332 | The History and Use of Our Earth’s Chemical Elements Hazards
332 | The History and Use of Our Earth’s Chemical Elements Hazards
All the radioisotopes of fermium are dangerous radiation hazards. There is little chance of coming in contact with one of fermium’s isotopes given that they all have very short half-lives and do not exist for long periods. In addition, very small amounts are produced and mainly available for research purposes.
MENDELEVIUM SYMBOL:Md PERIOD:7 SERIESNAME:Actinium ATOMICNO:101
ATOMICMASS:258amu VALENCE:3 OXIDATIONSTATE:+2and+3 NATURALSTATE:Solid ORIGINOFNAME:NamedafterandtohonortheRussianchemistDmitriMendeleevwho developedtheperiodictableofthechemicalelements. ISOTOPES:Thereareatotalof19isotopesofmendelevium.Allofthemareextremely radioactiveandhavehalf-livesrangingfrom900microseconds(forMd-245)to51.5 days(forMd-258).Theyareproducedinverysmallamounts.
ELECTRONCONFIGURATION EnergyLevels/Shells/Electrons Orbitals/Electrons
s2,p6
3-M=18
s2,p6,d10
4-N=32
s2,p6,d10,f14
5-O=31
s2,p6,d10,f13
6-P=8
s2,p6
7-Q=2
s2
Properties Mendelevium’s chemical and physical properties are not well known because such small
amounts with short half-lives have been produced. Many of its isotopes are produced just one atom at a time, making it difficult to weigh and measure samples. Its melting point is thought to be about 1,827°C, but its boiling point and density are unknown.
Characteristics Mendelevium’s most stable isotope is Md-258, with a half-life of 51.5 days. It decays into
einsteinium-254 through alpha (helium nuclei) decay, or it may decay through the process of spontaneous fission to form other isotopes.
AbundanceandSource Only trace amounts of mendelevium have been artificially produced—much of it just one
atom at a time—and thus to date, only several million atoms have been artificially made.
333 Therefore, there is not enough to measure by standard techniques. Other methods, such as
Guide to the Elements |
ion-exchange chromatography and spectroscopy, are employed to study its chemical and physical properties.
History Albert Ghiorso and his team of chemists that included Glenn T. Seaborg, Stanley G.
Thompson, Bernard G. Harvey, and Gregory R. Choppin bombarded atoms of einsteinium- 253 with helium ions in the cyclotron at the University of California at Berkeley. This resulted in a few atoms of mendelevium-256, which is one of the isotopes of mendelevium plus a free neutron.
Before their experiment that produced mendelevium, the team had speculated that this element number 101 must be somewhat similar to the element thulium ( 69 Tm) located just above it in the lanthanide series. Because they did not have a name for this new element, they referred to it as “eka-thulium,” with an atomic number of 101. It was formally named mendelevium in 1955 only after they were able to produce a few atoms of einsteinium by the
nuclear process as follows: 99 Es-253 + 2 H-4 → 101 Md-256 + 0 n-1 (a neutron with a mass of
1 and no charge). (Note: The isotope of einsteinium-258 instead of Es-253 can be used in a similar reaction to produce the more stable isotope mendelevium-258.)
CommonUses Due to the small production and dearth of knowledge about mendelevium, there are no
uses for it beyond basic laboratory research. ExamplesofCompounds
Although little is known about mendelevium, it is possible to form compounds with some nonmetals such as oxygen and the halogen with its +3 ion, as follows:
Mendelevium oxide: 2Md 3+ + 3O 2- → Md 2 O 3 . Mendelevium chloride: Md 3+ + 3Cl 1- → MdCl 3 .
Hazards Similar to all artificially produced radioisotopes that go through natural decay process
or spontaneous fission, mendelevium is an extreme radiation hazard. There is so little of it in existence and produced annually that there is no risk of individual or public radiation poisoning.
NOBELIUM SYMBOL:No PERIOD:7 SERIESNAME:Actinides ATOMICNO:102
ATOMICMASS:259amu VALENCE:3 OXIDATIONSTATE:+2and+3 NATURAL STATE:Solid ORIGINOFNAME:NamedafterthescientistAlfredNobel,whoinventeddynamiteand usedhisfortunetofundandawardtheNobelPrizes. ISOTOPES:Thereatotalof15isotopesofnobelium,rangingfrom0.25milliseconds(No- 250)to58minutes(No-59).Nonearefoundinnature;allareunstableandareartifi- ciallyproducedincyclotrons.
