Periodic Table > Palladium
 

Terminology


Allotropes
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


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 10  Melting point 1554.8 oC, 2830.64 oF, 1827.95 K 
Period Boiling point 2963 oC, 5365.4 oF, 3236.15 K 
Block Density (kg m-3) 11995 
Atomic number 46  Relative atomic mass 106.42  
State at room temperature Solid  Key isotopes 106Pd 
Electron configuration [Kr] 4d10  CAS number 7440-05-3 
ChemSpider ID 22380 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.


Appearance

The description of the element in its natural form.

Uses and properties

 
Image explanation
The image represents the asteroid Pallas, after which the element is named. In the background are 20th-century star charts.
Appearance
A shiny, silvery-white metal that resists corrosion.
Uses
Most palladium is used in catalytic converters for cars. It is also used in jewellery and some dental fillings and crowns. White gold is an alloy of gold that has been decolourised by alloying with another metal, sometimes palladium.

It is used in the electronics industry in ceramic capacitors, found in laptop computers and mobile phones. These consist of layers of palladium sandwiched between layers of ceramic.

Finely divided palladium is a good catalyst and is used for hydrogenation and dehydrogenation reactions. Hydrogen easily diffuses through heated palladium and this provides a way of separating and purifying the gas.
Biological role
Palladium has no known biological role. It is non-toxic.
Natural abundance
Palladium has been found uncombined in nature, in Brazil, but most is found in sulfide minerals such as braggite. It is extracted commercially as a by-product of nickel refining. It is also extracted as a by-product of copper and zinc refining.
 
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) 2.100 Covalent radius (Å) 1.3
Electron affinity (kJ mol-1) 54.206 Electronegativity
(Pauling scale)
2.200
Ionisation energies
(kJ mol-1)
 
1st
804.388
2nd
1874.709
3rd
3177.260
4th
-
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 8.5
Country with largest reserve base South Africa
Crustal abundance (ppm) 3.7E-05
Leading producer South Africa
Reserve base distribution (%) 87.50
Production concentration (%) 58.80
Total governance factor(production) 7
Top 3 countries (mined)
  • 1) South Africa
  • 2) Russia
  • 3) USA
Top 3 countries (production)
  • 1) South Africa
  • 2) Russia
  • 3) USA
 

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

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 and isotopes

 
Common oxidation states 4, 2, 0
Isotopes Isotope Atomic mass Natural abundance (%) Half life Mode of decay
  102Pd 101.906 1.02
  104Pd 103.904 11.14
  105Pd 104.905 22.33
  106Pd 105.903 27.33
  108Pd 107.904 26.46
  110Pd 109.905 11.72
 

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 and temperature data – advanced

 
Molar heat capacity
(J mol-1 K-1)
25.98 Young's modulus (GPa) Unknown
Shear modulus (GPa) Unknown Bulk modulus (GPa) 182
Vapour pressure  
Temperature (K)
400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
Pressure (Pa)
- - - 8.27
x 10-9
1.40
x 10-5
2.77
x 10-3
0.14 3.07 30.4 - -
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History

As early as 1700, miners in Brazil were aware of a metal they called ouro podre, ‘worthless gold,’ which is a native alloy of palladium and gold. However, it was not from this that palladium was first extracted, but from platinum, and this was achieved in 1803 by William Wollaston. He noted that when he dissolved ordinary platinum in aqua regia (nitric acid + hydrochloric acid) not all of it went into solution.


It left a residue from which he eventually extracted palladium. He did not announce his discovery but put the new metal on sale as a ‘new silver’. Richard Chenevix purchased some, investigated it, and declared it to be an alloy of mercury and platinum. In February 1805 Wollaston revealed himself as its discoverer and gave a full and convincing account of the metal and its properties.

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Podcasts

Listen to Palladium Podcast
Transcript :

Chemistry in Its Element - Palladium


  (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, an element whose discovery was announced in a very unique way. So to explain more above the discovery and chemistry of palladium, here's Simon Cotton.

 

Simon Cotton 

For the first 5 years of my life, I lived in the Norfolk market town that was the birthplace of the discoverer of palladium, William Hyde Wollaston.

