Barium

of these articles is occupied with the chemical element barium. For to identical latin the name of the city Bari see there.
Characteristics
cesium - barium - lanthan
SR
Ba
RA

[Xe] 6s 2
,137
56
Ba

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generally
name, symbol, ordinal number barium, Ba, 56
series of alkaline earth metals
group, period, block 2 (IIA), 2, s
appearance white-grey metallically
proportion at the Earth's shell 0.03%
atomically
atomic mass 137.327
atomic radius (computed) 215 pm (253 pm)
Kovalenter radius 198 pm
van the Waals radius -
Elektronenkonfiguration [Xe] 6 s 2
electrons per energy level 2, 8, 18, 18, 8, 2
1. Ionization energy 502.9 kJ/mol
2. Ionization energy 965.2 kJ/mol
3. Ionization energy 3600 kJ/mol
physically
state of aggregation firmly
crystal structure cubic-body-centered
density (Mohshärte) 3620 kg/m ³ with 20 °C (1,25)
magnetism paramagnetic
melting point 1000 K (727 ° C)
boiling point 1913 K (1640 °C)
molecular volume 38,16 · 10 -6 m 3 /mol
Heat of vaporization 142 kJ/mol
heat of fusion 7.75 kJ/mol
steam pressure 98 Pa with 371 K
speed of sound 1620 m/s
specific thermal capacity 204 j (kg · K)
Electrical conductivity 3 · 10 6 S /m
heat conductivity 18.4 w (m · K)
Chemically
oxidation conditions of 2
oxides (basicity) BaO (basic)
Normalpotenzial -2.912 V (Ba 2+ + 2e - → Ba)
Elektronegativität 0.89 (Pauling scale)
as far as possible and common, are used SI-UNITs.
If not differently notes,
the indicated data apply with standard conditions.

Barium (symbol Ba) is the chemical element with the ordinal number 56. It is an alkaline earth metal and a Periode-6-Element, which were identified to 1774 for the first time by Carl William cross-eyed one. Barium is in the elementary condition metallically - shining and from silvery-white color. It comesbut in nature because of its high reactivity not elementarily forwards. Barium and all soluble compounds are poisonous.

Table of contents

history

barium, already with an easy Oxide coating is covered.

For the first time barium was examined around the year 1600 by the Italian shoemaker and Alchemisten Vincenzo Casciarolo, to which shining Steinchen was noticeable, which shone after heating up in the dark. They became by the publications of Ulisse Aldrovandi onefurther public than „Bologneser stone “admits.1774 identified by the Swedish chemist Carl William cross-eyed one with the investigation this today as barium sulfate admitted of material for the first time barium oxide, which was called first new alkaline earth. Later Johan found two years God dearYawn the same connection when similar investigations. Likewise in 18. Century had been noticeable to the English Mineralogen William Withering in Bleibergwerken Cumberlands a heavy mineral, with that it a lead ore to concern could not and which it the designation„terra pond-pink “gave. It is today well-known as barium carbonate and/or mineralogically as Witherit. Barium, however not in pure form, was made only 1808 by Sir Humphry Davy in England by electrolysis of a mixture of barium oxide and mercury oxide. Thereupon the naming took placeBarium after that before already admitted baryte (of griech. βαρυς: „heavily “, because of its large density).

The first pure representation of the barium took place 1855 via Robert Bunsen and A. Mathiessen by Schmelzelektrolyse of a mixture from barium chloride and ammonium chloride. 1910 from Marie curie under utilization of its similarity was isolated with barium the heavier radium. An important role played the metal also 1938 with the core-chemical experiments Otto of cock and Fritz Strassmanns, the uranium with slow neutrons fired at and toothe much lighter element barium in the reaction products to their astonishment found. The Physikerin Lise Meitner living in the Swedish exile interpreted this unexpected result correctly as result of a nuclear fission.

occurrence

barium comes because of its high reactivity intonature not elementarily, but only in connections forwards. With a portion of approximately 0.03% barium is 14. most frequent element of the earth's crust. Its portion in soils varies between 0,002% and 0,23%, lies on the average howeverwith 0,05%. The barium portion in the Hydrosphäre varies between 10 ppb (billionth portions) in the Atlantic and 20 ppb in the Pacific.

