Mendelevium Mendelevium is a synthetic chemical element; it has symbol Md ( formerly Mv) and atomic number 101. A metallic radioactive transuranium element in the actinide series, it is the first element by atomic number that currently cannot be produced ...

(₁₀₁Md) is a

synthetic element A synthetic element is a known chemical element that does not occur naturally on Earth: it has been created by human manipulation of fundamental particles in a nuclear reactor, a particle accelerator, or the explosion of an atomic bomb; thus, it i ...

, and thus a

standard atomic weight The standard atomic weight of a chemical element (symbol ''A''r°(E) for element "E") is the weighted arithmetic mean of the relative isotopic masses of all isotopes of that element weighted by each isotope's abundance on Earth. For example, ...

cannot be given. Like all artificial elements, it has no

stable isotope Stable nuclides are Isotope, isotopes of a chemical element whose Nucleon, nucleons are in a configuration that does not permit them the surplus energy required to produce a radioactive emission. The Atomic nucleus, nuclei of such isotopes are no ...

s. The first

isotope Isotopes are distinct nuclear species (or ''nuclides'') of the same chemical element. They have the same atomic number (number of protons in their Atomic nucleus, nuclei) and position in the periodic table (and hence belong to the same chemica ...

to be synthesized was ²⁵⁶Md (which was also the first isotope of any element produced one

atom Atoms are the basic particles of the chemical elements. An atom consists of a atomic nucleus, nucleus of protons and generally neutrons, surrounded by an electromagnetically bound swarm of electrons. The chemical elements are distinguished fr ...

at a time) in 1955. There are 17 known

radioisotope A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess numbers of either neutrons or protons, giving it excess nuclear energy, and making it unstable. This excess energy can be used in one of three ...

s, ranging in

atomic mass Atomic mass ( or ) is the mass of a single atom. The atomic mass mostly comes from the combined mass of the protons and neutrons in the nucleus, with minor contributions from the electrons and nuclear binding energy. The atomic mass of atoms, ...

from ²⁴⁴Md to ²⁶⁰Md, and 10

isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, the same number of atoms of each element (chemistry), element – but distinct arrangements of atoms in space. ''Isomerism'' refers to the exi ...

s. The longest-lived isotope is ²⁵⁸Md with a

half-life Half-life is a mathematical and scientific description of exponential or gradual decay. Half-life, half life or halflife may also refer to: Film * Half-Life (film), ''Half-Life'' (film), a 2008 independent film by Jennifer Phang * ''Half Life: ...

of 51.3 days, and the longest-lived isomer is ^258mMd with a half-life of 57 minutes.

