Francium is a kind ofradioactive element, chemical symbol is Fr, atomic number is 87Alpha decayThe product exists in a very small amount in nature.It is radioactive, and Fr-223 isBeta radiator，half lifeAbout 21 minutes.KnownisotopeThere are 21 kinds of unstable radioactive elements with very short half-life.Fr-223 has the longest life.The three isotopes with longer lifetime behind it are Fr-212, Fr-222 and Fr-221, and their half-life is 19.3 minutes, 14.8 minutes and 4.8 minutes respectively.
Francium has a very short life, so it is difficult to study its chemical properties carefully.But it belongs toalkali metal, in some ways andcesiumAre similar in nature.FranciumMetallicityOn the contrary, it is not as good as cesium,Metal mobilityIs weaker thanpotassiumandbarium。
Chinese name
Francium
Foreign name
Francium
Alias
Caesium like、鍅
CAS login number
7440-73-5
Melting point
27 ℃
Boiling point
677 ℃
Water solubility
React with water
Density
1.87 g/cm³
Appearance
Silver white soft metal
Atomic number
eighty-seven
Element Category
metallic element
Element symbol
Fr
Cycle
Seventh cycle
area
S area
Atomic weight
two hundred and twenty-three point zero one nine seven
Francium is a cesium like substance pointed out by MendeleevMoseley The determined atomic number is 87.Its discovery has gone through a winding road.
At the beginning, chemists inferred from Mendeleev that cesium like is aAlkali metal elementIt is a salt forming element. I tried to find it from various salts, but I got nothing.
In July 1925, the British chemist Friendre specially chose the hot summer to look for it in the Dead Sea.However, after chemical analysis and spectral analysis, this element was not found.
Later, many chemists tried to use spectral technology and atomic weight as a breakthrough to find this element, but they failed.
In 1930, Alison, a professor of physics at the Alabama Institute of Technology, announced the discovery of element 87 in rare alkali minerals cesium pyroxene and lepidolite by magneto-optical analysis.The element symbol is set as Vi.However, before long, the magneto-optical analysis itself was denied, and the elements discovered by using it could not be established.
By 1939, Perry, a French female scientist, was studying theαDecay products.Element 87 was found and studied.In memory of her motherland, element 87 is called francium, and the element symbol is Fr.
Physical and chemical properties
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Atomic attribute
Relative atomic mass: 223.0197
Atomic radius: 0.27nm
Valence electron arrangement: 7sone
Valence electrons are arranged in each energy level: 2, 8, 18, 32, 18, 8, 1
Electronic number: 2-8-18-32-18-8
Electronic layer: K-L-M-N-O-P
Oxidized state: mainly+1
Crystal structure: body centered cubic cell, each cell contains 2 metal atoms
physical property
Material state: solid, radioactive
Melting point: 300.2K (27 ℃)
Boiling point: 950K (677 ℃)
chemical property
Due to nuclear instability, the maximum half-life of Fr-223 is only 21 minutes.Its chemical properties can only be studied in the trace range.It is the heaviest alkali metal element and is also extremely unstable like other alkali metals.Francium is chemically active, and all francium salts are water-soluble.Because it is radioactive and its chemical reaction is extremely active, there is no way to obtain pure francium.[2]
application area
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Because of its instability and rarity, francium has not yet been commercially used.It has been used in the research field of biology and atomic structure.Francium's help in the diagnosis of cancer has also been studied in depth, but it is not considered practical.
Francium can be found in uranium ore and thorium ore, every 1 × 10eighteenOnly one francium atom can be found out of every uranium atom.It can also be obtained by bombarding thorium with protons.Or through the following nuclear reactions:one hundred and ninety-sevenAu+eighteenO→two hundred and tenFr+5n
resource distribution
It is estimated that since the half-life of francium is very short, the content of francium in the crust at any time is about 30g after calculation.This makes it the second rarest element besides astatine.Even among the ores with the highest content, there are only 0.0000000000037 grams per ton.
isotope
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All isotopes of francium with mass 199-232 have been found, of which only francium-223 and 224 are natural radioisotopes. Among them, francium-223 has the longest half-life, about 22 minutes.The rest are synthesized by artificial nuclear reaction.[3]
world record
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The most unstable natural element in the world：Francium, discovered by Maguerite Perey of the Curie Institute in Paris, France, in 1939, is the most unstable naturally occurring element in the periodic table. Its most stable isotope Francium-223 has a half-life of only 22 minutes.(Guinness World Records)
