Alkali metal
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224107896
2008-07-07T10:11:54Z
Nergaal
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! [[Group (periodic table)|Group]] →!! 6
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! ↓ [[Period (periodic table)|Period]]
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! [[Period 1 element|1]]
| {{element cell| 1|Hydrogen|H| |Gas|Nonmetals|Primordial}}
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! [[Period 2 element|2]]
| {{element cell| 3|Lithium|Li| |Solid|Alkali metals|Primordial}}
|-
! [[Period 3 element|3]]
| {{element cell|11|Sodium|Na| |Solid|Alkali metals|Primordial}}
|-
! [[Period 4 element|4]]
| {{element cell|19|Potassium|K| |Solid|Alkali metals|Primordial}}
|-
! [[Period 5 element|5]]
| {{element cell|37|Rubidium|Rb| |Solid|Alkali metals|Primordial}}
|-
! [[Period 6 element|6]]
| {{element cell|55|Cesium|Cs| |Solid|Alkali metals|Primordial}}
|-
! [[Period 7 element|7]]
| {{element cell|87|Francium|Fr| |Solid|Alkali metals|Natural radio}}
|}
The '''alkali metals''' are a [[chemical series|series]] of [[chemical element|elements]] comprising [[Periodic table group|Group 1]] ([[International Union of Pure and Applied Chemistry|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.
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 possess a weak radioactive characteristic (harmless) due to the presence of long duration radioactive isotopes.
The alkali metals are silver-colored (caesium has a golden tinge), soft, low-[[density]] [[metal]]s, which react readily with [[halogen]]s to form [[ionic salt]]s, and with [[water (molecule)|water]] to form strongly [[alkali]]ne [[Base (chemistry)|(basic)]] [[hydroxide]]s. 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 [[electric charge|charged]] positive [[ion]], or 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 [[halogen]]s, 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 compound]]s of hydride with the alkali metals and some [[transition metal]]s 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.
[[Image:Alkalimetalle.jpg|thumb|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) + 2H<sub>2</sub>O (l) → 2KOH (aq) + H<sub>2</sub> (g)
=== 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.
:[[Potassium|K]] + [[Ammonia|NH<sub>3</sub>]] → K<sup>+</sup> + [[Electron|e<sup>−</sup>]]
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 agent]]s and good [[conductor (electricity)|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 [[Sodium|Na]] + 2 [[Ammonia|NH<sub>3</sub>]] → 2 [[Sodium amide|NaNH<sub>2</sub>]] + [[Hydrogen|H<sub>2</sub>]]
The amide can be extracted, or it can be converted to [[sodium azide]] by bubbling [[nitrous oxide]] through the ammonia solution:
:2 [[Sodium amide|NaNH<sub>2</sub>]] + [[Nitrous oxide|N<sub>2</sub>O]] → [[Sodium azide|NaN<sub>3</sub>]] + [[Sodium hydroxide|NaOH]] + [[Ammonia|NH<sub>3</sub>]]
==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. 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.
<table border=0 cellpadding=2 cellspacing=0 width="100%">
<tr>
<td bgcolor="#CCCCFF">'''Alkali metal'''</td>
<td bgcolor="#CCCCFF" align="center">'''Standard Atomic Weight ([[unified atomic mass unit|u]])'''</td>
<td bgcolor="#CCCCFF" align="center">'''Melting Point ([[kelvin|K]])'''</td>
<td bgcolor="#CCCCFF" align="center">'''Boiling Point ([[kelvin|K]])'''</td>
<td bgcolor="#CCCCFF" align="center">'''Density ([[gram|g]]·[[centimeter|cm]]<sup>−3</sup>)'''</td>
<td bgcolor="#CCCCFF" align="center">'''Electronegativity ([[Pauling scale|Pauling]])'''</td>
</tr>
<tr>
<td>Lithium</td>
<td align="center">6.941</td>
<td align="center">453.69</td>
<td align="center">1615</td>
<td align="center">0.534</td>
<td align="center">0.98</td>
</tr>
<tr>
<td bgcolor="#EEEEEE">Sodium</td>
<td bgcolor="#EEEEEE" align="center">22.990</td>
<td bgcolor="#EEEEEE" align="center">370.87</td>
<td bgcolor="#EEEEEE" align="center">1156</td>
<td bgcolor="#EEEEEE" align="center">0.968</td>
<td bgcolor="#EEEEEE" align="center">0.93</td>
</tr>
<tr>
<td>Potassium</td>
<td align="center">39.098</td>
<td align="center">336.53</td>
<td align="center">1032</td>
<td align="center">0.89</td>
<td align="center">0.82</td>
</tr>
<tr>