List of isotopes

, -id=Mendelevium-244 , rowspan=2, ²⁴⁴Md , rowspan=2 style="text-align:right" , 101 , rowspan=2 style="text-align:right" , 143 , rowspan=2, 244.08116(40)# , rowspan=2,
[] , alpha decay, α , ²⁴⁰Es , rowspan=2, 3+# , - , beta decay, β⁺, spontaneous fission, SF (<14%) , (various) , -id=Mendelevium-244m , style="text-indent:1em" , ^244mMd , colspan="3" style="text-indent:2em" , 200(150)# keV , ~9 μs , IT , ²⁴⁴Md , 7+# , -id=Mendelevium-245 , ²⁴⁵Md , style="text-align:right" , 101 , style="text-align:right" , 144 , 245.08086(28)# , 0.38(10) s , α , ²⁴¹Es , (7/2−) , -id=Mendelevium-245m , style="text-indent:1em" , ^245mMdOrder of ground state and isomer is uncertain. , colspan="3" style="text-indent:2em" , 100(100)# keV , 0.90(25) ms , SF , (various) , 1/2−# , -id=Mendelevium-246 , ²⁴⁶Md , style="text-align:right" , 101 , style="text-align:right" , 145 , 246.08171(28)# , 0.92(18) s , α , ²⁴²Es , 1−# , -id=Mendelevium-246m , rowspan=3 style="text-indent:1em" , ^246mMd , rowspan=3 colspan="3" style="text-indent:2em" , 60(60) keV , rowspan=3, , β⁺ (~67%) , ²⁴⁶Fm , rowspan=3, 4−# , - , α (<23%) , ²⁴²Es , - , β⁺, SF (>10%) , (various) , -id=Mendelevium-247 , rowspan=2, ²⁴⁷Md , rowspan=2 style="text-align:right" , 101 , rowspan=2 style="text-align:right" , 146 , rowspan=2, 247.08152(22)# , rowspan=2, , α (99.14%) , ²⁴³Es , rowspan=2, (7/2−) , - , SF (0.86%) , (various) , -id=Mendelevium-247m , rowspan=2 style="text-indent:1em" , ^247mMd , rowspan=2 colspan="3" style="text-indent:2em" , 153 keV , rowspan=2, , α (80%) , ²⁴³Es , rowspan=2, (1/2−) , - , SF (20%) , (various) , -id=Mendelevium-248 , rowspan=3, ²⁴⁸Md , rowspan=3 style="text-align:right" , 101 , rowspan=3 style="text-align:right" , 147 , rowspan=3, 248.08261(20)# , rowspan=3, , β⁺ (80%) , ²⁴⁸Fm , rowspan=3, , - , α (20%) , ²⁴⁴Es , - , β⁺, SF (<0.05%) , (various) , -id=Mendelevium-249 , rowspan=2, ²⁴⁹Md , rowspan=2 style="text-align:right" , 101 , rowspan=2 style="text-align:right" , 148 , rowspan=2, 249.08286(18) , rowspan=2, , α (75%) , ²⁴⁵Es , rowspan=2, (7/2−) , - , β⁺ (25%) , ²⁴⁹Fm , -id=Mendelevium-249m , style="text-indent:1em" , ^249mMd , colspan="3" style="text-indent:2em" , 100(100)# keV ,
[] , α , ²⁴⁵Es , (1/2−) , -id=Mendelevium-250 , rowspan=3, ²⁵⁰Md , rowspan=3 style="text-align:right" , 101 , rowspan=3 style="text-align:right" , 149 , rowspan=3, 250.084165(98) , rowspan=3, 54(4) s , β⁺ (93.0%) , ²⁵⁰Fm , rowspan=3, 2−# , - , α (7.0%) , ²⁴⁶Es , - , β⁺, SF (0.026%) , (various) , -id=Mendelevium-250m , style="text-indent:1em" , ^250mMd , colspan="3" style="text-indent:2em" , 120(40) keV , 42.4(45) s , α , ²⁴⁶Es , 7+# , -id=Mendelevium-251 , rowspan=2, ²⁵¹Md , rowspan=2 style="text-align:right" , 101 , rowspan=2 style="text-align:right" , 150 , rowspan=2, 251.084774(20) , rowspan=2, , β⁺ (90%) , ²⁵¹Fm , rowspan=2, (7/2−) , - , α (10%) , ²⁴⁷Es , -id=Mendelevium-251m , style="text-indent:1em" , ^251mMd , colspan="3" style="text-indent:2em" , 53(8) keV , 20# s , , , (1/2−) , -id=Mendelevium-252 , ²⁵²Md , style="text-align:right" , 101 , style="text-align:right" , 151 , 252.086385(98) , , β⁺ , ²⁵²Fm , 1+# , - , rowspan=2, ²⁵³Md , rowspan=2 style="text-align:right" , 101 , rowspan=2 style="text-align:right" , 152 , rowspan=2, 253.087143(34)# , rowspan=2,
[] , β⁺ (~99.3%) , ²⁵³Fm , rowspan=2, (7/2−) , - , α (~0.7%) , ²⁴⁹Es , -id=Mendelevium-253m , style="text-indent:1em" , ^253mMd , colspan="3" style="text-indent:2em" , 60(30) keV , 1# min , , , 1/2−# , -id=Mendelevium-254 , ²⁵⁴Md , style="text-align:right" , 101 , style="text-align:right" , 153 , 254.08959(11)# , , β⁺ , ²⁵⁴Fm , 0−# , -id=Mendelevium-254m , style="text-indent:1em" , ^254mMd , colspan="3" style="text-indent:2em" , 50(100)# keV , , β⁺ , ²⁵⁴Fm , 3−# , -id=Mendelevium-255 , rowspan=2, ²⁵⁵Md , rowspan=2 style="text-align:right" , 101 , rowspan=2 style="text-align:right" , 154 , rowspan=2, 255.0910817(60) , rowspan=2, , β⁺ (93%) , ²⁵⁵Fm , rowspan=2, 7/2− , - , α (7%) , ²⁵¹Es , -id=Mendelevium-256 , rowspan=3, ²⁵⁶Md , rowspan=3 style="text-align:right" , 101 , rowspan=3 style="text-align:right" , 155 , rowspan=3, 256.09389(13)# , rowspan=3, , β⁺ (90.8%) , ²⁵⁶Fm , rowspan=3, (1−) , - , α (9.2%) , ²⁵²Es , - , SF (<3%) , (various) , -id=Mendelevium-257 , rowspan=2, ²⁵⁷Md , rowspan=2 style="text-align:right" , 101 , rowspan=2 style="text-align:right" , 156 , rowspan=2, 257.0955373(17) , rowspan=2, , EC (85%) , ²⁵⁷Fm , rowspan=2, (7/2−) , - , α (15%) , ²⁵³Es , -id=Mendelevium-258 , rowspan=3, ²⁵⁸Md , rowspan=3 style="text-align:right" , 101 , rowspan=3 style="text-align:right" , 157 , rowspan=3, 258.0984336(37) , rowspan=3, , α , ²⁵⁴Es , rowspan=3, 8−# , - , β⁻ (<0.0015%) , ²⁵⁸No , - , β⁺ (<0.0015%) , ²⁵⁸Fm , -id=Mendelevium-258m , rowspan=3 style="text-indent:1em" , ^258mMd , rowspan=3 colspan="3" style="text-indent:2em" , 0(200)# keV , rowspan=3, , EC (85%) , ²⁵⁸Fm , rowspan=3, 1−# , - , SF (<15%) , (various) , - , α (<1.2%) , ²⁵⁴Es , -id=Mendelevium-259 , ²⁵⁹MdNot directly synthesized, occurs as decay product of ²⁵⁹No , style="text-align:right" , 101 , style="text-align:right" , 158 , 259.10045(11)# , , SF , (various) , 7/2−# , - , rowspan=4, ²⁶⁰Md , rowspan=4 style="text-align:right" , 101 , rowspan=4 style="text-align:right" , 159 , rowspan=4, 260.10365(34)# , rowspan=4, , SF , (various) , rowspan=4, , - , α (<5%) , ²⁵⁶Es , - , EC (<5%) , ²⁶⁰Fm , - , β⁻ (<3.5%) , ²⁶⁰No

Chronology of isotope discovery

References

* Isotope masses from: ** ** * Half-life, spin, and isomer data selected from the following sources. ** ** ** ** {{Navbox element isotopes Mendelevium