Alkali metal

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Group 1
Period
1 1
H
2 3
Li
3 11
Na
4 19
K
5 37
Rb
6 55
Cs
7 87
Fr

The alkali metals are a series of elements comprising Group 1 (IUPAC style) of the periodic table: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr). (Note that hydrogen, although nominally also a member of Group 1, very rarely exhibits behavior comparable to the alkali metals). The alkali metals provide one of the best examples of group trends in properties in the periodic table, with well characterized homologous behavior down the group.

The alkali metals are all highly reactive and are rarely found in elemental form in nature. As a result, in the laboratory they are stored under mineral oil. They also tarnish easily and have low melting points and densities. Potassium and Rubidium are very weakly radioactive (harmless) due to the presence of long duration radioactive isotopes.

The alkali metals are silver-colored (caesium has a golden tinge), soft, low-density metals, which react readily with halogens to form ionic salts, and with water to form strongly alkaline (basic) hydroxides. These elements all have one electron in their outermost shell, so the energetically preferred state of achieving a filled electron shell is to lose one electron to form a singly charged positive ion.

Hydrogen, with a solitary electron, is usually placed at the top of Group 1 of the periodic table, but it is not considered an alkali metal; rather it exists naturally as a diatomic gas. Removal of its single electron requires considerably more energy than removal of the outer electron for the alkali metals. As in the halogens, only one additional electron is required to fill in the outermost shell of the hydrogen atom, so hydrogen can in some circumstances behave like a halogen, forming the negative hydride ion. Binary compounds of hydride with the alkali metals and some transition metals have been prepared. Under extremely high pressure, such as is found at the core of Jupiter, hydrogen does become metallic and behaves like an alkali metal; see metallic hydrogen.

Alkali metals have the lowest ionization potentials in their respective periods, as removing the single electron from the outermost shell gives them the stable inert gas configuration. But their second ionization potentials are very high, as removing an electron from a species having a noble gas configuration is very difficult.

Contents

  • 1 Reactions
    • 1.1 Reactions in water
    • 1.2 Reaction in ammonia
  • 2 Trends
  • 3 Biological occurrences
  • 4 Reference Material
  • 5 See also
  • 6 External links

[edit] Reactions

[edit] Reactions in water

Series of alkali metals, stored in mineral oil (note "natrium" is sodium.)

Alkali metals are famous for their vigorous reactions with water, and these reactions become increasingly violent as one moves down the group. The reaction with water is as follows:

Alkali metal + water → Alkali metal hydroxide + hydrogen gas

With potassium as an example:

2K (s) + 2H2O (l) → 2KOH (aq) + H2 (g)

In this reaction, enough energy is produced to ignite the hydrogen, creating a lilac flame above the potassium. If rubidium or caesium react with water though, the subsequent explosion tends to be very violent, a fact not helped by its rapidity in coming about once the metal and water start reacting.

[edit] Reaction in ammonia

Alkali metals dissolve in liquid ammonia to give blue solutions that are paramagnetic. As the solution approaches saturation, it becomes deep purple, then metallic.

K + NH3 → K+ + e-

Because the solution contains free electrons, it occupies more space than the sum of the volumes of the metal and ammonia. The presence of free electrons also makes these solutions very good reducing agents and good electrical conductors. Since they are easier to handle than the metals themselves they are sometimes used as substitutes.

The solution is not stable over long periods, and the dissolved alkali metal will react to form the corresponding amide. This reaction, when accelerated with a catalyst (usually iron(III) nitrate), is used for the production of sodium amide:

2 Na + 2 NH3 → 2 NaNH2 + H2

The amide can be extracted, or it can be converted to sodium azide by bubbling nitrous oxide through the ammonia solution:

2 NaNH2 + N2O → NaN3 + NaOH + NH3

[edit] Trends

The alkali metals show a number of trends when moving down the group - for instance, decreasing electronegativity, increasing reactivity, and decreasing melting and boiling point.

