Periodic Table > Technetium


Some elements exist in several different structural forms, these are called allotropes.

For more information on Murray Robertson’s image see Uses and properties facts below.


Fact box terminology

Elements appear in columns or ‘groups’ in the periodic table. Members of a group typically have similar properties and electron configurations in their outer shell.

Elements are laid out into rows or ‘periods’ so that similar chemical behaviour is observed in columns.

Elements are organised into blocks by the orbital type in which the outer electrons are found. These blocks are named for the characteristic spectra they produce: sharp, principal, diffuse, and fundamental.

Atomic Number
The number of protons in the nucleus.

Atomic Radius/non -bonded (Å)
based on Van der Waals forces (where several isotopes exist, a value is presented for the most prevalent isotope). These values were calculated using a multitude of methods including crystallographic data, gas kinetic collision cross sections, critical densities, liquid state properties, for more details please refer to the CRC Handbook of Chemistry and Physics.

Electron Configuration
The arrangements of electrons above the last (closed shell) noble gas.

Elements are defined by the number of protons in its centre (nucleus), whilst the number of neutrons present can vary. The variations in the number of neutrons will create elements of different mass which are known as isotopes.

Melting Point (oC)
The temperature at which the solid-liquid phase change occurs.

Melting Point (K)
The temperature at which the solid-liquid phase change occurs.

Melting Point (oF)
The temperature at which the solid-liquid phase change occurs.

Boiling Point (oC)
The temperature at which the liquid-gas phase change occurs.

Boiling Point (K)
The temperature at which the liquid-gas phase change occurs.

Boiling Point (oF)
The temperature at which the liquid-gas phase change occurs.

Elements that do not possess a liquid phase at atmospheric pressure (1 atm) are described as going through a sublimation process.

Density (g cm-3)
Density is the mass of a substance that would fill 1 cm3 at room temperature.

Relative Atomic Mass
The mass of an atom relative to that of Carbon-12. This is approximately the sum of the number of protons and neutrons in the nucleus. Where more than one isotope exists the value given is the abundance weighted average.

Key Isotopes (% abundance)
An element must by definition have a fixed number of protons in its nucleus, and as such has a fixed atomic number, however variants of an element can exist with differing numbers of neutrons, and hence a different atomic masses (e.g. 12C has 6 protons and 6 neutrons and 13C has 6 protons and 7 neutrons).

CAS number
The Chemical Abstracts Service registry number is a unique identifier of a particular chemical, designed to prevent confusion arising from different languages and naming systems (where several isotopes exist, a value is presented for the most prevalent isotope).

Fact box

Group Melting point 2157 oC, 3915 oF, 2430 K 
Period Boiling point 4262 oC, 7704 oF, 4535 K 
Block Density (g cm-3) 11 
Atomic number 43  Relative atomic mass [98]  
State at 20°C Solid  Key isotopes Unknown 
Electron configuration [Kr] 4d55s2  CAS number 7440-26-8 
ChemSpider ID 22396 ChemSpider is a free chemical structure database

Uses and properties terminology

Image Explanation

Murray Robertson is the artist behind the images which make up Visual Elements. This is where the artist explains his interpretation of the element and the science behind the picture.

Natural Abundance

Where this element is most commonly found in nature.

Biological Roles

The elements role within the body of humans, animals and plants. Also functionality in medical advancements both today and years ago.


The description of the element in its natural form.

Uses and properties

Image explanation
The symbol of a human hand reflects the fact that the element is created artificially, and its name means ‘artificial’.
A radioactive, silvery metal that does not occur naturally.
The gamma-ray emitting technetium-99m (metastable) is widely used for medical diagnostic studies. Several chemical forms are used to image different parts of the body.

Technetium is a remarkable corrosion inhibitor for steel, and adding very small amounts can provide excellent protection. This use is limited to closed systems as technetium is radioactive.
Biological role
Technetium has no known biological role. It is toxic due to its radioactivity.
Natural abundance
The metal is produced in tonne quantities from the fission products of uranium nuclear fuel. It is obtained as a grey powder.

