Mendelevium Mendelevium is a synthetic element with the 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 in macrosco ...

(₁₀₁Md) is a

synthetic element A synthetic element is one of 24 known chemical elements that do not occur naturally on Earth: they have been created by human manipulation of fundamental particles in a nuclear reactor, a particle accelerator, or the explosion of an atomic bomb; ...

, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no

stable isotope The term stable isotope has a meaning similar to stable nuclide, but is preferably used when speaking of nuclides of a specific element. Hence, the plural form stable isotopes usually refers to isotopes of the same element. The relative abundanc ...

s. The first

isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numb ...

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

atom Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons. Every solid, liquid, gas, ...

at a time) in 1955. There are 17 known

radioisotope A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess nuclear energy, making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation; transferr ...

s, ranging in

atomic mass The atomic mass (''m''a or ''m'') is the mass of an atom. Although the SI unit of mass is the kilogram (symbol: kg), atomic mass is often expressed in the non-SI unit dalton (symbol: Da) – equivalently, unified atomic mass unit (u). 1&nb ...

from ²⁴⁴Md to ²⁶⁰Md, and 5 isomers. The longest-lived isotope is ²⁵⁸Md with a

half-life Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable at ...

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

List of isotopes

, - , ²⁴⁴Md , style="text-align:right" , 101 , style="text-align:right" , 143 , , , α , ²⁴⁰Es , - , rowspan=2, ²⁴⁵Md , rowspan=2 style="text-align:right" , 101 , rowspan=2 style="text-align:right" , 144 , rowspan=2, 245.08081(33)# , rowspan=2, 0.90(25) ms , SF , (various) , rowspan=2, (1/2−)# , - , α (rare) , ²⁴¹Es , - , rowspan=2 style="text-indent:1em" , ^245mMd , rowspan=2 colspan="3" style="text-indent:2em" , 200(100)# keV , rowspan=2, 400(200) ms
.35(+23−16) s, α , ²⁴¹Es , rowspan=2, (7/2+) , - , β⁺ (rare) , ²⁴⁵Fm , - , rowspan=2, ²⁴⁶Md , rowspan=2 style="text-align:right" , 101 , rowspan=2 style="text-align:right" , 145 , rowspan=2, 246.08171(28)# , rowspan=2, 1.0(4) s , α , ²⁴²Es , rowspan=2, , - , β⁺ (rare) , ²⁴⁶Fm , - , rowspan=2, ²⁴⁷Md , rowspan=2 style="text-align:right" , 101 , rowspan=2 style="text-align:right" , 146 , rowspan=2, 247.08152(22)# , rowspan=2, 1.12(22) s , SF , (various) , rowspan=2, 1/2−# , - , α (rare) , ²⁴³Es , - , rowspan=2 style="text-indent:1em" , ^247mMd , rowspan=2 colspan="3" style="text-indent:2em" , , rowspan=2, ~0.2 s , α (99.99%) , ²⁴³Es , rowspan=2, , - , SF (10⁻⁴%) , (various) , - , rowspan=3, ²⁴⁸Md , rowspan=3 style="text-align:right" , 101 , rowspan=3 style="text-align:right" , 147 , rowspan=3, 248.08282(26)# , rowspan=3, 7(3) s , β⁺ (80%) , ²⁴⁸Fm , rowspan=3, , - , α (20%) , ²⁴⁴Es , - , β⁺, SF (.05%) , (various) , - , rowspan=2, ²⁴⁹Md , rowspan=2 style="text-align:right" , 101 , rowspan=2 style="text-align:right" , 148 , rowspan=2, 249.08291(22)# , rowspan=2, 24(4) s , α (60%) , ²⁴⁵Es , rowspan=2, (7/2−) , - , β⁺ (40%) , ²⁴⁹Fm , - , style="text-indent:1em" , ^249mMd , colspan="3" style="text-indent:2em" , 100(100)# keV , 1.9(9) s , , , (1/2−) , - , rowspan=3, ²⁵⁰Md , rowspan=3 style="text-align:right" , 101 , rowspan=3 style="text-align:right" , 149 , rowspan=3, 250.08442(32)# , rowspan=3, 52(6) s , β⁺ (93%) , ²⁵⁰Fm , rowspan=3, , - , α (7%) , ²⁴⁶Es , - , β⁺, SF (.02%) , (various) , - , rowspan=2, ²⁵¹Md , rowspan=2 style="text-align:right" , 101 , rowspan=2 style="text-align:right" , 150 , rowspan=2, 251.084774(20) , rowspan=2, 4.0(5) min , β⁺ (90%) , ²⁵¹Fm , rowspan=2, 7/2−# , - , α (10%) , ²⁴⁷Es , - , rowspan=2, ²⁵²Md , rowspan=2 style="text-align:right" , 101 , rowspan=2 style="text-align:right" , 151 , rowspan=2, 252.08643(14)# , rowspan=2, 2.3(8) min , β⁺ (50%) , ²⁵²Fm , rowspan=2, , - , α (50%) , ²⁴⁸Es , - , rowspan=2, ²⁵³Md , rowspan=2 style="text-align:right" , 101 , rowspan=2 style="text-align:right" , 152 , rowspan=2, 253.08714(3)# , rowspan=2, 12(8) min
(+12−3) min, β⁺ , ²⁵³Fm , rowspan=2, 7/2−# , - , α , ²⁴⁹Es , - , rowspan=2, ²⁵⁴Md , rowspan=2 style="text-align:right" , 101 , rowspan=2 style="text-align:right" , 153 , rowspan=2, 254.08959(11)# , rowspan=2, 10(3) min , β⁺ , ²⁵⁴Fm , rowspan=2, (0−) , - , α (rare) , ²⁵⁰Es , - , rowspan=2 style="text-indent:1em" , ^254mMd , rowspan=2 colspan="3" style="text-indent:2em" , 50(100)# keV , rowspan=2, 28(8) min , β⁺ , ²⁵⁴Fm , rowspan=2, (3−) , - , α (rare) , ²⁵⁰Es , - , rowspan=3, ²⁵⁵Md , rowspan=3 style="text-align:right" , 101 , rowspan=3 style="text-align:right" , 154 , rowspan=3, 255.091084(7) , rowspan=3, 27(2) min , β⁺ (92%) , ²⁵⁵Fm , rowspan=3, (7/2−) , - , α (8%) , ²⁵¹Es , - , SF (.15%) , (various) , - , rowspan=2, ²⁵⁶Md , rowspan=2 style="text-align:right" , 101 , rowspan=2 style="text-align:right" , 155 , rowspan=2, 256.09389(13)# , rowspan=2, 77(2) min , β⁺ (89%) , ²⁵⁶Fm , rowspan=2, (1−) , - , α (11%) , ²⁵²Es , - , rowspan=3, ²⁵⁷Md , rowspan=3 style="text-align:right" , 101 , rowspan=3 style="text-align:right" , 156 , rowspan=3, 257.0955424(29) , rowspan=3, 5.52(5) h , EC (84.8%) , ²⁵⁷Fm , rowspan=3, (7/2−) , - , α (15.2%) , ²⁵³Es , - , SF (1%) , (various) , - , rowspan=3, ²⁵⁸Md , rowspan=3 style="text-align:right" , 101 , rowspan=3 style="text-align:right" , 157 , rowspan=3, 258.098431(5) , rowspan=3, 51.5(3) d , α (99.99%) , ²⁵⁴Es , rowspan=3, (8−)# , - , β⁻ (.0015%) , ²⁵⁸No , - , β⁺ (.0015%) , ²⁵⁸Fm , - , rowspan=4 style="text-indent:1em" , ^258mMd , rowspan=4 colspan="3" style="text-indent:2em" , 0(200)# keV , rowspan=4, 57.0(9) min , EC (70%) , ²⁵⁸Fm , rowspan=4, 1−# , - , SF (20%) , (various) , - , β⁻ (10%) , ²⁵⁸No , - , α (1.2%) , ²⁵⁴Es , - , rowspan=2, ²⁵⁹MdNot directly synthesized, occurs as decay product of ²⁵⁹No , rowspan=2 style="text-align:right" , 101 , rowspan=2 style="text-align:right" , 158 , rowspan=2, 259.10051(22)# , rowspan=2, 1.60(6) h , SF (98.7%) , (various) , rowspan=2, 7/2−# , - , α (1.3%) , ²⁵⁵Es , - , rowspan=4, ²⁶⁰Md , rowspan=4 style="text-align:right" , 101 , rowspan=4 style="text-align:right" , 159 , rowspan=4, 260.10365(34)# , rowspan=4, 27.8(8) d , SF (85%) , (various) , rowspan=4, , - , α (5%) , ²⁵⁶Es , - , EC (5%) , ²⁶⁰Fm , - , β⁻ (3.5%) , ²⁶⁰No

Chronology of isotope discovery

References

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