Periodic Table > Hafnium
 

Terminology


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


For more information on Murray Robertson’s image see Uses/Interesting Facts below.

 

Fact Box Terminology


Group
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.


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


Block
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.


Isotopes
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.


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


Density (kgm-3)
Density is the weight of a substance that would fill 1 m3 (at 298 K unless otherwise stated).


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 2233 oC, 4051.4 oF, 2506.15 K 
Period Boiling point 4600 oC, 8312 oF, 4873.15 K 
Block Density (kg m-3) 13276 
Atomic number 72  Relative atomic mass 178.49  
State at room temperature Solid  Key isotopes 177Hf, 178Hf, 180Hf 
Electron configuration [Xe] 4f145d26s2  CAS number 7440-58-6 
ChemSpider ID 22422 ChemSpider is a free chemical structure database
 

Interesting Facts 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.


Appearance

The description of the element in its natural form.

Uses / Interesting Facts

 
Image explanation
An image based on the civic coat of arms for the city of Copenhagen.
Appearance
A shiny silvery metal that resists corrosion. Its alloys are used to make control rods for nuclear reactors because it will absorb neutrons and has a very high melting point.
Uses
Hafnium has a good thermal absorption cross-section for neutrons, so is used in control rods in nuclear reactors. It has been successfully alloyed with several metals including iron, titanium and niobium. It is also used in gas-filled and incandescent lights.
Biological role
Hafnium has no known biological role, and is non-toxic.
Natural abundance
Most zirconium minerals contain 1-5% hafnium, and the metal is prepared by reducing the tetrachloride with sodium or magnesium.
 
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) 2.230 Covalent radius (Å) 1.64
Electron affinity (kJ mol-1) 1.64 Electronegativity
(Pauling scale)
1.300
Ionisation energies
(kJ mol-1)
 
1st
658.519
2nd
1447.279
3rd
2248.106
4th
3215.854
5th
-
6th
-
7th
-
8th
-
 

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 base 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.


Sourced

The country with the largest reserve base.


Reserve Base 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.


Total Governance Factor

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 Base Distribution, Production Concentration and Governance Factor scores are summed and then divided by 2, to provide an overall Relative Supply Risk Index.

Supply Risk

 
Scarcity factor Unknown
Country with largest reserve base Unknown
Crustal abundance (ppm) Unknown
Leading producer Unknown
Reserve base distribution (%) Unknown
Production concentration (%) Unknown
Total governance factor(production) Unknown
Top 3 countries (mined)
  • Unknown
Top 3 countries (production)
  • Unknown
 

Oxidation states/ 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

Terminology


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.


Isotopes
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 / Isotopes

 
Common oxidation states 4
Isotopes Isotope Atomic mass Natural abundance (%) Half life Mode of decay
  174Hf 173.94 0.16 2.0 x 1015
  176Hf 175.941 5.26
  177Hf 176.943 18.6
  178Hf 177.944 27.28
  179Hf 178.946 13.62
  180Hf 179.947 35.08
 

Pressure and Temperature - Advanced Terminology


Molar Heat Capacity (J mol-1 K-1)

Molar heat capacity is the energy required to heat a mole 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 / Temperature - Advanced

 
Molar heat capacity
(J mol-1 K-1)
25.73 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)
- - - - - 1.35
x 10-11
9.81
x 10-9
1.63
x 10-6
9.69
x 10-5
2.72
x 10-3
4.37
x 10-2
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History

In 1911, Georges Urbain reported the discovery of the missing element below zirconium in the periodic table, but he was wrong and the search continued. It was finally discovered by George Charles de Hevesy and Dirk Coster at the University of Copenhagen in 1923. It was found in a zirconium mineral, a Norwegian zircon, but it had proved very difficult to separate it from zirconium and this explained why hafnium remained undiscovered for so long.


Other zirconium minerals were now examined by Hevesy, and some were found to contain as much as five per cent of hafnium. (It meant the atomic weight of zirconium was wrong and hafnium-free material had to be produced in order for this to be determined.)


The first pure sample of hafnium itself was made in 1925 by decomposing hafnium tetra-iodide over a hot tungsten wire.

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Podcasts

Listen to Hafnium Podcast
Transcript :

Chemistry in Its Element - Hafnium


  (Promo)

 

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

(End promo)

 

Meera Senthilingam

 

This week, super alloys, nuclear reactors and space rockets.   Just some of the reasons that this week's uncommon and unknown element Hafnium is cherished by scientists worldwide.   Here's Eric Scerri. 

 

Eric Scerri

 

Today I am going to talk about an uncommon element that is also not very well known.   However it has a rather interesting history and some important commercial applications including its use in the nuclear power industry and in the making of super-alloys.

             The element is number 72 in the periodic table, and is called hafnium.   It takes its name from hafnium, the old Latin name for Copenhagen which is the city in which it was first isolated in 1922.   But first let me back-track a little.   In 1913, the physicist Henry Moseley, working in Manchester and later Oxford, discovered an experimental method for ordering the elements according to their atomic numbers.   Prior to this work the elements in the periodic table had been ordered by using their atomic weights, which gave rise to a series with uneven gaps between each element.   As a result, nobody could be sure how many elements remained to be discovered.   All this changed following Moseley's discovery because atomic number increases in whole number steps as one moves through the periodic table.  