Early chemists puzzled over why they could not discover element number 43, but now we know why – its isotopes are relatively short-lived compared to the age of the Earth, so any technetium present when the Earth formed has long since decayed.
Atomic data terminology

Atomic radius/non -bonded (Å)
Based on Van der Waals forces (where several isotopes exist, a value is presented for the most prevalent isotope). These values were calculated using a multitude of methods including crystallographic data, gas kinetic collision cross sections, critical densities, liquid state properties,for more details please refer to the CRC Handbook of Chemistry and Physics.

Electron affinity (kJ mol-1)
The energy released when an additional electron is attached to the neutral atom and a negative ion is formed (where several isotopes exist, a value is presented for the most prevalent isotope). *

Electronegativity (Pauling scale)
The degree to which an atom attracts electrons towards itself, expressed on a relative scale as a function bond dissociation energies, Ed in eV. χA - χB =(eV)-1/2sqrt(Ed(AB)-[Ed(AA)+Ed(BB)]/2), with χH set as 2.2 (where several isotopes exist, a value is presented for the most prevalent isotope).

1st Ionisation energy (kJ mol-1)
The minimum energy required to remove an electron from a neutral atom in its ground state (where several isotopes exist, a value is presented for the most prevalent isotope).

Covalent radius (Å)
The size of the atom within a covalent bond, given for typical oxidation number and coordination (where several isotopes exist, a value is presented for the most prevalent isotope). ***

Atomic data

Atomic radius, non-bonded (Å) 2.16 Covalent radius (Å) 1.38
Electron affinity (kJ mol-1) 53.07 Electronegativity
(Pauling scale)
Ionisation energies
(kJ mol-1)

Mining/Sourcing Information

Data for this section of the data page has been provided by the British Geological Survey. To review the full report please click here or please look at their website here.

Key for numbers generated

Governance indicators

1 (low) = 0 to 2

2 (medium-low) = 3 to 4

3 (medium) = 5 to 6

4 (medium-high) = 7 to 8

5 (high) = 9

Reserve distribution (%)

1 (low) = 0 to 30 %

2 (medium-low) = 30 to 45 %

3 (medium) = 45 to 60 %

4 (medium-high) = 60 to 75 %

5 (high) = 75 %

(Where data are unavailable an arbitrary score of 2 was allocated. For example, Be, As, Na, S, In, Cl, Ca and Ge are allocated a score of 2 since reserve base information is unavailable. Reserve base data are also unavailable for coal; however, reserve data for 2008 are available from the Energy Information Administration (EIA).)

Production Concentration

1 (low) = 0 to 30 %

2 (medium-low) = 30 to 45 %

3 (medium) = 45 to 60 %

4 (medium-high) = 60 to 75 %

5 (high) = 75 %

Crustal Abundance

1 (low) = 100 to 1000 ppm

2 (medium-low) =10 to 100 ppm

3 (medium) = 1 to 10 ppm

4 (medium-high) = 0.1 to 1 ppm

5 (high) = 0.1 ppm

(Where data are unavailable an arbitrary score of 2 was allocated. For example, He is allocated a score of 2 since crustal abundance data is unavailable.)

Explanations for terminology

Crustal Abundance (ppm)

The abundance of an element in the Earth's crust in parts-per-million (ppm) i.e. The number of atoms of this element per 1 million atoms of crust.


The country with the largest reserve base.

Reserve distribution (%)

This is a measure of the spread of future supplies, recording the percentage of a known resource likely to be available in the intermediate future (reserve base) located in the top three countries.

Production Concentrations

This reports the percentage of an element produced in the top three countries. The higher the value, the larger risk there is to supply.

Political stability of top producer

The World Bank produces a global percentile rank of political stability. The scoring system is given below, and the values for all three production countries were summed.

Relative Supply Risk Index

The Crustal Abundance, Reserve distribution (%), Production Concentration and Governance Factor scores are summed and then divided by 2, to provide an overall Relative Supply Risk Index.

Supply risk

Relative supply risk Unknown
Crustal abundance (ppm) Unknown
Recycling rate (%) Unknown
Substitutability Unknown
Production concentration (%) Unknown
Reserve distribution (%) Unknown
Top 3 producers
  • Unknown
Top 3 reserve holders
  • Unknown
Political stability of top producer Unknown
Political stability of top reserve holder Unknown

Oxidation states and isotopes

Key for Isotopes

Half Life
  y years
  d days
  h hours
  m minutes
  s seconds
Mode of decay
  α alpha particle emission
  β negative beta (electron) emission
  β+ positron emission
  EC orbital electron capture
  sf spontaneous fission
  ββ double beta emission
  ECEC double orbital electron capture


Common Oxidation states
The oxidation state of an atom is a measure of the degree of oxidation of an atom. It is defined as being the charge that an atom would have if all bonds were ionic. Free atoms have an oxidation state of 0, and the sum of oxidation numbers within a substance must equal the overall charge.

