Technetium

Technetium is a chemical element with the symbol Tc and atomic number 43. It is special because all of its forms are radioactive, making it the lightest element that does not occur naturally in a stable state. Unlike most elements, technetium does not exist in nature in large amounts. Instead, it is made by humans in laboratories and factories.

This element was first created in 1937, and its name comes from the Greek word for "artificial." Technetium sits between manganese and rhenium on the periodic table, and its properties are a mix of these two neighbors.

One of the most useful forms of technetium is called technetium-99m. It gives off a type of energy called gamma rays for a short time and is used in hospitals to help doctors see inside the body. This helps in diagnosing illnesses, such as problems with bones. Another form, technetium-99, is used in scientific studies because it gives off beta particles without gamma rays. Technetium is also found in stars, and its presence helped scientists understand how stars create heavier elements.

History

Early assumptions

In the 1860s to 1871, early versions of the periodic table made by Dmitri Mendeleev had a space between molybdenum (element 42) and ruthenium (element 44). In 1871, Mendeleev said this missing element would fit below manganese and act like it. He called it eka-manganese because eka means "one" in Sanskrit.

Early misidentifications

Many scientists wanted to find this missing element. But it was hard to find because technetium is radioactive.

Irreproducible results

Official discovery and later history

In 1937, Carlo Perrier and Emilio Segrè proved element 43 existed. In 1936, Segrè got some radioactive parts from a cyclotron in the United States. He and Perrier used them to show the element was real. In 1947, they named it technetium after the Greek word for "artificial" because it was made in a lab.

Later, scientists found technetium in stars. This showed that heavier elements are made inside stars. Technetium is also found in very tiny amounts in some Earth materials.

Characteristics

Technetium is a silvery-gray radioactive metal that looks like platinum. It is usually found as a gray powder.

Technetium is found in group 7 of the periodic table, between rhenium and manganese. Its chemical behavior is similar to rhenium, especially in how it does not react easily and forms certain types of bonds. Unlike manganese, technetium does not easily form ions with a positive charge. It can exist in nine different oxidation states, with +4, +5, and +7 being the most common. Technetium dissolves in special liquids called aqua regia, nitric acid, and concentrated sulfuric acid, but not in hydrochloric acid.

Metallic technetium can change color slightly in moist air, and when in powder form, it can catch fire in oxygen. It can also react with hydrogen and carbon under certain conditions.

Compounds

Pertechnetate and other derivatives

Main article: Pertechnetate

The most common form of technetium that we can easily get is called sodium pertechnetate. It is made when a certain material breaks down during a process called radioactive decay.

Pertechnetate behaves in a special way when mixed with water and acts like another chemical called perchlorate. It is not very strong at taking away electrons from other materials.

Another form of technetium is technetium heptoxide. This is a pale-yellow solid that is made when technetium metal mixes with oxygen. It changes back into pertechnetate and another chemical when added to water.

Other chalcogenide derivatives

Technetium can mix with other elements to form different compounds. For example, it can form dioxide, disulfide, and similar materials. These compounds change when heated or mixed with other chemicals.

Unlike a similar element called rhenium, technetium does not form a certain type of compound called a trioxide, although scientists have found signs of it in tests.

Simple hydride and halide complexes

Technetium can also form compounds with hydrogen and halogens like fluorine and chlorine. These compounds have different structures depending on how they are made and can change when heated.

Technetium forms many different compounds with halogens. These compounds can have various structures, like chains or clusters of atoms.

There are two different forms of a technetium chloride compound. One form has a special structure with triangles of atoms, while the other has pairs of atoms arranged in a certain way. Similar structures exist for compounds with bromine and iodine.

Several technetium compounds with halogens can change into forms with six halogens around each technetium atom. Even more reduced forms create clusters of technetium atoms bonded together.

Coordination and organometallic complexes

Technetium can form many compounds with organic materials. These are important in medical imaging.

Technetium also forms compounds where it bonds directly to carbon atoms. One example is a compound with carbon monoxide, where two technetium atoms are connected and each is surrounded by five carbon monoxide molecules. These compounds are useful in medical studies.

Isotopes

Main article: Isotopes of technetium

Technetium, with atomic number Z = 43, is the lightest element in the periodic table where all its forms are unstable and change over time. Another element like this is promethium, which has atomic number 61. Elements with an odd number of tiny parts called protons tend to be less stable.

The forms of technetium that stay around the longest are technetium-97 and technetium-98, each lasting about 4.2 million years. Another form, technetium-99, lasts for around 211,100 years. There are thirty-four other forms of technetium that scientists have studied, with most lasting less than an hour. A few last a bit longer, like technetium-93, which stays for about 2.75 hours.

When these forms change, lighter ones usually turn into molybdenum, while heavier ones turn into ruthenium. Technetium also has special forms called nuclear isomers, where some parts are extra excited. The most stable of these is technetium-97m, lasting 91.1 days.

Technetium-99 is found when uranium-235 splits apart, making it the most common form of technetium that we can find. One gram of technetium-99 changes very quickly.

Occurrence and production

Technetium is very rare in nature, found in tiny amounts in the Earth's crust. It mostly exists because of processes in stars and as a byproduct in nuclear reactors.

When uranium undergoes nuclear fission in reactors, it produces technetium-99. This isotope is a major part of radioactive waste and can be released into the environment during nuclear tests or from nuclear facilities.

Technetium-99m, a form used in medicine, is made by irradiating uranium targets in reactors. Most of this supply comes from a few reactors, but as these age, finding new sources becomes important. Scientists also look at other ways to create technetium, like using particle accelerators.

Applications

Nuclear medicine and biology

Technetium-99m is a special form of the element technetium that doctors use in medical tests. It helps doctors see inside the body without surgery. This is because it gives off a type of energy that special machines can detect. It also disappears quickly, which makes it safe for these tests. Doctors can attach it to different substances so it can travel to different parts of the body, like the brain, heart, or bones, to help find problems.

There is another form of technetium, called technetium-95m, that lasts longer. Scientists use it to study how technetium moves through the environment and living things.

Industrial and chemical

Technetium-99 can be used to check and fix scientific equipment because it gives off a steady, low level of energy. It can also be used in tiny power sources and in helping certain chemical reactions happen. However, its radioactivity makes it tricky to use in everyday applications.

Adding a tiny amount of a technetium compound to water can help protect steel from rusting, even at high temperatures. This works by forming a thin protective layer on the steel. But because technetium is radioactive, this use is limited to special, closed systems.

Precautions and biological effect

Technetium does not play a role in the human body and is not normally found there. It is made in large amounts by splitting atoms in nuclear reactions and can spread more easily than many other radioactive materials. It seems to have low harm to chemicals in the body. For example, tests with rats showed no big changes when they ate up to 15 micrograms of technetium-99 per gram of food for several weeks. In the body, technetium changes quickly into a stable form that dissolves well in water and is passed out of the body fast.

All forms of technetium need careful handling. The most common form, technetium-99, gives off a weak type of radiation that can be stopped by glass. The biggest danger when working with technetium is breathing in dust, which can harm the lungs and increase cancer risk. For most work, using a special air-flow table is enough, and a sealed box is not usually needed. Technetium does not rust easily and can clean itself when organisms try to stick to it because of its radiation.