions are fragments from the molecular ion, assuming the sample is a single pure compound.
    • The molecular ion is the strongest ion in the spectra of CO2 and C3H6, and it is moderately strong in propane.
    • The molecular ion is also the base peak, and the only fragment ions are CO (m/z=28) and O (m/z=16).
    • The molecular ion of propane also has m/z=44, but it is not the most abundant ion in the spectrum.
    • As a rule, odd-electron ions may fragment either to odd or even-electron ions, but even-electron ions fragment only to other even-electron ions.
  • The Common Ion Effect

    • The common ion effect describes the changes that occur with the introduction of ions to a solution containing that same ion.
    • The common ion effect can be explained by Le Chatelier's principle of chemical equilibrium:
    • For a simple dissolution process, the addition of more of one of the ions (A+) from another compound will shift the composition to the left, reducing the concentration of the other ion (B-), effectively reducing the solubility of the solid (AB).
    • Addition of excess ions will alter the pH of the buffer solution.
    • Therefore, the common ion effect takes a role in pH regulation.
  • Ion Channels

    • Ion channels are membrane proteins that allow ions to travel into or out of a cell.
    • Most channels are specific (selective) for one ion.
    • When a channel is open, ions permeate through the channel pore down the transmembrane concentration gradient for that particular ion.
    • Ion pumps are not ion channels, but are critical membrane proteins that carry out active transport by using cellular energy (ATP) to "pump" the ions against their concentration gradient.
    • A schematic representation of an ion channel.
  • Chemiosmosis and Oxidative Phosphorylation

    • Chemiosmosis is the movement of ions across a selectively permeable membrane, down their electrochemical gradient.
    • The uneven distribution of H+ ions across the membrane establishes both concentration and electrical gradients (thus, an electrochemical gradient) owing to the hydrogen ions' positive charge and their aggregation on one side of the membrane.
    • If the membrane were open to diffusion by the hydrogen ions, the ions would tend to spontaneously diffuse back across into the matrix, driven by their electrochemical gradient.
    • However, many ions cannot diffuse through the nonpolar regions of phospholipid membranes without the aid of ion channels.
    • At the end of the pathway, the electrons are used to reduce an oxygen molecule to oxygen ions.
  • The Lithium-Ion Battery

    • Lithium-ion batteries (Li-ion batteries, or LIBs) are a family of rechargeable batteries in which lithium ions move from the negative electrode to the positive electrode during discharge.
    • The ions follow the reverse path when the battery is charging.
    • Li-ion batteries use a lithium compound as the electrode material.
    • Lithium-ion batteries are common in consumer electronics.
    • In a lithium-ion battery, the lithium ions are transported to and from the cathode or anode.
  • The Mass Spectrometer

    • The heart of the spectrometer is the ion source.
    • Some of these ions fragment into smaller cations and neutral fragments.
    • A perpendicular magnetic field deflects the ion beam in an arc whose radius is inversely proportional to the mass of each ion.
    • Lighter ions are deflected more than heavier ions.
    • Residual energy from the collision may cause the molecular ion to fragment into neutral pieces (colored green) and smaller fragment ions (colored pink and orange).
  • Ionic Crystals

    • other combinations of sodium, cesium, rubidium, or lithium ions with fluoride, bromide, chloride or iodide ions
    • The exact arrangement of ions in a lattice varies according to the size of the ions in the crystal.
    • Structurally, each ion in sodium chloride is surrounded by six neighboring ions of opposite charge.
    • In CsCl, metal ions are shifted into the center of each cubic element of the Cl–-ion lattice.
    • Each cesium ion has eight nearest-neighbor chloride ions, while each chloride ion is also surrounded by eight cesium ions in (8,8) coordination.
  • Formulas of Ionic Compounds

    • Its ionic formula is written as CaCl2, the neutral combination of these ions.
    • Polyatomic ions are a set of covalently bonded atoms that have an overall charge, making them an ion.
    • For example, the hydroxide ion has the formula OH-1.
    • When creating ionic compounds with these polyatomic ions, treat them the same way as typical monatomic ions (only one atom).
    • This video shows you how monoatomic ions get their charge, and how to quickly find the charge of ions by looking at the periodic table.
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