Barium is found particularly in the minerals baryte (or Schwerspat, crystallized barium sulfate) and Witherit (barium carbonate), and usuallyfrom baryte won. The world annual production at baryte rose within the last 30 years of approximately 4.8 million tons (1973) to 6.7 million tons (2003), the world-wide reserves becomes estimated on approximately 400 million tons. The German occurrences of barium connectionsare appropriate in the sour country, in the resin and in Rhineland-Palatinate, the largest occurrence of the world is in Meggen (Westphalia). Occurrences worthy of exploitation of barium connections are however world-wide: the main producing countries of barium are the People's Republic of China, Mexico, India, Turkey, the USA, Germany, Tschechien, Morocco, Ireland, Italy and France.

production and representation

annual are usually won about 4 to 6 million tons barium from barium sulfate. The production from barium carbonate is more simply, however barium carbonate in nature is to be found rarer than barium sulfate. Technically barium from baryte over black ash and barium carbonate is converted into barium oxide, which is then reduced with silicon , aluminum or similar materials to the pure metal. The reaction equationsthis Prozessfolge read:

  • <math> \ mathrm {3 \, BaO \, (s) + 2 \, aluminium \, (s) \ rightarrow Al_2O_3 \, (s) + 3 \, Ba \, (s)}< /math>
  • Barium oxide reacts with aluminum too Alumina and pure barium. This reaction is a variant Thermit process.

Highly pure barium is manufactured by electrolysis of melted barium chloride.

characteristics

chemical and physical characteristics

barium is a firm, paramagnetic alkaline earth metal,in a cubic-body-centered lattice crystallizes. In the chemical characteristics it resembles calcium and the other alkaline earth metals. It reacts more violently than most other alkaline earth metals with water and with oxygen and separates easily in nearly all acids -an exception forms concentrated sulfuric acid, there the education of a sulfate layer (passivation) the reaction stops. Barium can be called therefore one of the unedelsten metals. Because of this high reactivity it is kept under protection liquids (see precautionary measures). It possessesa silver-white color, becomes however fast matte grey at air, because an oxide coating forms (see picture).

oxidiertes Barium
oxidized barium

barium exhibits a green to pale-green flame coloration ; the characteristic spectral lines are with 524,2 and 513,7 Nm.

Barium has a densityfrom 3,62 g/cm 3 (with 20 °C) and ranks thereby among the light alloys. The Mohshärte amounts to 1.25, it is comparatively softly, however harder thereby as the other alkaline earth metals and lead. The melting point is with 1.000 K (727 °C),the boiling point with 1.913 K (1,640 °C). The electro-chemical Standardpotenzial is about -2,912 V.

The keeping of pure barium takes place due to the easy Oxidierbarkeit under Luftabschluss in suitable oxygen-free liquids as for example gasoline. Contrary to other alkaline earth metals formsBarium only a thin oxide coating and can catch fire in damp air.

an atomic mass of 137,327

has characteristics of the isolated barium atom electron configuration

of the barium after the Bohr atom model barium. The atomic radius amounts to 215 pm (computed: 253pm), the Kovalenzradius 198 pm. The Elektronenkonfiguration is [Xe] 6s 2. Barium occurs loaded into ionischen connections doubly. This can be justified with the fact that the sum of the first and second ionization energy is comparatively low, so that thatenergetic expenditure for the splitting off of two electrons by the lattice enthalpy freed with the education of the crystalline solid body to be compensated can.

isotopes and radioactive characteristics

in nature occur seven sturdy barium isotopes , whereby 138 Ba with 71,8%the most frequent isotope is. The moreover one 33 radioactive isotopes with radioactive half-lives are well-known between 10.5 years with 133 Ba and 150 nanoseconds with 153 Ba from barium, whereby most disintegrate however within few seconds. Barium has constantly isotopeswith at least 58 to maximally 97 neutrons (from 114 Ba to 153 Ba). Sturdy barium isotopes result to 137 I in 137 Ba from different decay chains , for example. The radioactive isotopes disintegrate to cesium into lanthans - , xenon - , - and iodine isotopes.In the following table the sturdy four radioactive isotopes are indicated as the longest radioactive half-lives beside the sieved. Further isotopes see Web on the left of.