Alkali metal Standard Atomic Weight (u) Melting Point (K) Boiling Point (K) Electronegativity (Pauling)
Lithium 6.941 453.69 1615 0.98
Sodium 22.990 370.87 1156 0.93
Potassium 39.098 336.53 1032 0.82
Rubidium 85.468 312.46 961 0.82
Caesium 132.905 301.59 944 0.79
Francium (223) ? 295 ? 950 0.7

[edit] Biological occurrences

[edit] Reference Material

Campbell, Linda M., Aaron T. Fisk, Xianowa Wang, Gunter Kock, and Derek C. Muir. "Evidence for Biomagnification of Rubidium in Freshwater and Marine Food Webs." Canadian Journal of Fisheries and Aquatic Sciences 62 (2005): 1161-1167. Academic Search Elite. EBSCO. McIntyre Library, Eau Claire. 1 May 2007 <http://web.ebscohost.com/ehost/detail?vid=4&hid=108&sid=0795c290-e438-449b-a713-f035a2e12aa4%40sessionmgr109>.

Chang, Cheng-Hung, and Tian Y. Tsong. Stochastic Resonance of Na, K-Ion Pumps on the Red Cell Membrane. Noise and Fluctuations: 18th International Conference on Noise and Fluctuations, 2005, American Institute of Physics. 30 Apr. 2007 <http://web.ebscohost.com/ehost/detail?vid=11&hid=108&sid=0795c290-e438-449b-a713-f035a2e12aa4%40sessionmgr109>.

Sokolov, Stephen T., Russell T. Joffe, and Anthony J. Levitt. "Lithium and Triiodothyronine Augmentation of Antidepressants." Canadian Journal of Psychiatry 51 (2006): 791-793. Academic Search Elite. EBSCO. McIntyre Library, Eau Claire. 29 Apr. 2007 <http://web.ebscohost.com/ehost/detail?vid=7&hid=108&sid=0795c290-e438-449b-a713-f035a2e12aa4%40sessionmgr109>.

Bauer, Brent A., Robert Houlihan, Michael J. Ackerman, Katya Johnson, and Himeshkumar Vyas. "Acquired Long QT Syndrome Secondary to Cesium Chloride Supplement." The Journal of Alternative and Complementary Medicine 12 (2006): 1011-1014. Academic Search Elite. EBSCO. McIntyre Library, Eau Claire. 3 May 2007 <http://web.ebscohost.com/ehost/detail?vid=14&hid=108&sid=0795c290-e438-449b-a713-f035a2e12aa4%40sessionmgr109>.

Erermis, Serpil, Muge Tamar, Hatice Karasoy, Tezan Bildik, Eyup S. Ercan, and Ahmet Gockay. Zuclopenthixol-Induced Neuroleptic Malignant Syndrome in an Adolescent Girl. Clinical Toxicology. Informa Healthcare, 2007. 277-280. 6 May 2007 <http://web.ebscohost.com/ehost/detail?vid=23&hid=108&sid=0795c290-e438-449b-a713-f035a2e12aa4%40sessionmgr109>.

Sharp, Kelly. "Hypertension: Just the Facts." Ed. Joyce A. Marrs. Clinical Journal of Oncology Nursing 10 (2006): 727-729. Academic Search Elite. EBSCO. McIntyre Library, Eau Claire. 8 May 2007 <http://web.ebscohost.com/ehost/detail?vid=26&hid=108&sid=0795c290-e438-449b-a713-f035a2e12aa4%40sessionmgr109>.

Cappacio, F P., and N D. Markandu. "Double-Blind Randomised Trial of Modest Salt Restriction in Older People." Lancet 350 (1997): 850-854. Academic Search Elite. EBSCO. McIntyre Library, Eau Claire. 6 Mar. 2007 <http://web.ebscohost.com/ehost/detail?vid=29&hid=108&sid=0795c290-e438-449b-a713-f035a2e12aa4%40sessionmgr109>.

Krachler, M, and E Rossipal. "Trace Elements Transfer From Mother to the Newborn - Investigations on Triplets of Colostrum, Maternal and Umbilical Sera." European Journal of Clinical Nutrition 53 (1999): 486-494. EBSCO. McIntyre Library, Eau Claire. 9 May 2007 <http://web.ebscohost.com/ehost/detail?vid=47&hid=108&sid=0795c290-e438-449b-a713-f035a2e12aa4%40sessionmgr109>.

"Physics Update." Physics Today June 1996: 9. Academic Search Elite. EBSCO. McIntyre Library, Eau Claire. 9 May 2007 <http://web.ebscohost.com/ehost/detail?vid=56&hid=108&sid=0795c290-e438-449b-a713-f035a2e12aa4%40sessionmgr109>.

"Visual Elements: Group 1 - The Alkali Metals." Visual Elements. Royal Society of Chemistry. <http://www.chemsoc.org/Viselements/pages/data/intro_groupi_data.html>.