When he isolated this metal in 1802, he did something quite unique. Instead of announcing it in a reputable scientific journal, he described its properties in an anonymous leaflet, displayed in the window of a shop in Gerrard Street, Soho, in April 1803.

Entitled 'PALLADIUM; OR, NEW SILVER', this handbill described properties of the new element, giving its density and several of its chemical properties, concluding with the announcement that it was sold only at that shop 'In Samples of Five Shillings, Half a Guinea & One Guinea each.'

No one was able to refute Wollaston's claim for a new element, but it was not until 1805 that he published his discovery in a scientific journal.

Palladium is a remarkable metal, not least because it will absorb over 900 times its volume of hydrogen gas. The hydrogen is released again when the metal is heated, so this can be a rather cunning way of weighing hydrogen. And because palladium won't absorb any other gas, you can use this property to purify hydrogen.

At the bottom of our hearts, we know that the age of cheap energy is over. Quite apart from worries about the greenhouse effect and global warming, oil is running out, and the search is on for green alternatives, and palladium is concerned in the most controversial claim that has been made in this area.

Life on Earth relies on the sun. The sun produces energy by fusing hydrogen atoms together to produce helium, a process that requires extremely high temperatures. On March 23 1989, two scientists working in the USA, Martin Fleischmann and Stanley Pons, reported results of room-temperature electrolysis of heavy water using a platinum anode and a palladium cathode. They claimed to have produced excess energy, and suggested that it arose from nuclear fusion reactions. This was seen as a source of cheap energy, possibly solving the world's energy problems.

When hydrogen molecules first come into contact with palladium, they are adsorbed on the surface, but then they diffuse throughout the metal. In palladium saturated with hydrogen, the molecules are extremely close together. Fleischmann and Pons believed that this closeness had led to the energy-producing nuclear fusion reactions happening. Over the last twenty years, no one has been able to reproduce this, and the reaction has passed into the realms of Voodoo Science.

Palladium does however have a genuine use in 'green' energy, as a catalyst in hydrogen fuel cells. Palladium is one of a number of metals starting to be used in the fuel cells to power a host of things including cars and buses.

Palladium is also widely used in catalytic reactions in industry, such as in hydrogenation of unsaturated hydrocarbons, as well as in jewellery and in dental fillings and crowns.

But the main use of palladium, along with rhodium and platinum, is in the three-way catalytic converters in car exhaust systems. Untreated, car exhaust fumes contain several undesirable gases, and the purpose of the catalytic converters is to eliminate them. They are called three-way converters as they reduce three types of harmful emissions. Converting toxic carbon monoxide into carbon dioxide; the hydrocarbons in unburned fuel into carbon dioxide and water; and toxic oxides of nitrogen (which can contribute to smog and acid rain) into harmless nitrogen gas.

So, that's palladium - a metal with humble beginnings that now plays a major role in industrial catalysis, powering and cleaning up after our vehicles and even makes the occasional appearance in our jewellery boxes, and even in our mouths. 

 

Meera Senthilingam

Quite the catalyst that palladium! Providing energy in fuel cells, protecting our environment through catalytic converters, and providing aesthetic pleasure in jewellery and even dentistry. That was Simon Cotton, from Uppingham School in the UK, with the chemistry of palladium. 

Next week, an element that certainly doesn't deserve to be called boring.

 

Louise Natrajan

There is a famous quote about the lanthanides by Pimentel and Sprately from their book, Understanding Chemistry published in 1971:
'Lanthanum has only one important oxidation state in aqueous solution, the +3 state. With few exceptions, this tells the whole boring story about the other 14 elements.'

If you've listened to any other of the podcasts in the lanthanide series, I hope you'll agree that this is far from true. While, the most common oxidation state of the lanthanides is indeed the +3 valence state, ytterbium, the last and smallest of the lanthanides or rare earths in the series is one of the exceptions Pimentel and Sprately were talking about.

 

Meera Senthilingam

And Louise Natrajan will be revealing the true - exciting - nature of ytterbium that makes it one of the exceptions, in next week's Chemistry in its element. Until then, I'm Meera Senthilingham, and thank you for listening.

 

(Promo)

 

Chemistry in its element is 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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In this experiment you will be looking at a group of transition elements chromium, molybdenum and tungsten.
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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.