An alkalide is a

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

in which alkali metal atoms are

anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

s (negative ions) with a

charge Charge or charged may refer to: Arts, entertainment, and media Films * '' Charge, Zero Emissions/Maximum Speed'', a 2011 documentary Music * ''Charge'' (David Ford album) * ''Charge'' (Machel Montano album) * ''Charge!!'', an album by The Aqu ...

oxidation state In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. C ...

of −1. Until the first discovery of alkalides in the 1970s, alkali metals were known to appear in

salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quant ...

s only as cations (positive ions) with a charge or oxidation state of +1. These types of compounds are of theoretical interest due to their unusual stoichiometry and low

ionization potential Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule ...

s. Alkalide compounds are chemically related to the electrides, salts in which trapped electrons are effectively the anions.

"Normal" alkali metal compounds

Alkali metals form many well-known stable salts. Sodium chloride (common table salt), , illustrates the usual role of an alkali metal such as sodium. In the

empirical formula In chemistry, the empirical formula of a chemical compound is the simplest whole number ratio of atoms present in a compound. A simple example of this concept is that the empirical formula of sulfur monoxide, or SO, would simply be SO, as is the ...

for this ionic compound, the positively charged

sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable ...

ion is balanced by a negatively charged

chloride The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride sa ...

ion. The traditional explanation for stable is that the loss of one

electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no ...

from elemental sodium to produce a cation with charge of +1 produces a stable closed-shell electron configuration.

Nomenclature and known cases

There are known alkalides for some of the alkali metals: *Sodide or natride, *Potasside or kalide, *Rubidide, *Caeside, Alkalides of the other alkali metals have not yet been discovered: *Lithide, *Francide,

Examples

Normally, alkalides are thermally labile due to the high reactivity of the alkalide anion, which is theoretically able to break most covalent bonds including the

carbon–oxygen bond A carbon–oxygen bond is a polar covalent bond between atoms of carbon and oxygen. Carbon–oxygen bonds are found in many inorganic compounds such as carbon oxides and oxohalides, carbonates and metal carbonyls, and in organic compounds such as ...

s in a typical

cryptand In chemistry, cryptands are a family of synthetic, bicyclic and polycyclic, multidentate ligands for a variety of cations. The Nobel Prize for Chemistry in 1987 was given to Donald J. Cram, Jean-Marie Lehn, and Charles J. Pedersen for their ...

. The introduction of a special cryptand ligand containing amines instead of ether linkages has allowed the isolation of kalides and natrides that are stable at room temperature. Several alkalides have been synthesized: *A compound in which hydrogen ions are encapsulated by

adamanzane Adamanzanes (abbreviated ''Adz'') are compounds containing four nitrogen atoms linked by carbons (analogous to adamantane with nitrogen at the branched position). Often coordinated to a central ligand, the nitrogens occupy the vertices of a tetr ...

, known as hydrogen natride or "inverse sodium hydride" (), has been observed. *Sodium-crypt natride, cryptand[2.2.2.html"_;"title="2.2.2-Cryptand.html"_;"title="a(2.2.2-Cryptand">cryptand[2.2.2">2.2.2-Cryptand.html"_;"title="a(2.2.2-Cryptand">cryptand[2.2.2.html" ;"title="2.2.2-Cryptand">cryptand[2.2.2.html" ;"title="2.2.2-Cryptand.html" ;"title="a(2.2.2-Cryptand">cryptand[2.2.2">2.2.2-Cryptand.html" ;"title="a(2.2.2-Cryptand">cryptand[2.2.2">2.2.2-Cryptand">cryptand[2.2.2.html" ;"title="2.2.2-Cryptand.html" ;"title="a(2.2.2-Cryptand">cryptand[2.2.2">2.2.2-Cryptand.html" ;"title="a(2.2.2-Cryptand">cryptand[2.2.2sup>+Na⁻, has been observed. This salt contains both and . The

isolates and stabilizes the , preventing it from being reduced by the . *Barium azacryptand-sodide, Ba²⁺(H₅Azacryptand[2.2.2]⁻)Na⁻⋅2MeNH₂, has been synthesized. *Dimer (chemistry), Dimers of cationic and anionic sodium have been observed.

References

{{Caesium compounds Sodium compounds Potassium compounds Rubidium compounds Caesium compounds Anions Alkali metals