Jump to content

Alkali metal

From Wikipedia, the free encyclopedia

This is an old revision of this page, as edited by 76.253.6.158 (talk) at 18:01, 24 June 2009 (iupac spelling). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

Group → 1
↓ Period
1 1
H
2 title="Li, Lithium" style="text-align:center; color:#000000; background-color:#ff9d9d; border:2px solid #6e6e8e; ;"| 3
Li
3 title="Na, Sodium" style="text-align:center; color:#000000; background-color:#ff9d9d; border:2px solid #6e6e8e; ;"| 11
Na
4 title="K, Potassium" style="text-align:center; color:#000000; background-color:#ff9d9d; border:2px solid #6e6e8e; ;"| 19
K
5 title="Rb, Rubidium" style="text-align:center; color:#000000; background-color:#ff9d9d; border:2px solid #6e6e8e; ;"| 37
Rb
6 title="Cs, Caesium" style="text-align:center; color:#000000; background-color:#ff9d9d; border:2px solid #6e6e8e; ;"| 55
Cs
7 title="Fr, Francium" style="text-align:center; color:#000000; background-color:#ff9d9d; border:2px dashed #773300; ;"| 87
Fr

The alkali metals are a series of chemical elements comprising Group 1 (IUPAC style) of the periodic table: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr). (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.

Properties

The alkali metals are all highly reactive and are never 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 possess a weak radioactive characteristic 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, i.e. cation.

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. Their second ionization potentials are very high, as removing an electron from a species having a noble gas configuration is very difficult.

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)

Like other groups, the members of this family show patterns in its electron configuration, especially the outermost shells resulting in trends in chemical behavior:

Z Element No. of electrons/shell
1 Hydrogen 1
3 Lithium 2, 1
11 Sodium 2, 8, 1
19 Potassium 2, 8, 8, 1
37 Rubidium 2, 8, 18, 8, 1
55 Caesium 2, 8, 18, 18, 8, 1
87 Francium 2, 8, 18, 32, 18, 8, 1

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. Density generally increases, with the notable exception of potassium being less dense than sodium, and the possible exception of francium being less dense than caesium.

Alkali metal Standard Atomic Weight (u) Melting Point (K) Boiling Point (K) Density (g·cm−3) Electronegativity (Pauling)
Lithium 6.941 453 1615 0.534 0.98
Sodium 22.990 370 1156 0.968 0.93
Potassium 39.098 336 1032 0.89 0.82
Rubidium 85.468 312 961 1.532 0.82
Caesium 132.905 301 944 1.93 0.79
Francium (223) 295 950 1.87 0.70

Occurrence and production

Applications

Reference material

  • Campbell, Linda M., Aaron T. Fisk, Xianowa Wang, Gunter Kock, and Derek C. Muir (2005). "Evidence for Biomagnification of Rubidium in Freshwater and Marine Food Webs". Canadian Journal of Fisheries and Aquatic Sciences. 62: 1161–1167. doi:10.1139/f05-027.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  • Chang, Cheng-Hung, and Tian Y. Tsong (2005). "Stochastic Resonance of Na, K-Ion Pumps on the Red Cell Membrane". Noise and Fluctuations: 18th International Conference on Noise and Fluctuations. American Institute of Physics.{{cite book}}: CS1 maint: multiple names: authors list (link)
  • Sokolov, Stephen T., Russell T. Joffe, and Anthony J. Levitt (2006). "Lithium and Triiodothyronine Augmentation of Antidepressants". Canadian Journal of Psychiatry. 51: 791–793.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  • Bauer, Brent A., Robert Houlihan, Michael J. Ackerman, Katya Johnson, and Himeshkumar Vyas (2006). "Acquired Long QT Syndrome Secondary to Cesium Chloride Supplement". The Journal of Alternative and Complementary Medicine. 12: 1011–1014. doi:10.1089/acm.2006.12.1011.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  • Erermis, Serpil, Muge Tamar, Hatice Karasoy, Tezan Bildik, Eyup S. Ercan, and Ahmet Gockay (1997). "Double-Blind Randomised Trial of Modest Salt Restriction in Older People". Lancet. 350: 850–854. doi:10.1016/S0140-6736(97)02264-2.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  • Krachler, M, and E Rossipal (1999). "Trace Elements Transfer From Mother to the Newborn - Investigations on Triplets of Colostrum, Maternal and Umbilical Sera". European Journal of Clinical Nutrition. 53: 486–494. doi:10.1038/sj.ejcn.1600781.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  • "Physics Update." Physics Today June 1996: 9.

See also

Explanation of above periodic table slice:
bgcolor="Template:Element color/Alkali metals" | Alkali metals Atomic numbers in Template:Element color/Solid are solids style="border:Template:Element frame/Primordial;" | Solid borders indicate primordial elements (older than the Earth) style="border:Template:Element frame/Natural radio;" | Dashed borders indicate natural radioactive elements with no isotopes older than the Earth
Retrieved from "https://en.wikipedia.org/w/index.php?title=Alkali_metal&oldid=298399792"