Technetium is the lightest metal which has no stable isotopes. It's the first element to have been produced artificially, and its name means "artificial", and this is all curious as it's otherwise in an unremarkable section of the periodic table. To the left is molybdenum, present in various plant enzymes; to the right is ruthenium, often used in electrical contacts. Yet my chemistry textbook doesn't even assign technetium a relative atomic mass - none of its isotopes are particularly that abundant, with the next element to have this dubious honour being polonium.
Technetium is in the same group as manganese, and when Dmitry Mendeleev was first making his periodic table, he called what would later be technetium "eka-manganese", since it was one below manganese. After the first table was made, many scientists claimed to have discovered technetium, though it took until the 1920s for it to first be synthesised.
The most stable technetium isotopes are:
- 97Tc, which has a half life of over 2,500,000 years (for comparison, 235U has a half life of over 700,000,000 years)
- 98Tc, with a half life of over 4,000,000 years.
- 99Tc, with a half life of about 210,000 years
However, there are various other isotopes, with half lives ranging from several days (96Tc) to a few milliseconds (120Tc). This website covers various isotopes, with technetium's in row 43, and one thing you'll notice is that, whilst the most stable isotopes are all in a diagonal blue band, technetium's is particularly small compared to molybdenum and ruthenium.
Technetium does shine in medicine, though, with the isotope 99mTc. This is a metastable isotope which comes from the decay of 99Mo, and it has a half life of about six hours. Since it undergoes gamma decay, 99mTc is thus a good, non-ionising medical tracer, used for diagnostic imagery of various organs, such as kidneys and lungs. The same goes for sodium pertechnetate, which contains the 99mTcO4- ion which has similar properties to an I- ion; iodine plays a key role in the functioning of the thyroid gland. Both can be used in scans used for thyroid gland treatment.
Technetium has also been found in the spectral lines of stars, which sparked the field of nucleosynthesis - the process of creating new elements from old ones. Since technetium is unstable, this discovery surprised many, and led to the theory that technetium must have been created during stellar evolution, specifically during star death. It appears unlikely that there could be a stable technetium isotope that meant it could be present in the stars, since it can survive helium flashes, and other high temperature events, without significant decay, so any present technetium must have been recent enough. Therefore, technetium must have been created through endless neutron collisions that occurred due to star death. This article is a comprehensive read into technetium's role in star death, if you're curious.
Perhaps through its oddness, technetium is a remarkably useful and curious element, artificial as it may seem.
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