Glossary
Allotropes
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.
| Discovery date | 1839 |
| Discovered by | Carl Gustav Mosander |
| Origin of the name | The name is derived from the Greek 'lanthanein', meaning to lie hidden. |
| Allotropes |
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Glossary
Group
A vertical column in the periodic table. Members of a group typically have similar properties and electron configurations in their outer shell.
Period
A horizontal row in the periodic table. The atomic number of each element increases by one, reading from left to right.
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 (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.
Sublimation
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.
Isotopes
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.
| Group | Lanthanides | Melting point | 920°C, 1688°F, 1193 K |
| Period | 6 | Boiling point | 3464°C, 6267°F, 3737 K |
| Block | d | Density (g cm−3) | 6.15 |
| Atomic number | 57 | Relative atomic mass | 138.905 |
| State at 20°C | Solid | Key isotopes | 139La |
| Electron configuration | [Xe] 5d16s2 | CAS number | 7439-91-0 |
| ChemSpider ID | 22369 | ChemSpider is a free chemical structure database | |
Glossary
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.
Appearance
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.
History
History
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.
Glossary
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.
Isotopes
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 | |
Glossary
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.
Substitutability
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.
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Glossary
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.
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Specific heat capacity (J kg−1 K−1) |
195 | Young's modulus (GPa) | 36.6 | |||||||||||
| Shear modulus (GPa) | 14.3 | Bulk modulus (GPa) | 27.9 | |||||||||||
| Vapour pressure | ||||||||||||||
| Temperature (K) |
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| Pressure (Pa) |
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Podcasts
Podcasts
| Listen to Lanthanum Podcast |
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Transcript :
Chemistry in its element: lanthanum (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 Hello and welcome to Chemistry in its Element, I'm Meera Senthilingam. This week the element that resembles a humble, but crucial film star, that appears everywhere but is often forgotten about. Brian Clegg uncovers the secret world of Lanthanum. Brian Clegg The periodic table is a wonderful structure. In its neat, ordered way, it predicts the behaviour of atoms as they follow a step-by-step pattern of increasing atomic number. At first glance, it's a simple matter of running across row after row. But take a closer look at barium and its obscure neighbour to the right, hafnium. Barium is atomic number 56. hafnium is 72. There are 15 elements missing. On a modern table, these appear at the bottom in a separate, floating row. They are the lanthanides - and we're taking a look at the element that gave its name to the whole group, lanthanum. For most of us, giving the name to that group is about all lanthanum is known for - so it comes as quite a surprise to discover just how many ways it is used - we'll find it everywhere from cameras to swimming pools. But before we uncover the secret world of lanthanum, how did it end up sounding like a Victorian opium drink? It was one of the earlier lanthanides to be discovered, by the Swedish scientist Carl Gustav Mosander, working at the famous Karolinska Institute in 1839, though it was 1923 before the pure metal was produced. One of the most reactive of the lanthanides, readily oxidising and bubbling away in water, lanthanum turned up unexpectedly in a cerium salt sample Mosander was working on. It was because of its sneakily unexpected appearance in the sample that Mosander called it lanthanum, from the Greek word lanthano, meaning to escape notice - in fact the first recorded reference to it in 1841 calls it 'another metallic oxide, which has hitherto lain concealed in oxide of cerium'. When it comes to using lanthanum, it best resembles a successful movie bit part player. Someone who never gets the lead role, but appears in film after film, solidly portraying different characters. Not a particularly expensive material to produce, lanthanum's many roles remain of a supporting kind, playing an essential part but avoiding the limelight. It is often added in small quantities to metals like iron and steel to make them less brittle, or to tungsten to improve the quality of electrodes used in arc welding. On a lesser scale of heat it also contributes to the spark produced by cigarette lighters using a material called mischmetal (literally mix metal in German) at least a quarter of which is usually lanthanum, giving the element its one starring role. Much of the lanthanum we experience is invisible, incorporated into glass. For many years, lead has been added to glass to give it an increased refractive index, producing an extra-shiny crystal effect. As the refractive index goes up, light travels slower in the material and the light is bent more as it travels from air into the glass. Lanthanum is much better than lead at pushing up the refractive index without dispersing the light too much, this extra clarity means that lanthanum oxide is now used widely in lenses for cameras and telescopes. Some of those lenses will be pointed at celebrity swimming pools, where one of the many chemicals likely to be added to the water is a lanthanum salt, aimed at latching onto phosphates that would otherwise act as in-water fertiliser, encouraging green algae to discolour the pool. And I could go on about its use in rechargeable Nickel Metal Hydride batteries or gas mantles - but I'm sure you get the point. Lanthanum may be useful for scanning distant views through binoculars, but a final use of the element is in peering into the past. We're familiar with radiocarbon dating, based on the decay rate of carbon 14, being used to date biological specimens. Such radiometric dating relies on the fact that radioactive materials decay with a known half life. This means that, for instance, with carbon 14, half of the original amount will be left after around 6,000 years. The remainder will half again in the next 6,000 years, and so on. By measuring the amount of the radioactive substance in an object, relative to the product of its decay, we can determine its age. But to use carbon dating we need something with a reasonable amount of carbon in it - usually something that was originally living - and for the object to have been formed no more than about 60,000 years ago, after which too little of the carbon 14 is left. This makes it useless when attempting to date rocks that are hundreds of millions of years old. Here, one of the alternative dating approaches is so called La-Ba dating. Lanthanum and the element before it in the periodic table, barium, have an exotic relationship. Barium 139, for example, has a half-life of just 68 minutes before it breaks down to form lanthanum 139 - not suitable for dating anything older than a loaf of bread. But lanthanum 138 has a hefty half-life of around 100 billion years on the way to forming barium 138, making it ideal for dating ancient granites. Working on these timescales makes for a fairly loose idea of accuracy. One paper on the La-Ba technique proudly announces that rocks have been dated 'with the high precision of plus or minus 3.7 million years'. This is not the kind of accuracy we hope for in train timetables, but when you're dealing with something half a billion years old, it makes a pretty good hit for lanthanum, the element that despite its name, shouldn't escape notice. Meera Senthilingam So it makes metal stronger, camera lenses better and keeps swimming pools clean. This element really does like to get around. That was Brian Clegg with the hidden depths of lanthanum. Next week an element that may appear just normal or indistinct but is truly adored by the people that know it - a trait it seems to share with a famous mermaid. Eric Scerri 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 for tourists from all over the world. I think it's a bit like the metal hafnium, first discovered in the mermaid's city of Copenhagen. It too seems rather insignificant at first sight and yet it holds the attention of a variety of scientists because of its rather special properties. Meera Senthilingam And you can learn the history and uses of Hafnium that make this element so loved by scientists worldwide with Eric Scerri in next week's Chemistry in its element. I'm Meera Senthilingam, thank you for listening and see you next week. (Promo) Chemistry in its element is brought to you by the Royal Society of Chemistry and produced by thenakedscientists.com. There's more information and other episodes of Chemistry in its element on our website at chemistryworld.org/elements. (End promo)
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Video
Video
Resources
Resources
Terms & Conditions
Images © Murray Robertson 1999-2011
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Data
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.
Podcasts
Produced by The Naked Scientists.
Periodic Table of Videos
Created by video journalist Brady Haran working with chemists at The University of Nottingham.