334 | The History and Use of Our Earth’s Chemical Elements
ELECTRONCONFIGURATION EnergyLevels/Shells/Electrons Orbitals/Electrons
s2,p6
3-M=18
s2,p6,d10
4-N=32
s2,p6,d10,f14
5-O=32
s2,p6,d10,f14
6-P=8
s2,p6
7-Q=2
s2
Properties Nobelium is the next to last transuranic element of the actinide series. The transuranic
elements are those of the actinide series that are heavier than uranium. Nobelium is also the heaviest element of the vertical group 16 (VIA).
Because it is only produced in minute quantities and its isotopes have such sort half-lives, not much is known about its properties. It melting point is known and is about 827°C, but its boiling point and density are unknown.
Characteristics Even though nobelium’s chemical and physical properties are unknown, it is reasonable to
assume that they resemble 70 Yb, which is located just above it in the lanthanide series. AbundanceandSource
Nobelium does not exist in nature. All of its isotopes are radioactive with relatively short half-lives. Some are unstable and spontaneously fission, and all of them are artificial and man- made. Small quantities of nobelium are produced in cyclotrons by bombarding curium-246
with carbon-12 and neutrons to produce nobelium-254. The reaction follows: 96 Cm-246 +
6 C-12 → 102 No-254. Carbon’s six neutron and six protons are accelerated to high-speeds in
a cyclotron as they hit the curium atoms with great energy that produces an additional four neutrons, thus producing the net gain in mass number by eight neutrons and an increase in atomic number by six protons, resulting in 102 No-254.
History Three groups had roles in the discovery of nobelium. First, scientists at the Nobel Institute
of Physics in Stockholm, Sweden, used a cyclotron to bombard 96 Cu-244 with heavy carbon
6 C-13 (which is natural carbon-12 with one extra neutron). They reported that they produced an isotope of element 102 that had a half-life of 10 minutes. In 1958 the team at Lawrence Laboratory at Berkeley, which included Albert Ghiorso, Glenn Seaborg, John Walton, and Torbjorn Sikkeland, tried to duplicate this experiment and verify the results of the Nobel Institute but with no success. Instead, they used the Berkeley cyclotron to bombard cerium-
335 246 with carbon-12 to produce nobelium-254 with a half-life of three seconds. (See the
Guide to the Elements |
nuclear process in the previous section titled “Abundance and Source.”) Because the Russian group of scientists in Dubna, Russia, were able to reproduce the results of the Berkeley group, but not the results of the Noble group, the IUPAC, which first awarded credit for the dis- covery of nobelium to the group in Sweden, had to recall it and then award the credit for the discovery of nobelium to the Berkeley group.
CommonUses There are no uses for nobelium except for laboratory research.
ExamplesofCompounds Since nobelium has an oxidation state of +3, its ions are capable of forming compounds
with a few nonmetals, as follows:
Mendelevium fluoride: Md 3+ + 3F 1- → MdF 3 . Mendelevium oxide: 2Md 3+ + 3O 2- → Md 2 O 3 .
Hazards Although nobelium poses a radiation hazard, the chances of being exposed to it are nil since
there is little of it and its isotopes’ half-lives are only a few seconds and minutes. LAWRENCIUM
SYMBOL:Lr PERIOD:7 SERIESNAME:Actinides ATOMICNO:103 ATOMICMASS:262amu VALENCE:3 OXIDATIONSTATE:+3 NATURALSTATE:Solid ORIGINOFNAME:NamedforandinhonorofErnestO.Lawrence,whoinventedthe
cyclotron. ISOTOPES:Thereareatotalof14isotopesoflawrencium.Lawrencium-252hastheshort- esthalf-lifeofjust0.36ofasecond,andlawrencium-262hasthelongesthalf-lifeoffour hours.Nonearefoundinnature.Alltheisotopesoflawrenciumareartificiallymanufac- turedinparticleacceleratorsornuclearreactors.
ELECTRONCONFIGURATION EnergyLevels/Shells/Electrons Orbitals/Electrons
s2,p6
3-M=18
s2,p6,d10
4-N=32
s2,p6,d10,f14
5-O=32
s2,p6,d10,f14
6-P=9
s2,p6,d1
7-Q=2