Actinide element

15 chemical elements with atomic numbers from 89 to 103

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Actinides are cycle It is the general name of 15 chemical elements with atomic numbers of 89~103 in the Ⅲ B group. They include actinium, thorium, protactinium, uranium, neptunium, plutonium, americium, curium, berkelium, californium, einsteinium, manganese, nanometer and lawrencium, all of which are radioactive element 。 The element with atomic number greater than 92 after uranium in the periodic table is called Transuranic element^[2] 。 Top 6 actinides element Actinium 、 thorium 、 Protactinium 、 uranium 、 Neptunium 、 plutonium It exists in nature, and the other nine are all artificial nuclear reaction synthesis.

Chinese name: Actinide element
Foreign name: Actinicles

Alias: 5f transition system
Represent: An

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seven chemical property
eight Nuclear property

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Actinide element

Actinides

In periodic system Ⅲ B family atom The general name of 15 chemical elements with the order of 89~103.

definition

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Actinides, also known as 5f transition system, are periodic table of ele ments 15 chemical elements with atomic numbers of 89~103 in Group IIIB. they chemical property Similar, so they form a series separately, occupying a special place in the periodic table of elements. It is represented by the symbol An.

brief introduction

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Actinides include actinium (Ac), thorium (Th), protactinium (Pa), uranium (U), neptunium (Np) plutonium (Pu), americium (Am), curium (Cm), berkelium (Bk), californium (Cf), einsteinium (Es), febrium (Fm), extra element (Md), nanometer (No), lawrencium (Lr) are all radioactive elements. The element with atomic number greater than 92 after uranium in the periodic table is called transuranium element. The first 6 actinides, thorium, protactinium, uranium, neptunium and plutonium exist in nature, and the other 9 actinides are all synthesized by artificial nuclear reaction. Of the synthetic actinides, only plutonium, neptunium, americium and curium have an annual output of more than kg, and californium is only gram. Since the amount of heavy actinides after einsteinium is extremely small, half life Very short, only used for research and identification under laboratory conditions nuclide nature. In 1789, M.H. Klaproth (1743-1817) from Pitchblende Uranium, the first actinide element known by people, was discovered in. Later, actinium, thorium and protactinium were successively discovered. Post uranium element They were all synthesized by artificial nuclear reaction after 1940, called synthetic elements. Since actinides are all metals, they can Lanthanide Collectively referred to as zone f metals.

nature

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Actinides are all metals. Like lanthanides, actinides are chemically active. Their chloride 、 sulfate 、 Nitrate 、 Perchlorate Soluble in water, hydroxide 、 fluoride 、 sulfate 、 oxalate Insoluble in water. Most actinides can form Coordination compound 。 Alpha decay And spontaneous fission are important nuclear characteristics of actinides Atomic number The half-life of uranium 238 decreases with the increase of half life 4.468 billion years; The half-life of lawrencium 260 is only 3 minutes. Toxicity and radiation of actinides (especially those inhaled into human body Alpha radiator ）Because of its great harm, these substances must be operated in a closed work box with protective measures.

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Among the synthetic actinides, only plutonium, neptunium, americium and curium have an annual output of more than kilogram, californium is only gram, and the amount of elements after einsteinium is very small, with a very short half-life, which is only used for research. Those with more uses are limited to uranium and thorium, and plutonium is used in some cases nuclear fuel 。

element name	Chemistry Symbol	Atomic weight	Electronic configuration 5f 6d 7s	Oxidized state
Actinium	Ac	two hundred and twenty-seven point zero two seven eight	1 2	+3
thorium	Th	two hundred and thirty-two point zero three eight one	2 2	+2,+3,+4
Protactinium	Pa	two hundred and thirty-one point zero three five nine	2 1 2	+2,+3, +4,+5
uranium	U	two hundred and thirty-eight point zero two eight nine	3 1 2	+2,+3, +4,+5,+6
Neptunium	Np	two hundred and thirty-seven point zero four eight two	4 1 2	+3,+4,+5 +6,+7
plutonium	Pu	(244)^[3]	6 2	+3,+4 +5,+6,+7
Americium	Am	(243)	7 2	+2,+3 +4,+5,+6
Curium	Cm	(247)	7 1 2	+3,+4
Berkeleton	Bk	(247)	9 2	+3,+4
Californium	Cf	(251)	10 2	+2,+3,+4
Einsteinium	Es	(252)	11 2	+2,+3
Of	Fm	(257)	12 2	+2,+3
Extra	Md	(258)	13 2	+1,+2,+3
Nanometer	No	(259)	14 2	+2,+3
Lawrencium	Lr	(260)	14 1 2	+3

