Fermium (100Fm) is a synthetic element, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no stable isotopes. The first isotope to be discovered (in fallout from nuclear testing) was 255Fm in 1952. 250Fm was independently synthesized shortly after the discovery of 255Fm. There are 20 known radioisotopes ranging in atomic mass from 241Fm to 260Fm (260Fm is unconfirmed), and 2 nuclear isomers, 250mFm and 251mFm. The longest-lived isotope is 257Fm with a half-life of 100.5 days, and the longest-lived isomer is 250mFm with a half-life of 1.8 seconds.
|Main isotopes of fermium (100Fm)|
isotopic mass (u)
|243Fm||100||143||243.07447(23)#||231(9) ms||α (91%)||239Cf||7/2−#|
|244Fm||100||144||244.07404(22)#||3.12(8) ms||SF (99%)||(various)||0+|
|245Fm||100||145||245.07535(21)#||4.2(13) s||α (95.7%)||241Cf||1/2+#|
|246Fm||100||146||246.075350(17)||1.54(4) s||α (85%)||242Cf||0+|
|β+, SF (10%)||(various)|
|247Fm||100||147||247.07695(12)#||31(1) s||α (>50%)||243Cf||(7/2+)|
|248Fm||100||148||248.077186(9)||35.1(8) s||α (93%)||244Cf||0+|
|249Fm||100||149||249.078928(7)||1.6(1) min||β+ (85%)||249Es||(7/2+)#|
|250Fm||100||150||250.079521(9)||30.4(15) min||α (90%)||246Cf||0+|
|250mFm||1199.2(10) keV||1.92(5) s||IT||250Fm||(8−)|
|251Fm||100||151||251.081540(16)||5.30(8) h||β+ (98.2%)||251Es||(9/2−)|
|251mFm||200.09(11) keV||21.1(16) µs||(5/2+)|
|252Fm||100||152||252.082467(6)||25.39(4) h||α (99.99%)||248Cf||0+|
|253Fm||100||153||253.085185(4)||3.00(12) d||EC (88%)||253Es||(1/2)+|
|254Fm||100||154||254.0868544(30)||3.240(2) h||α (99.94%)||250Cf||0+|
|256Fm||100||156||256.091774(8)||157.6(13) min||SF (91.9%)||(various)||0+|
|257Fm[n 2]||100||157||257.095106(7)||100.5(2) d||α (99.79%)||253Cf||(9/2+)|
|260Fm[n 3][n 4]||100||160||260.10281(55)#||4 ms||SF||(various)||0+|
|260Fm?||1992?||254Es+18O, 22Ne — transfer (EC of 260Md)|
260Fm? was not confirmed in 1997.
The actinide or actinoid (IUPAC nomenclature) series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium.Strictly speaking, both actinium and lawrencium have been labeled as group 3 elements, but both elements are often included in any general discussion of the chemistry of the actinide elements. Actinium is the more often omitted of the two, because its placement as a group 3 element is somewhat more common in texts and for semantic reasons: since "actinide" means "like actinium", it has been argued that actinium cannot logically be an actinide, but IUPAC acknowledges its inclusion based on common usage.The actinide series derives its name from the first element in the series, actinium. The informal chemical symbol An is used in general discussions of actinide chemistry to refer to any actinide. All but one of the actinides are f-block elements, with the exception being either actinium or lawrencium. The series mostly corresponds to the filling of the 5f electron shell, although actinium and thorium lack any 5f electrons, and curium and lawrencium have the same number as the preceding element. In comparison with the lanthanides, also mostly f-block elements, the actinides show much more variable valence. They all have very large atomic and ionic radii and exhibit an unusually large range of physical properties. While actinium and the late actinides (from americium onwards) behave similarly to the lanthanides, the elements thorium, protactinium, and uranium are much more similar to transition metals in their chemistry, with neptunium and plutonium occupying an intermediate position.
All actinides are radioactive and release energy upon radioactive decay; naturally occurring uranium and thorium, and synthetically produced plutonium are the most abundant actinides on Earth. These are used in nuclear reactors and nuclear weapons. Uranium and thorium also have diverse current or historical uses, and americium is used in the ionization chambers of most modern smoke detectors.