Isotope n. Frequency atomic weight spin radioactive half-life decay mode CPU MeV decay product Larmorfrequenz
(with 4,8 T)
128 Ba - 127.9083 0+ 2.43 D ε 0.521 128 Cs .
129 Ba - 128,9087 1/2+ 2.23 h ε 2.433 129 Cs .
130 Ba 0.106% 129.90628 0+ stably with 74 neutrons . . . .
131 Ba - 130.9069 1/2+ 11.50 D ε 1.370 131 Cs .
132 Ba 0.101% 131.90505 0+ stably with 76 neutrons . . . .
133 Ba - 132.906 1/2+ 10.51 y ε 0.517 133 Cs .
134 Ba 2.417% 133.90449 0+ stablywith 78 neutrons . . . .
135 Ba 6.592% 134.90567 3/2+ stably with 79 neutrons . . . 19.9 MHz
136 Ba 7.854% 135.90456 0+ stably with 80 neutrons . . . .
137 Ba 11.23% 136,90582 3/2+ stably with 81 neutrons . . . 22.2 MHz
138 Ba 71.7% 137.90524 0+ stably with 82 neutrons . . . .
139 Ba - 138.9088 7/2 83.06 min β 2.317 139 La .
140 Ba - 139,9106 0+ 12.752 D β 1.047 140 La .

Some excerpts from further decay chains in those barium (usually only with radioactive isotopes) is involved:

  • <math> \ mathrm {{} ^ {252} Cf \ longrightarrow {} ^ {142} Ba + {} ^ {106} Mo + 4 {} ^ {1} n}< /math>
Californium disintegrates spontaneously in barium, molybdenum and four neutrons.
  • <math> \ mathrm {{} ^1n + {} ^ {235} U \ longrightarrow {} ^ {145} Ba + {} ^ {88} Kr + 3 {} ^1n}< /math>
Uranium is fired at with slow neutrons and disintegrates thereby into barium, krypton and three further neutrons.
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Use

elementary barium applies only few, for example within special ranges of the metallurgy. It is used occasionally as additive for metal alloys and is a component of many high temperature superconductors, of aluminum and magnesium alloys as getter metal in electron tubes, of vacuum tubes andof nickel barium spark plugs. Regardless of their Giftigkeit also barium connections find multiple application:

proof

wet-chemical methods

a proof reactionis the shifting with diluted sulfuric acid, whereupon white barium sulfate precipitates: <math> \ mathrm {SO_4^ {2 \ operator name {-}} + BaCl_2 \ longrightarrow BaSO_4 \! \ downarrow + 2 \, Cl^ {\ operator name {-}}}< /math> If barium is in society of other elements, which form likewise heavysoluble sulfates, then this procedure cannot be used. Separation andProof take place then, if only alkaline-earth elements are present in the chromate sulfate procedure (see under group of ammonium carbonates). In the context of this procedure the barium solution with potassium chromate solution is shifted and it develops a yellow precipitation of barium chromate. Are still different elements with heavysolubleSulfates available, a suitable cation separation course must be accomplished (see qualitative analysis).

instrumental methods

a procedure suitable for the proof of barium is the atomic spectroscopy. The proof of barium and barium salts is made here by the characteristic spectrum. Common types of device for this are for example the flame atomic absorption spectrometer or the atomic mission spectrometer with inductively coupled high frequency plasma. Even slight traces can be proven by barium. If no spectrometer available is perhaps also simple can one a sample into one Bunsen burner flame hold, and which green flame coloration observe. The application of the flame coloration is not possible, if elements with similar flame colors are present.

toxicology

all water or acid-soluble barium connections are poisonous. The maximum job concentration (MAK value) is with 0,5 mg/m3. A dose from 1 to 15 gram is dependent on the solubility of the respective barium connection for an adult deadly. Into the Röntgenologie used water-insoluble contrast means barium sulfate, that for the representation of the gastro-intestinal tract and/or the sip act in that Video cinematography is used, must be therefore free by soluble barium connections, i.e. when pure substance are supplied. Barium poisonings take place usually on the job or in the proximity of barium-processing branches of industry. Barium can be inhaled or be arrived over the drinking water into the organism.