Electronic configuration

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Lanthanides and actinides

The electronic configuration of the ground state of actinides is 5f 0~14 6d 0~1 7s two The extranuclear electrons of these elements are divided into 7 layers, the outermost layer is 2 electrons, and the secondary outer layer is mostly 8 electrons (9 or 10 electrons in some cases). The fifth layer is filled with electrons from protactinium to nano meter, increasing the number of electrons in the fifth layer from 18 to 32. according to Nucleus Extraneous Electronic energy level In the seventh cycle of the periodic table, elements after actinium fill 5f inner electrons successively until 14 5f inner electrons are filled. Since the outermost electron configuration of atoms is basically the same, and only the inner layer of 5f alternates electrons, these elements form their own series of actinides. The actinide theory based on this assumption was developed by G T. Siberg put forward in 1944. According to this theory, the last element of actinide series is element 103, while element 103 element 104 It is expected that it does not belong to actinide series but belongs to the fourth sub group. The successful synthesis of transuranic elements and the study of their chemical properties, especially the discovery of element 104, have confirmed that Actinide theory Is correct. The atomic structure of actinides is characterized by that the electrons of the elements after actinides fill the 5f inner electron layer in turn. Their outermost electronic configurations are basically the same, making the properties of actinides very similar. Like lanthanides, actinides also have the phenomenon of ion radius contraction.

chemical property

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Since the elements of the lanthanide and actinide series only fill electrons in the inner orbital (corresponding 4f and 5f orbitals) with the increase of atomic number, the outer orbital (corresponding 6s, 5d and 7s, 6d orbitals) Electronic layout Basically the same, so not only the chemical properties of lanthanides and actinides are similar, but also the chemical properties of elements in each series are similar.

Most actinides have the following properties:

Can form Complex ion Trivalent cation with the organic chelate; Produce trivalent insoluble compounds, such as hydroxide, fluoride, carbonate and oxalate Etc; Produce trivalent soluble compounds, such as sulfate, nitrate, perchlorate and some halides. stay aqueous solution Most actinides in the are in the+3 oxidation state, and the first and last actinides have different oxidation states, for example, protactinium has the+5 oxidation state; Uranium, neptunium and americium have+5 and+6 oxidation states, and neptunium and plutonium have+7 oxidation states (the highest oxidation state in lanthanides is+4); Elements such as californium, einsteinium, rare earth, rare earth and nanometer all have+2 oxidation state. The difference between actinides and lanthanides is that the energy required for 5f electrons in light actinides to be excited to the 6d orbit is less than the energy required for 4f electrons in corresponding lanthanides to be excited to the 5d orbit, which makes actinides have more bonding electrons than lanthanides, so higher Oxidized state ； The heavy actinides are just the opposite.

The phenomenon of ion radius contraction is found in actinides and lanthanides, that is, the ion radius decreases with the increase of atomic number. In actinide elements, when filling the first few 5f electrons, the ion radius shrinks significantly, and then tends to flatten, making the ion radius of these elements very close. Therefore, the difference in chemical properties of actinides gradually decreases with the increase of atomic number, so that it is more and more difficult to separate actinides (especially heavy actinides) one by one. Solvent extraction and ion exchange are widely used separation methods, especially in the discovery of elements such as berberium, californium, einsteinium, Ion exchange chromatography It has played an important role. be based on Ionic radius The minor difference of Complexation , actinides can be classified from Ion exchange column Rinse it down.

Nuclear property

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Alpha decay And spontaneous fission are important nuclear characteristics of actinides. With the increase of atomic number, the half-life decreases in turn. In the element half life For the longest isotope, the half-life of uranium 238 is 4.468 × 10 nine The half-life of californium 251 is 898 years, and that of lawrencium 260 is only 3 minutes.

Actinides have high toxicity and radiation hazards (especially alpha radiators inhaled into the body), so they must be operated in a closed work box with protective measures.^[1]

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