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 macroscopi ...
(
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 numbers) ...
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, and ...
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&nbs ...
from
244Md to
260Md, and 5
isomer
In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers.
Iso ...
s. 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 ato ...
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,
259Md
[Not 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
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 macroscopi ...