Is deposited barium in the musculature, which lungs and the bones, to it similarly as calcium, however faster one takes up. Its radioactive half-life in the bone becomes estimated on 50 days. After calcium also at the cell membrane of the musculature by bariumto be replaced can do, - in low dosage - whose permeability one increases and muscle contraction increased which, which can lead to a blood pressure increase and a lowering of the heart frequency, in addition, to muscle cramps. Higher doses lead to myasthenia up to - paralysis, which is attributed to the Beeinträchtung centers of the nervous system. Heartbeat disturbances (Extrasystolie and ventricular fibrillations), Tremor, general weakness feeling, swindles, fear and breath problems can occur. With acute like subacute poisonings disturbances of the gastro-intestinal tract can such as stomach ache, vomiting and Arise to failure. Many symptoms are explained also by the accompanying potassium waste.

First assistance can take place via addition from sodium sulfate - or potassium sulfate solution, whereby the barium ions in heavysoluble and thus innocuous barium sulfate are bound.

connections and reactions

somethe most important reactions of the barium are:

<math> Ba \, (s) + H_2 \, (g) \ rightarrow BaH_2 \, (s) <of /math>
<math> 2 \, Ba \, (s) + O_2 \, (g) \ rightarrow 2 \, BaO \, (s) <of /math>
<math> 3 \, Ba \, (s) + N_2 \, (g) \ rightarrow Ba_3N_2 \, (s) <of /math>
<math> 8 \, Ba \, (s) + S_8 \, (s) \ rightarrow 8 \, BaS \, (s) <of /math>
<math> Ba \, (s) + X_2 \, (s,l, g) \ rightarrow BaX_2 \, (s) <of /math>
<math> Ba \, (s) + 2 \, H_2O \, (l) \ rightarrow Ba^ {2+} \, (aq) + 2 \, OH^ {-} \, (aq) + H_2 \, (g)< /math>
  • with ammonia NH 3 to complexes, which disintegrate to barium amide:
<math> Ba \, (s) + 6 \, NH_3 \, (l) \ rightarrow [Ba (NH_3) _6] </math>
<math> [Ba (NH_3) _6] \ rightarrow Ba (NH_2) _2 + 4 \, NH_3 \, (g) + 3 \, H_2 \, (g)< /math>

Although barium is a light alloy, some barium connections exhibit a high density , as for example with barium sulfate from the mineral name “Schwerspat” to already read off are. Barium connections burn with greener flame. In connectionsbarium always seems to 2+ as Ba .

Important barium connections:

barium in thatanimated nature

plants take up barium from the soil and enrich it. The highest concentration in a useful plant is with a portion of 1% according to 10,000 ppm (millionth portions) with the Paranuss.

Dependent on barium accuratelyagainst it the Zieralgen ( Desmidiaceae) is, a family of single-cell, about a millimeter of large Grünalgen (Chlorophyta), which occur in cold, nutrient-poor sweet waters, in particular in Hochmooren. In their cells are cavities filled with liquid, in which tiny barium sulfate crystals are. To it the necessaryBarium is extracted obviously selectively from the water, even with infinitesimal small concentrations of only 1 ppb (billionth portion). Also around orders of magnitude over it lying concentrations of the lighter alkaline earth metal calcium change in it nothing. Are turned around for other organisms deadly barium concentrations of toto 35 ppm (millionths of portions) tolerates. The biological function of the crystals is still unclear, a role during the weight perception is however assumed. The fact that barium for the plants is essential shows up by the fact that they continue to grow with withdrawal no longer.

Also in the human body barium occurs, the average fabric portion lies with 100 ppb (billionth portions), in blood and bone with in each case up to 70 ppb somewhat lower. With the food daily for instance a Milligramm barium is taken up.

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Literature

  • Harry H. Binder, encyclopedia of the chemical elements. Hirzel, Stuttgart, 1999, ISBN 3-7776-0736-3
  • corner hard Fluck, Klaus G. Hay man, periodic system of the elements, board. Wiley VCH, Weinheim, 2002, ISBN 3-527-30716-8
  • Erwin Riedel, inorganic chemistry. de Gruyter, Berlin, 2002, ISBN 3-11-017439-1
  • A. F. Holleman, Egon Wiberg, text book of inorganic chemistry. de Gruyter, Berlin, 1995, ISBN 3-11-012641-9
  • Morton, W.: Lancet 1956/I, 738, report on a mass poisoning of 84 persons by barium carbonate

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