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The alkali metal peroxides are ionic compounds that are unstable in water. The peroxide anion is weakly bound to the cation, and it is hydrolysed, forming stronger covalent bonds. |
Na2O2 + 2H2O → 2NaOH + H2O2 |
The other oxygen compounds are also unstable in water. |
2KO2 + 2H2O → 2KOH + H2O2 + O2 |
Li2O + H2O → 2LiOH |
Reaction with sulfur |
With sulfur, they form sulfides and polysulfides. |
2Na + 1/8S8 → Na2S + 1/8S8 → Na2S2...Na2S7 |
Because alkali metal sulfides are essentially salts of a weak acid and a strong base, they form basic solutions. |
S2- + H2O → HS− + HO− |
HS− + H2O → H2S + HO− |
Reaction with nitrogen |
Lithium is the only metal that combines directly with nitrogen at room temperature. |
3Li + 1/3N2 → Li3N |
Li3N can react with water to liberate ammonia. |
Li3N + 3H2O → 3LiOH + NH3 |
Reaction with hydrogen |
With hydrogen, alkali metals form saline hydrides that hydrolyse in water. |
Na + H2 → NaH (at high temperatures) |
NaH + H2O → NaOH + H2 |
Reaction with carbon |
Lithium is the only metal that reacts directly with carbon to give dilithium acetylide. Na and K can react with acetylene to give acetylides. |
2Li + 2C → Li2C2 |
Na + C2H2 → NaC2H + 1/2H2 (at 1500C) |
Na + NaC2H → Na2C2 (at 2200C) |
Reaction with water |
On reaction with water, they generate hydroxide ions and hydrogen gas. This reaction is vigorous and highly exothermic and the hydrogen resulted may ignite in air or even explode in the case of Rb and Cs. |
Na + H2O → NaOH + 1/2H2 |
Reaction with other salts |
The alkali metals are very good reducing agents. They can reduce metal cations that are less electropositive. Titanium is produced industrially by the reduction of titanium tetrachloride with Na at 4000C (van Arkel–de Boer process). |
TiCl4 + 4Na → 4NaCl + Ti |
Reaction with organohalide compounds |
Alkali metals react with halogen derivatives to generate hydrocarbon via the Wurtz reaction. |
2CH3-Cl + 2Na → H3C-CH3 + 2NaCl |
Alkali metals in liquid ammonia |
Alkali metals dissolve in liquid ammonia or other donor solvents like aliphatic amines or hexamethylphosphoramide to give blue solutions. These solutions are believed to contain free electrons. |
Na + xNH3 → Na+ + e(NH3)x− |
Due to the presence of solvated electrons, these solutions are very powerful reducing agents used in organic synthesis. |
Reaction 1) is known as Birch reduction. |
Other reductions that can be carried by these solutions are: |
S8 + 2e− → S82- |
Fe(CO)5 + 2e− → Fe(CO)42- + CO |
Extensions |
Although francium is the heaviest alkali metal that has been discovered, there has been some theoretical work predicting the physical and chemical characteristics of hypothetical heavier alkali metals. Being the first period 8 element, the undiscovered element ununennium (element 119) is predicted to be the next alkali... |
The stabilisation of ununennium's valence electron and thus the contraction of the 8s orbital cause its atomic radius to be lowered to 240 pm, very close to that of rubidium (247 pm), so that the chemistry of ununennium in the +1 oxidation state should be more similar to the chemistry of rubidium than to that of franci... |
Not as much work has been done predicting the properties of the alkali metals beyond ununennium. Although a simple extrapolation of the periodic table (by the aufbau principle) would put element 169, unhexennium, under ununennium, Dirac-Fock calculations predict that the next element after ununennium with alkali-metal-... |
The probable properties of further alkali metals beyond unsepttrium have not been explored yet as of 2019, and they may or may not be able to exist. In periods 8 and above of the periodic table, relativistic and shell-structure effects become so strong that extrapolations from lighter congeners become completely inaccu... |
Pseudo-alkali metals |
Many other substances are similar to the alkali metals in their tendency to form monopositive cations. Analogously to the pseudohalogens, they have sometimes been called "pseudo-alkali metals". These substances include some elements and many more polyatomic ions; the polyatomic ions are especially similar to the alkali... |
Hydrogen |
The element hydrogen, with one electron per neutral atom, is usually placed at the top of Group 1 of the periodic table for convenience, but hydrogen is not normally considered to be an alkali metal; when it is considered to be an alkali metal, it is because of its atomic properties and not its chemical properties. Und... |
Hydrogen, like the alkali metals, has one valence electron and reacts easily with the halogens, but the similarities mostly end there because of the small size of a bare proton H+ compared to the alkali metal cations. Its placement above lithium is primarily due to its electron configuration. It is sometimes placed abo... |
The first ionisation energy of hydrogen (1312.0 kJ/mol) is much higher than that of the alkali metals. As only one additional electron is required to fill in the outermost shell of the hydrogen atom, hydrogen often behaves like a halogen, forming the negative hydride ion, and is very occasionally considered to be a hal... |
The 1s1 electron configuration of hydrogen, while analogous to that of the alkali metals (ns1), is unique because there is no 1p subshell. Hence it can lose an electron to form the hydron H+, or gain one to form the hydride ion H−. In the former case it resembles superficially the alkali metals; in the latter case, the... |
Ammonium and derivatives |
The ammonium ion () has very similar properties to the heavier alkali metals, acting as an alkali metal intermediate between potassium and rubidium, and is often considered a close relative. For example, most alkali metal salts are soluble in water, a property which ammonium salts share. Ammonium is expected to behave ... |
Other "pseudo-alkali metals" include the alkylammonium cations, in which some of the hydrogen atoms in the ammonium cation are replaced by alkyl or aryl groups. In particular, the quaternary ammonium cations () are very useful since they are permanently charged, and they are often used as an alternative to the expensiv... |
Cobaltocene and derivatives |
Cobaltocene, Co(C5H5)2, is a metallocene, the cobalt analogue of ferrocene. It is a dark purple solid. Cobaltocene has 19 valence electrons, one more than usually found in organotransition metal complexes, such as its very stable relative, ferrocene, in accordance with the 18-electron rule. This additional electron occ... |
Thallium |
Thallium is the heaviest stable element in group 13 of the periodic table. At the bottom of the periodic table, the inert pair effect is quite strong, because of the relativistic stabilisation of the 6s orbital and the decreasing bond energy as the atoms increase in size so that the amount of energy released in forming... |
Copper, silver, and gold |
The group 11 metals (or coinage metals), copper, silver, and gold, are typically categorised as transition metals given they can form ions with incomplete d-shells. Physically, they have the relatively low melting points and high electronegativity values associated with post-transition metals. "The filled d subshell an... |
In Mendeleev's 1871 periodic table, copper, silver, and gold are listed twice, once under group VIII (with the iron triad and platinum group metals), and once under group IB. Group IB was nonetheless parenthesised to note that it was tentative. Mendeleev's main criterion for group assignment was the maximum oxidation s... |
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