Important Oxidation states
The most common oxidation states of an element in its compounds.

Elements are defined by the number of protons in its centre (nucleus), whilst the number of neutrons present can vary. The variations in the number of neutrons will create elements of different mass which are known as isotopes.

Oxidation states and isotopes

Common oxidation states 7
Isotopes Isotope Atomic mass Natural abundance (%) Half life Mode of decay
  97Tc 96.906 - 4.2 x 106 EC 
  98Tc 97.907 - 6.6 x 106 β- 
  99Tc 98.906 - 2.13 x 105 β- 

Pressure and temperature - advanced terminology

Specific heat capacity (J kg-1 K-1)

Specific heat capacity is the amount of energy needed to change the temperature of a kilogram of a substance by 1 K.

Young's modulus (GPa)

Young's modulus is a measure of the stiffness of a substance, that is, it provides a measure of how difficult it is to extend a material, with a value given by the ratio of tensile strength to tensile strain.

Shear modulus (GPa)

The shear modulus of a material is a measure of how difficult it is to deform a material, and is given by the ratio of the shear stress to the shear strain.

Bulk modulus (GPa)

The bulk modulus is a measure of how difficult to compress a substance. Given by the ratio of the pressure on a body to the fractional decrease in volume.

Vapour Pressure (Pa)

Vapour pressure is the measure of the propensity of a substance to evaporate. It is defined as the equilibrium pressure exerted by the gas produced above a substance in a closed system.

Pressure and temperature data – advanced

Specific heat capacity
(J kg-1 K-1)
Unknown Young's modulus (GPa) Unknown
Shear modulus (GPa) Unknown Bulk modulus (GPa) Unknown
Vapour pressure  
Temperature (K)
400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
Pressure (Pa)
- - - - - - - - - - -
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Technetium long tantalised chemists because it could not be found. We now know that all its isotopes are radioactive and any mineral deposits of the element had long disappeared from the Earth’s crust. (The longest lived isotope has a half life of 4 million years.) Even so, some technetium atoms are produced as uranium undergoes nuclear fission and there is about 1 milligram of technetium in a tonne of uranium. Claims in the 1920s to have found this element, or at least to have observed its spectrum, cannot be entirely discounted.

Technetium was discovered by Emilio Segrè in 1937 in Italy. He investigated molybdenum from California which had been exposed to high energy radiation and he found technetium to be present and separated it. Today, this element is extracted from spent nuclear fuel rods in tonne quantities.

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Listen to Technetium Podcast
Transcript :

Chemistry in Its Element - Technetium



You're listening to Chemistry in its element brought to you by Chemistry World, the magazine of the Royal Society of Chemistry.


(End promo)


Chris Smith

Hello! For Chemistry in its element this week, we are meeting the man who made the periodic table and also hearing the story of the element that he predicted would exist, but never lived to see it discovered. That man was Mendeleev and with the tale of Technetium, the element he foresaw, here's Mark Peplow.


