cation

Examples of cation in the following topics:

• Cationic Chain-Growth Polymerization

  • Polymerization of isobutylene (2-methylpropene) by traces of strong acids is an example of cationic polymerization.
  • Monomers bearing cation stabilizing groups, such as alkyl, phenyl or vinyl can be polymerized by cationic processes.

• Ionic Radius

  • Ionic radius (rion) is the radius of an ion, regardless of whether it is an anion or a cation.
  • In this way, the sum of ionic radii of a cation and an anion can give us the distance between the ions in a crystal lattice.
  • Note that this only applies if the elements are the same type of ion, either cations or anions.
  • For example, while neutral lithium is larger than neutral fluorine, the lithium cation is much smaller than the fluorine anion, due to the lithium cation having a different highest energy shell.
  • The neutral atoms are colored gray, cations red, and anions blue.

• Characteristics of Mass Spectra

  • Loss of a hydrogen atom, either before or after ring opening, produces the stable allyl cation (m/z=41).
  • The molecular ion in a mass spectrum is always a radical cation, but the fragment ions may either be even-electron cations or odd-electron radical cations, depending on the neutral fragment lost.
  • Most of the fragment ions have odd-numbered masses, and therefore are even-electron cations.
  • The weak even -electron ions at m/z=15 and 29 are due to methyl and ethyl cations (no nitrogen atoms).
  • Bond cleavage generates a radical and a cation, and both fragments often share these roles, albeit unequally.

• Naming Ionic Compounds

  • An ionic compound is named first by its cation and then by its anion.
  • An ionic compound is named first by its cation and then by its anion.
  • The cation has the same name as its element.
  • To name a compound, the cation name and the anion named are added together.
  • Since some metallic elements form cations that have different positive charges, the names of ionic compounds derived from these elements must contain some indication of the cation charge.

• Salts that Produce Acidic Solutions

  • This is due either to the presence of a metal cation that acts as a Lewis acid (which will be discussed in a later concept), or, quite commonly, due to a hydrolyzable proton in the cation or the anion.
  • Salts with acidic protons in the cation are most commonly ammonium salts, or organic compounds that contain a protonated amine group.
  • An example of an acid salt is one containing any of these cations with a neutral base, such as ammonium chloride (NH4Cl).

• Chemical Analysis

  • Cations are usually classified into one of six groups according to their properties, while anions are classified into one of three groups.
  • Each group has a common reagent that can be used to separate the cation or anion from a solution.
  • This happens because cationic analysis is based on the solubility products of the ions.
  • As the cation achieves the optimum concentration needed, it precipitates, allowing detection.
  • (While many of the earlier cations will precipitate with carbonate, they will have been detected prior to this point if the steps have been followed in order.)

• Alteration of Membrane Permeability

  • In general, gramicidin channels are ideally selective for monovalent cations and the single-channel conductances for the alkali cations are ranked in the same order as the aqueous mobility of these ions.
  • Divalent cations like Ca2+ block the channel by binding near its mouth so that it is essentially impermeable to divalent cations, and also excludes anions.
  • Cl− in particular is excluded from the channel because its hydration shell is thermodynamically stronger than the shells of most monovalent cations.
  • The channel is permeable to most monovalent cations, which move through the channel in single file.
  • Its ability to bind and transport cations is due to the presence of cation-binding sites, one strong and the other weak, in the channel.

• Ionic Bonding and Electron Transfer

  • Ionic bonds involve a cation and an anion.
  • The bond is formed when an atom, typically a metal, loses an electron or electrons, and becomes a positive ion, or cation.
  • In this video, Paul Andersen explains how ionic solids form when cations and anions are attracted.

• Oxidation

  • When silver cation is the oxidant, as in the above equation, it is reduced to metallic silver in the course of the reaction, and this deposits as a beautiful mirror on the inner surface of the reaction vessel.
  • The Fehling and Benedict tests use cupric cation as the oxidant.
  • All these cation oxidations must be conducted under alkaline conditions.
  • To avoid precipitation of the insoluble metal hydroxides, the cations must be stabilized as complexed ions.

• Complex Ion Equilibria and Solubility

  • Formation of a complex ion between a metal cation and a ligand can increase salt solubility.
  • A complex ion is an ion comprising one or more ligands attached to a central metal cation with a dative bond.
  • Cations of d-block metals (transition metals) are small, have a high charge, and have available empty 3d and 4s orbitals of low energy.
  • The number of lone pairs of electrons a cation can accept is known as the coordination number of the cation.
  • This number depends on the size and electronic configuration of that cation and on the size and charge of the ligand.