Of the actinides, primordial thorium and uranium occur naturally in substantial quantities. The radioactive decay of uranium produces transient amounts of actinium and protactinium, and atoms of neptunium and plutonium are occasionally produced from transmutation reactions in uranium ores. The other actinides are purely synthetic elements. Nuclear weapons tests have released at least six actinides heavier than plutonium into the environment; analysis of debris from a 1952 hydrogen bomb explosion showed the presence of americium, curium, berkelium, californium, einsteinium and fermium.In presentations of the periodic table, the lanthanides and the actinides are customarily shown as two additional rows below the main body of the table, with placeholders or else a selected single element of each series (either lanthanum or lutetium, and either actinium or lawrencium, respectively) shown in a single cell of the main table, between barium and hafnium, and radium and rutherfordium, respectively. This convention is entirely a matter of aesthetics and formatting practicality; a rarely used wide-formatted periodic table inserts the lanthanide and actinide series in their proper places, as parts of the table's sixth and seventh rows (periods).Bohrium
Bohrium is a synthetic chemical element with symbol Bh and atomic number 107. It is named after Danish physicist Niels Bohr. As a synthetic element, it can be created in a laboratory but is not found in nature. It is radioactive: its most stable known isotope, 270Bh, has a half-life of approximately 61 seconds, though the unconfirmed 278Bh may have a longer half-life of about 690 seconds.
In the periodic table of the elements, it is a d-block transactinide element. It is a member of the 7th period and belongs to the group 7 elements as the fifth member of the 6d series of transition metals. Chemistry experiments have confirmed that bohrium behaves as the heavier homologue to rhenium in group 7. The chemical properties of bohrium are characterized only partly, but they compare well with the chemistry of the other group 7 elements.Fermium
Fermium is a synthetic element with symbol Fm and atomic number 100. It is an actinide and the heaviest element that can be formed by neutron bombardment of lighter elements, and hence the last element that can be prepared in macroscopic quantities, although pure fermium metal has not yet been prepared. A total of 19 isotopes are known, with 257Fm being the longest-lived with a half-life of 100.5 days.
It was discovered in the debris of the first hydrogen bomb explosion in 1952, and named after Enrico Fermi, one of the pioneers of nuclear physics. Its chemistry is typical for the late actinides, with a preponderance of the +3 oxidation state but also an accessible +2 oxidation state. Owing to the small amounts of produced fermium and all of its isotopes having relatively short half-lives, there are currently no uses for it outside basic scientific research.Georgy Flyorov
Georgy Nikolayevich Flyorov (Russian: Гео́ргий Никола́евич Флёров, IPA: [gʲɪˈorgʲɪj nʲɪkɐˈlajɪvʲɪtɕ ˈflʲɵrəf]; 2 March 1913 – 19 November 1990) was a Soviet nuclear physicist who is known for his discovery of spontaneous fission and his contribution towards the physics of thermal reactions. In addition, he is also known for his letter directed to Joseph Stalin, during the midst of World War II, to start the atomic bomb project in the Soviet Union.
In 2012, element 114 was named flerovium after the research laboratory at the Joint Institute for Nuclear Research bearing his name.Mendelevium
Mendelevium is a synthetic element with chemical symbol Md (formerly Mv) and atomic number 101. A metallic radioactive transuranic element in the actinide series, it is the first element that currently cannot be produced in macroscopic quantities through neutron bombardment of lighter elements. It is the third-to-last actinide and the ninth transuranic element. It can only be produced in particle accelerators by bombarding lighter elements with charged particles. A total of sixteen mendelevium isotopes are known, the most stable being 258Md with a half-life of 51 days; nevertheless, the shorter-lived 256Md (half-life 1.17 hours) is most commonly used in chemistry because it can be produced on a larger scale.
Mendelevium was discovered by bombarding einsteinium with alpha particles in 1955, the same method still used to produce it today. It was named after Dmitri Mendeleev, father of the periodic table of the chemical elements. Using available microgram quantities of the isotope einsteinium-253, over a million mendelevium atoms may be produced each hour. The chemistry of mendelevium is typical for the late actinides, with a preponderance of the +3 oxidation state but also an accessible +2 oxidation state. Owing to the small amounts of produced mendelevium and all of its isotopes having relatively short half-lives, there are currently no uses for it outside basic scientific research.