Alkali metal

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 [hide]
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
The alkali metal lithium is not essential for any biological functions, but was found to exist in extremely tiny quantities in umbilical cord blood. This was found during a study by taking blood samples of newborns from both the umbilical cord and the mother at the time of birth, and subjecting the samples to a number of tests. They found that there was 7 times the amount of lithium in blood than previously believed. (Krachler and Rossipal 488) While it is considered a non-essential trace element (an element needed in extremely tiny amounts for proper growth), lithium also has medicinal uses. A double-blind, placebo-controlled, two-week long study conducted by a group of doctors on severely depressed patients proved that lithium is a key component in the treatment of severe depression. (Joffe, Levitt, and Sokolov, 791) It has also been proven to play a role in the treatment of other mental disorders. (Bildik et al. 277) One recorded instance was the case of a girl who developed a condition known as Neuroleptic malignant syndrome, who was given an antipsychotic drug (a tranquilizing drug that induces a state of relative calm). She quickly developed the symptoms of NMS, and was quickly hospitalized. There, doctors began treating her for the disorder, and in the final stage of her treatment, lithium was administered to her to help stabilize her mental functions. Weeks later, she was released and was in good physical health, but retained her previous diagnosis of Bipolar Disorder (a mental disorder that encompasses periods of mania and depression interspersed by periods of normal behavior). (Bildik et al. 278)
Sodium and potassium are very common alkali metals. These elements are essential for the existence of all known life. They are found in the cytoplasm (organic fluid, mainly water) of all living cells, and they are critical to everyday cell operation and regulation. (Chang and Tsong 587) Also, a common sodium salt, sodium chloride (table salt), has been identified many times as a contributor to hypertension in humans. (Sharp 727) A double-blind, two-month study was conducted on a group of elderly adults by modestly cutting their salt intake, to find if cutting salt intake would lower blood pressure. Some in the group were given half the salt that others were given for the duration of the study. The findings indicated that those who were given only half the amount of salt experienced a drop in blood pressure of up to 7.2 mm Hg (millimeters Mercury). (Cappacio and Markandu 850)
Rubidium is not required for any known biological functions, but is known to be an unnecessary and toxic trace-element in humans. (Krachler and Rossipal 488) A recent study conducted on rubidium levels in freshwater ecosystems from Lake Erie and 2 Arctic lakes indicate that this element biomagnifies (the concentration grows as you move higher in the food chain) in marine food chains. This was found by collecting samples of fish, birds and plankton, and conducting tests on them. They found that the predatory animals (the small-mouth bass, for example) had higher rubidium concentrations than animals commonly considered to be prey. (Campbell et al. 1163)
Caesium (also spelled cesium) is not typically found in any biological systems. However, cesium salt (cesium chloride) is a popular medicinal supplement taken to counteract the effects of damaged or diseased cells on the body. (Ackerman et al. 1011) Furthermore, this supplement has been shown to be toxic to human physiology, and has caused very serious side effects in people, and potentially can be deadly if not taken carefully. (Ackerman et al. 1011)
Francium is an extremely rare element, and its chemical and physical properties are unknown. At any one moment in time, less than one ounce of francium is believed to exist on Earth, and its most stable isotope has a half life of a little less then 23 minutes.("Physics update" 9) It has not been found to exist in any biological systems, and while there is no direct evidence of this, it is assumed to be true due to the rarity and instability of the element.

[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 .

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 .

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 .

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 .

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 .

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 .

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 .

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 .

"Pysics Update." Physics Today June 1996: 9. Academic Search Elite. EBSCO. McIntyre Library, Eau Claire. 9 May 2007 .

"Visual Elements: Group 1 - The Alkali Metals." Visual Elements. Royal Society of Chemistry. .


[edit] See also
Lithium
Sodium
Potassium
Rubidium
Caesium
Francium

[edit] External links
Science aid:Alkali metals A simple look at alkali metals
Doc Brown, Alkali metals
Explanation of above periodic table slice: Alkali metals Atomic numbers in black are solids Solid borders indicate primordial elements (older than the Earth) Dashed borders indicate natural radioactive elements with no isotopes older than the Earth
[show]v • d • ePeriodic tables
Layouts Standard · Vertical · Full names · Names and atomic masses · Text for last · Huge table · Metals and nonmetals · Blocks · Valences · Inline f-block · 218 elements · Electron configurations · Atomic masses · Electronegativities · Alternatives
Lists of elements Name · Atomic symbol · Atomic number · Boiling point · Melting point · Density · Atomic mass
Groups 1 · 2 · 3 · 4 · 5 · 6 · 7 · 8 · 9 · 10 · 11 · 12 · 13 · 14 · 15 · 16 · 17 · 18
Periods: 1 · 2 · 3 · 4 · 5 · 6 · 7 · 8
Series Alkalis · Alkaline earths · Lanthanides · Actinides · Transition metals · Poor metals · Metalloids · Nonmetals · Halogens · Noble gases
Blocks s-block · p-block · d-block · f-block · g-block



[hide] v • d • e Alkali Metals
Lithium
Li
Atomic Number: 3
Atomic Weight: 6.941
Melting Point: 453.69
Boiling Point: 1615
Electronegativity: 0.98
|

Sodium
Na
Atomic Number: 11
Atomic Weight: 22.990
Melting Point: 370.87
Boiling Point: 1156
Electronegativity: 0.96
|

Potassium
K
Atomic Number: 19
Atomic Weight: 39.098
Melting Point: 336.58
Boiling Point: 1032
Electronegativity: 0.82
|

Rubidium
Rb
Atomic Number: 37
Atomic Weight: 85.468
Melting Point: 312.46
Boiling Point: 961
Electronegativity: 0.82
|

Caesium
Cs
Atomic Number: 55
Atomic Weight: 132.905
Melting Point: 301.59
Boiling Point: 944
Electronegativity: 0.79
|

Francium
Fr
Atomic Number: 87
Atomic Weight: (223)
Melting Point: ?295
Boiling Point: ?950
Electronegativity: 0.7



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Categories: Alkali metals | Periodic table