Some elements exist in several different structural forms, called allotropes. Each allotrope has different physical properties.

For more information on the Visual Elements image see the Uses and properties section below.



A vertical column in the periodic table. Members of a group typically have similar properties and electron configurations in their outer shell.

A horizontal row in the periodic table. The atomic number of each element increases by one, reading from left to right.

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 (s), principal (p), diffuse (d), and fundamental (f).

Atomic number
The number of protons in an atom.

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

Melting point
The temperature at which the solid–liquid phase change occurs.

Boiling point
The temperature at which the liquid–gas phase change occurs.

The transition of a substance directly from the solid to the gas phase without passing through a liquid phase.

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.

Atoms of the same element with different numbers of 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.

Fact box

Group Melting point 2157°C, 3915°F, 2430 K 
Period Boiling point 4262°C, 7704°F, 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


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.


The description of the element in its natural form.

Biological role

The role of the element in humans, animals and plants.

Natural abundance

Where the element is most commonly found in nature, and how it is sourced commercially.

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.
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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.

Atomic radius, non-bonded
Half of the distance between two unbonded atoms of the same element when the electrostatic forces are balanced. These values were determined using several different methods.

Covalent radius
Half of the distance between two atoms within a single covalent bond. Values are given for typical oxidation number and coordination.

Electron affinity
The energy released when an electron is added to the neutral atom and a negative ion is formed.

Electronegativity (Pauling scale)
The tendency of an atom to attract electrons towards itself, expressed on a relative scale.

First ionisation energy
The minimum energy required to remove an electron from a neutral atom in its ground state.

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)


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. Uncombined elements have an oxidation state of 0. The sum of the oxidation states within a compound or ion must equal the overall charge.


Atoms of the same element with different numbers of neutrons.

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

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- 


Data for this section been provided by the British Geological Survey.

Relative supply risk

An integrated supply risk index from 1 (very low risk) to 10 (very high risk). This is calculated by combining the scores for crustal abundance, reserve distribution, production concentration, substitutability, recycling rate and political stability scores.

Crustal abundance (ppm)

The number of atoms of the element per 1 million atoms of the Earth’s crust.

Recycling rate

The percentage of a commodity which is recycled. A higher recycling rate may reduce risk to supply.


The availability of suitable substitutes for a given commodity.
High = substitution not possible or very difficult.
Medium = substitution is possible but there may be an economic and/or performance impact
Low = substitution is possible with little or no economic and/or performance impact

Production concentration

The percentage of an element produced in the top producing country. The higher the value, the larger risk there is to supply.

Reserve distribution

The percentage of the world reserves located in the country with the largest reserves. The higher the value, the larger risk there is to supply.

Political stability of top producer

A percentile rank for the political stability of the top producing country, derived from World Bank governance indicators.

Political stability of top reserve holder

A percentile rank for the political stability of the country with the largest reserves, derived from World Bank governance indicators.



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

A measure of the stiffness of a substance. 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

A measure of how difficult it is to deform a material. It is given by the ratio of the shear stress to the shear strain.

Bulk modulus

A measure of how difficult it is to compress a substance. It is given by the ratio of the pressure on a body to the fractional decrease in volume.

Vapour pressure

A 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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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 element is brought to you by the Royal Society of Chemistry and produced by There's more information and other episodes of Chemistry in its element on our website at

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Visual Elements images and videos
© Murray Robertson 1998-2017.



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 4.1), 2015, National Institute of Standards and Technology, Gaithersburg, MD, accessed November 2016.
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

Elements 1-112, 114, 116 and 117 © John Emsley 2012. Elements 113, 115, 117 and 118 © Royal Society of Chemistry 2017.



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