<td bgcolor="#EEEEEE">Rubidium</td>
<td bgcolor="#EEEEEE" align="center">85.468</td>
<td bgcolor="#EEEEEE" align="center">312.46</td>
<td bgcolor="#EEEEEE" align="center">961</td>
<td bgcolor="#EEEEEE" align="center">1.532</td>
<td bgcolor="#EEEEEE" align="center">0.82</td>
</tr>
<tr>
<td>Caesium</td>
<td align="center">132.905</td>
<td align="center">301.59</td>
<td align="center">944</td>
<td align="center">1.93</td>
<td align="center">0.79</td>
</tr>
<tr>
<td bgcolor="#EEEEEE">Francium</td>
<td bgcolor="#EEEEEE" align="center">(223)</td>
<td bgcolor="#EEEEEE" align="center">? 295</td>
<td bgcolor="#EEEEEE" align="center">? 950</td>
<td bgcolor="#EEEEEE" align="center">? 1.87</td>
<td bgcolor="#EEEEEE" align="center">0.7</td>
</tr>
</table>
==Reference material==
* {{cite journal| author=Campbell, Linda M., Aaron T. Fisk, Xianowa Wang, Gunter Kock, and Derek C. Muir | title=Evidence for Biomagnification of Rubidium in Freshwater and Marine Food Webs | journal= Canadian Journal of Fisheries and Aquatic Sciences | volume=62 | date= 2005 | pages= 1161–1167 | doi=10.1139/f05-027}}
* {{cite book| author=Chang, Cheng-Hung, and Tian Y. Tsong | chapter=Stochastic Resonance of Na, K-Ion Pumps on the Red Cell Membrane | title= Noise and Fluctuations: 18th International Conference on Noise and Fluctuations |date= 2005 | publisher= American Institute of Physics}}
* {{cite journal | author=Sokolov, Stephen T., Russell T. Joffe, and Anthony J. Levitt | title=Lithium and Triiodothyronine Augmentation of Antidepressants | journal= Canadian Journal of Psychiatry | volume=51 | date=2006| pages= 791–793}}
* {{cite journal| author=Bauer, Brent A., Robert Houlihan, Michael J. Ackerman, Katya Johnson, and Himeshkumar Vyas | title=Acquired Long QT Syndrome Secondary to Cesium Chloride Supplement | journal= The Journal of Alternative and Complementary Medicine | volume= 12 | date=2006 | pages=1011–1014 | doi=10.1089/acm.2006.12.1011}}
* {{cite journal| author=Erermis, Serpil, Muge Tamar, Hatice Karasoy, Tezan Bildik, Eyup S. Ercan, and Ahmet Gockay| title= Zuclopenthixol-Induced Neuroleptic Malignant Syndrome in an Adolescent Girl. Clinical Toxicology. Informa Healthcare, date=2007 | pages=277–280}}
* {{cite journal| author=Sharp, Kelly | title=Hypertension: Just the Facts| journal= Clinical Journal of Oncology Nursing |volume=10| date=2006|pages= 727–729 | doi=10.1188/06.CJON.727-729}}
* {{cite journal| author=Cappacio, F P., and N D. Markandu | title=Double-Blind Randomised Trial of Modest Salt Restriction in Older People | journal= Lancet | volume=350 |date=1997| pages= 850–854 | doi=10.1016/S0140-6736(97)02264-2}}
* {{cite journal | author=Krachler, M, and E Rossipal | title=Trace Elements Transfer From Mother to the Newborn - Investigations on Triplets of Colostrum, Maternal and Umbilical Sera | journal= European Journal of Clinical Nutrition | volume=53 | date=1999| pages=486–494 | doi=10.1038/sj.ejcn.1600781}}
* "Physics Update." Physics Today June 1996: 9.
* "Visual Elements: Group 1 - The Alkali Metals." <u>Visual Elements.</u> Royal Society of Chemistry. <http://www.chemsoc.org/Viselements/pages/data/intro_groupi_data.html>.
==See also==
*[[Lithium]]
*[[Sodium]]
*[[Potassium]]
*[[Rubidium]]
*[[Caesium]]
*[[Francium]]
==External links==
*[http://www.scienceaid.co.uk/chemistry/periodictable/alkalimetals.html Science aid:Alkali metals] A simple look at alkali metals
*[http://www.wpbschoolhouse.btinternet.co.uk/page03/Alkali_Metals.htm Doc Brown, Alkali metals]
*[http://www.chemguide.co.uk/inorganic/group1/properties.html Atomic and Physical Properties of the Group 1 Elements] An in-depth look at alkali metals
{|style="text-align: center;" border="1" cellpadding="2"
|+ '''Explanation of above periodic table slice:'''
| bgcolor="{{element color/Alkali metals}}" | Alkali metals
| Atomic numbers in <font color="{{element color/Solid}}">{{element color/Solid}}</font> are solids
| style="border:{{element frame/Primordial}};" | Solid borders indicate [[primordial element]]s (older than the [[Earth]])
| style="border:{{element frame/Natural radio}};" | Dashed borders indicate natural [[radioactive decay|radioactive element]]s with no isotopes older than the Earth
|}
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