What exactly is element 43 in the periodic table?

After many years, many people can still remember the mnemonics of the periodic table of chemical elements, but they may only remember those 20 elements. The element we are going to talk about today has an atomic number of 43 and is a radioactive metal element called technetium.

Technetium has a "legendary story"

This element not only had a very difficult discovery process, but it was also the first element in the world to be artificially produced. So, what exactly happened in the process of exploring technetium? Why is this element 43 almost impossible to find on Earth? Next, let's take a look!

The discovery of technetium

As we all know, the arrangement of the periodic table is very particular, and the placement of the radioactive element technetium at position 43 is somewhat out of place, because other radioactive elements are ranked after 80. This is actually closely related to its discovery process.

Schematic diagram of the periodic table of elements

In the 19th century, Mendeleev "predicted" some undiscovered elements in his relevant papers, and mentioned that they were similar to several elements that had already been discovered.

Among them is a manganese-like substance, which is what we call element 43 today.

Mendeleev pointed out that the atomic weight of manganese should be slightly smaller than that of ruthenium, about 100, and it should be able to form salts similar to potassium permanganate.

Russian chemist Mendeleev

In short, since this prophecy came out, more and more scientists have devoted themselves to the search for element 43, and many people thought they had found element 43, but later discovered that it was just a misunderstanding.

In this way, the search for element 43 has repeatedly come to a deadlock, and people even call it the "missing element."

"The Lost Element"

In 1936, when physicist Segel was studying in Berkeley, USA, he found a cyclotron accelerator, some of whose parts showed strong radioactivity after being bombarded by particles. So Segel applied to the manufacturer of the cyclotron accelerator in the hope of obtaining some parts for research.

Later, after receiving the accessory, Shegel discovered that the radioactivity of this component remained for a long time, so he asked Perel, who was good at chemical analysis, to help, and finally separated a small amount of radioactive elements from it.

Schematic diagram of the cyclotron accelerator

It is worth mentioning that after discovering the special features of this element, the two realized that this might be element 43 that everyone had been searching for for decades.

In fact, judging from the discovery process of technetium, this element does seem to be "invisible" in nature, and when it was finally determined to be discovered, it was not naturally produced, but was obtained after molybdenum atoms were bombarded with deuterium.

Conceptual image of molybdenum atom

Therefore, although technetium is a naturally radioactive element in the periodic table, it can basically only be produced artificially and this element is almost impossible to find on the earth.

Why is element 43 so hard to find on Earth?

The elements on Earth are relatively abundant, so after the existence of technetium was confirmed, scientists tried to find technetium that had a longer lifespan or even coexisted with the Earth.

But obviously, the technetium element that was retained at the beginning of the Earth's formation has already decayed over billions of years. Scientists say that in this case, it is impossible for technetium to have been retained from the formation of the Earth's crust to the present.

The Earth is 4.6 billion years old

Of course, the spontaneous fission process of uranium on Earth can continuously generate technetium, and sometimes there is no need for human intervention. Therefore, technetium cannot be called a completely artificial element, and it can still be formed under natural conditions.

Data show that in 1961, 1×10^-9 grams of 99Tc was extracted from 3.5 kg of pitchblende, and 5×10^-10 grams of 99Tc was found in one kilogram of uranium ore. Later, a lot of technetium was also recovered from uranium rods burned in nuclear reactors.

Pitchblende is the main raw material for extracting uranium

In short, although it is indeed difficult to find this guy on Earth, the amount of technetium produced by various reactions is not small, so there is a lot of technetium produced or extracted by other means. It can be seen that element 43 is only missing on the surface, but has actually been with humans all the time.

It is worth mentioning that technetium is rare on Earth but abundant in the universe, especially in thermonuclear reactions on huge stars like the sun, where technetium can be produced.

Schematic diagram of solar thermonuclear fusion

In the 1950s, scientists first discovered the spectral lines of technetium in the spectrum of the sun, and later found the existence of this element in the spectra of many celestial bodies.

After these discoveries, scientists predicted that when a star enters the red giant stage, the technetium element inside it will be enriched to a certain abundance. Due to this characteristic, scientists also call the red giant at this time a "technetium star."

Schematic diagram of the evolution of a sun-like star

Of course, technetium will eventually be thrown into the universe in a brilliant "fireworks" as the life of the star ends. In the process, it will continue to decay, and it will become difficult to find any trace of it.

So, what are the properties of this magical element, technetium? What are its uses?

Technetium: the element that comes and goes without a trace

Properties and uses of technetium

The symbol of technetium is Tc. Its crystal structure is hexagonal close-packed and it looks like a silvery-white metal. When it is kept at low temperatures, technetium can also become a superconductor.

When we observe the properties of isotopes, we can find that their half-lives vary greatly, some are only a few hours, while others are as long as many years.

Technetium is a silvery white metal.

As we said in the previous article, the amount of technetium left on the earth is very small, so in order to obtain this element, in addition to obtaining it from uranium ore that has completed nuclear reactions, people sometimes prepare it artificially in the laboratory.

Since it is a radioactive element, the most basic protection must be taken when preparing technetium. For example, it must be prepared in a ventilated environment. In order to prevent the X-rays emitted by this element from causing damage to human eyes, the experimenters preparing the element must also be equipped with goggles.

You must be fully armed when facing radioactive elements

It is worth mentioning that according to observations, most of the technetium will be excreted after being accidentally inhaled into the body. However, some of it can still be retained in the body through the thyroid gland, so it still has certain harmful components.

Of course, people will not throw the baby out with the bathwater. After all, since technetium has become an artificial chemical element with a production volume measured in kilograms, it means that it actually has its own unique uses in various fields.

Technetium is still very helpful to us

First of all, because the chemical properties of this element are more similar to rhenium, its corrosion resistance is still very strong. A small amount of ammonium technetate can slow down the corrosion rate of steel. And because it is not easy to absorb neutrons, technetium is also widely used in the manufacture of anti-corrosion layers in nuclear reactors.

Secondly, technetium has good superconductivity at low temperatures, so it is often used by scientists as raw material for related experiments.

Nuclear reactor interior

Finally, let’s talk about the contribution of technetium in the medical field. To be more precise, it is the contribution of artificially produced technetium isotopes. As we said before, the half-lives of technetium isotopes vary greatly, and the one widely used in the medical field is technetium-99m, which has a half-life of only about 6 hours. So, what can we do with it?

It turns out that when people take medicine containing technetium-99m, the radiation produced by the decay of this element can be observed by external cameras, thus forming medical images. Of course, when people see the radiation, they may think that this application is still flawed, but it is impossible for radiation to exist in nuclear medicine clinical diagnosis.

Medical imaging after administration of technetium-99m pertechnetate

Most scientists believe that since the gamma rays produced after technetium decay have good performance and a short half-life, they will not cause much harm to the human body after imaging is completed. Therefore, it has always been regarded as one of the best imaging nuclides.

Of course, since the half-life is so short, the shelf life of technetium-99m is also relatively short, so it is generally produced and distributed in a centralized manner.

According to statistics from the 1990s, the use of technetium-99m accounted for more than 80% of the total use of radioactive nuclides for medical diagnosis in the United States.

Technetium-99m Methylene Diphosphonate Injection

In summary, technetium, which is hard to find on Earth and has caused many blunders in the history of exploration, is indeed very useful. And with the continuous advancement of people's preparation technology, technetium has gone beyond the scope of small-scale production and has become one of the artificial elements that can be produced on a large scale. I look forward to this magical element 43 making greater contributions to human society in the future!

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