             One of the gaps that opened up, was between element 71, lutetium, and element 73, tantalum.   Moreover this particular case was complicated by the fact that it was not clear if element 72 would turn out to be a transition metal, or perhaps a rare earth element, since element 72 falls at the boundary between these two types of elements.   Some chemists thought the element would be a rare earth element and carried out many fruitless searches for the element among minerals containing rare earths.   But some other chemists suggested that the new element would be a transition metal.   The chemical argument for this was quite simple.   According to some versions of the periodic table, element 72 fell underneath titanium and zirconium in the periodic table, and both of these elements were known transition elements.   Then an argument from physics was proposed by Niels Bohr, one of the founders of quantum theory.   According to the electronic configuration that Bohr predicted for element 72 he also agreed that it had be a transition metal.  

             In 1923 Coster and Hevesy a couple of young researchers in Bohr's institute decided to try to isolate the element as a test of Bohr's theory.   In order to do this they followed the chemists' suggestion and decided to look among the ores of zirconium.   Within just a few weeks they succeeded by examining some Norwegian zircon and by detecting the X-ray spectral line frequencies expected for this element.   It was the discovery of one of the only six then remaining gaps in the periodic table.   It also turned out to be the one but last discovery of any naturally occurring element, the last one being rhenium a few years later.  

             Hafnium is not all that uncommon compared to many other exotic elements.   It occurs to the extent of 5.8 ppm of the Earth's upper crust by weight.   The reason why it took a long time to isolate is that its atoms have almost the identical size to those of zirconium, along with which it typically occurs in minerals.   This makes it difficult to separate from zirconium.   But these days a number of methods of extraction have been developed and hafnium has found many of applications because of its rather specific properties.   It is a shiny, silvery metal that is corrosion resistant to a remarkable degree.   More important perhaps, it has a very high ability to capture neutrons which renders it ideal for making control rods in nuclear reactors, especially those that need to operate under harsh conditions such as today's pressurized water reactors.

             Hafnium is also very good at forming super-alloys, which can withstand very high temperatures and has found applications in making a variety of parts for space vehicles.   In terms of regular compounds rather than alloys, hafnium carbide has the highest melting point, of any compound consisting of just two elements, at just under 

3,9900C.   Moving up to compounds of three elements, the mixed carbide of tungsten and hafnium has the single highest melting point of any known compound at 41250C.  

             Hafnium is not cheap given how difficult it is to extract and because of its relative scarcity.   But there are some cases where one just has to pay the price!   In the case of nuclear reactors for example, it costs in excess of a million dollars just for the neutron absorbing hafnium rods.  

             On my recent trip to Copenhagen I spent a long time looking for the famous little mermaid that is symbolic of the city.   When I found it I was surprised to see that it is rather insignificant but this did not seem to lessen the special attention that it held from tourists from all over the world.   I think it's a little bit like the metal hafnium, first discovered in the mermaid's city of Copenhagen.   It too seems somewhat insignificant at first sight and yet it holds the attention of a variety of scientists because of its rather special properties.  

       

Meera Senthilingam

 

The ability to capture neutrons and the highest melting point of any compound, you can see why scientists consider this element as special as the little mermaid.   That was Eric Scerri revealing the powers of Hafnium.   Now next week, we meet the King of the elements.  

 

 

 

Brian Clegg

 

Forget 10 Downing Street or 1600 Pennsylvania Avenue, the most prestigious address in the universe is number one in the periodic table, hydrogen. In science, simplicity and beauty are often equated - and that makes hydrogen as beautiful as they come, a single proton and a lone electron making the most compact element in existence.

 

Meera Senthilingam

 

And Brian Clegg will be revealing the beauty of Hydrogen in next week's Chemistry in its Element.   Until then, thanks for listening, I'm Meera Senthilingam from the nakedscientists.com and I'll see you next week.  

 

 (Promo)

 

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 website at chemistryworld dot org forward slash elements. 

 

(End promo)

 

 

 

 

 

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Resources

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Assessment for Learning is an effective way of actively involving students in their learning. This is a series of plans based around chemistry topics.
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In this experiment you will be looking at a group of transition elements chromium, molybdenum and tungsten.
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The purpose of this experiment is to examine some of the solution chemistry of the transition elements.
 

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References

 
Images:  Visual Elements © Murray Robertson 2011
Mining and Sourcing data:  British Geological Survey – natural environment research council.
Text:  John Emsley Nature’s Building Blocks: An A-Z Guide to the Elements, Oxford University Press, 2nd Edition, 2011.
Additional information for platinum, gold, neodymium and dysprosium obtained from Material Value Consultancy Ltd www.matvalue.com
Data: CRC Handbook of Chemistry and Physics, CRC Press, 92nd Edition, 2011.
G. W. C. Kaye and T. H. Laby Tables of Physical and Chemical Constants, Longman, 16th Edition, 1995.
Members of the RSC can access these books through our library.