Mark Peplow

"Once there lived and existed a great learned man, with a beard almost as long as God's", so wrote Daniel Posin in his biography of Dmitri Mendeleev, the 19th Century Russian scientist credited with creating the periodic table of elements. There's a sculpture outside the Slovak University of Technology in Bratislava, which portrays Mendeleev in all his hirsute glory right at the centre of a sunburst of elements. The sculpture makes it clear that Mendeleev is no mere bookkeeper of elements; instead he was the creative spark behind their existence. For a while other scientists had tried to create ways of ordering the known elements. Mendeleev created a system that could predict the existence of elements, not yet discovered. That's what made the idea so revolutionary. When he presented the table to the world in 1869, it contained four prominent gaps, one of these was just below Manganese and Mendeleev predicted an element with atomic weight 43 and properties similar to its neighbours would be found to fill that gap. He named the missing element ekamanganese. After the other absentees were found and subsequently named Scandium, Gallium and Germanium, the search for ekamanganese intensified. There were unconfirmed reports of its discovery from Russia, Japan and most convincingly in Germany, but it was not until 1937 that a group of Italian scientists led by Carlo Perrier and Emilio Segrè at the University of Palermo in Sicily finally found the missing element. The previous year, Segrè had visited Ernest Lawrence's cyclotron in Berkley in America, a particle accelerator that was being used to smash atoms apart. And in early 1937, Lawrence sent Segrè a piece of deflector foil from the cyclotron, made from Molybdenum, element number 42, just one proton shy of ekamanganese. Now Segrè was a particle physicist. He actually went on to share the Nobel Prize in physics for discovering the antiproton. So he didn't have much experience of chemistry, but the mineralogist, Carlo Perrier did and together they eventually managed to isolate two radioactive isotopes of the new element, which they named Technetium. 


The name is from the Greek word for artificial, since Technetium was the very first man-made element, yet despite the name, Technetium is found naturally albeit in tiny traces. It's a product of spontaneous Uranium fission and although there are no stable isotopes of Technetium, you can usually find about a nanogram of Technetium in every 5 kilos of the Uranium ore, pitchblende. That's not to say that the stuff is scarce, it's actually a common waste product from nuclear power stations and it's estimated that several tons of Technetium have been released into the environment as low level waste over the past half century.   But Technetium is also used in about 20 million medical imaging procedures every year. This relies on a form of Technetium, which has a half life of about 6 hours. It decays by emitting a gamma ray, which can be detected by what is effectively a special form of camera. The short half life allows doctors to inject the Technetium into a patient in order to light up particular organs in the body and assess how well they work. Hooking the Technetium atoms up with certain organic molecules or pharmaceuticals can even allow you to target specific types of tissue. Because Technetium doesn't occur naturally, it doesn't interfere with any of the body's biochemistry, so it's safely excreted after the procedure and since you need so little of the isotope, it keeps the radiation dose really low. 


Mendeleev could surely have had no idea that 140 years after he predicted the existence of ekamanganese, about 50,000 people in North America alone would be injected with the stuff every single day.


Chris Smith

Mark Peplow telling the tale of Technetium. Next time on Chemistry in its element we're sinking to new depths.


Philip Ball 

Even the spark of glamour the metal gets from its association with the world's greatest rock band stems from the eeyorish prediction that they would sink like a Lead balloon or zeppelin.


Chris Smith

And you can hear Science Writer, Phil Ball, swinging the Lead in next week's edition of Chemistry in its element. I'm Chris Smith, thank you for listening.   See you next time.




Chemistry in its elementis brought to you by the Royal Society of Chemistry and produced by thenakedscientists dot com. There's more information and other episodes of Chemistry in its element on our web site at chemistryworld dot org forward slash elements.


(End promo) 

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Visual Elements images and videos
© Murray Robertson 2011.



W. M. Haynes, ed., CRC Handbook of Chemistry and Physics, CRC Press/Taylor and Francis, Boca Raton, FL, 95th Edition, Internet Version 2015, accessed December 2014.
Tables of Physical & Chemical Constants, Kaye & Laby Online, 16th edition, 1995. Version 1.0 (2005), accessed December 2014.
J. S. Coursey, D. J. Schwab, J.J. Tsai, and R. A. Dragoset, Atomic Weights and Isotopic Compositions(version 3.0), 2010, National Institute of Standards and Technology, Gaithersburg, MD, accessed December 2014.
T. L. Cottrell, The Strengths of Chemical Bonds, Butterworth, London, 1954.


Uses and properties

John Emsley, Nature’s Building Blocks: An A-Z Guide to the Elements, Oxford University Press, New York, 2nd Edition, 2011.
Thomas Jefferson National Accelerator Facility - Office of Science Education, It’s Elemental - The Periodic Table of Elements, accessed December 2014.
Periodic Table of Videos, accessed December 2014.


Supply risk data

Derived in part from material provided by the British Geological Survey © NERC.


History text

© John Emsley 2012.



Produced by The Naked Scientists.


Periodic Table of Videos

Created by video journalist Brady Haran working with chemists at The University of Nottingham.