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.

 

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.


Fact box

 
Group 13  Melting point 2077°C, 3771°F, 2350 K 
Period Boiling point 4000°C, 7232°F, 4273 K 
Block Density (g cm−3) 2.34 
Atomic number Relative atomic mass 10.81  
State at 20°C Solid  Key isotopes 11
Electron configuration [He] 2s22p1  CAS number 7440-42-8 
ChemSpider ID 4575371 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.

Uses and properties

 
Image explanation
An image reflecting the importance of boron as an essential mineral for plants. The tree and its strange metallic foliage ‘grow’ from a ‘pure’ dark powdered cone of the element.
Appearance
Pure boron is a dark amorphous powder.
Uses
Amorphous boron is used as a rocket fuel igniter and in pyrotechnic flares. It gives the flares a distinctive green colour.

The most important compounds of boron are boric (or boracic) acid, borax (sodium borate) and boric oxide. These can be found in eye drops, mild antiseptics, washing powders and tile glazes. Borax used to be used to make bleach and as a food preservative.

Boric oxide is also commonly used in the manufacture of borosilicate glass (Pyrex). It makes the glass tough and heat resistant. Fibreglass textiles and insulation are made from borosilcate glass.

Sodium octaborate is a flame retardant.

The isotope boron-10 is good at absorbing neutrons. This means it can be used to regulate nuclear reactors. It also has a role in instruments used to detect neutrons.
Biological role
Boron is essential for the cell walls of plants. It is not considered poisonous to animals, but in higher doses it can upset the body’s metabolism. We take in about 2 milligrams of boron each day from our food, and about 60 grams in a lifetime. Some boron compounds are being studied as a possible treatment for brain tumours.
Natural abundance
Boron occurs as an orthoboric acid in some volcanic spring waters, and as borates in the minerals borax and colemanite. Extensive borax deposits are found in Turkey. However, by far the most important source of boron is rasorite. This is found in the Mojave Desert in California, USA.

High-purity boron is prepared by reducing boron trichloride or tribromide with hydrogen, on electrically heated filaments. Impure, or amorphous, boron can be prepared by heating the trioxide with magnesium powder.
 
Glossary

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) 1.92 Covalent radius (Å) 0.84
Electron affinity (kJ mol−1) 26.989 Electronegativity
(Pauling scale)
2.04
Ionisation energies
(kJ mol−1)
 
1st
800.637
2nd
2427.069
3rd
3659.751
4th
25025.905
5th
32826.802
6th
-
7th
-
8th
-
 

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.


Supply risk

 
Relative supply risk 4.5
Crustal abundance (ppm) 11
Recycling rate (%) Unknown
Substitutability Unknown
Production concentration (%) 33.6
Reserve distribution (%) Unknown
Top 3 producers
  • 1) Turkey
  • 2) USA
  • 3) Chile
Top 3 reserve holders
  • 1) Turkey
  • 2) Russia
  • 3) USA
Political stability of top producer 11.8
Political stability of top reserve holder 11.8
 

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

Oxidation states and isotopes

 
Common oxidation states 3
Isotopes Isotope Atomic mass Natural abundance (%) Half life Mode of decay
  10B 10.013 19.9
  11B 11.009 80.1
 

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.

Pressure and temperature data – advanced

 
Specific heat capacity
(J kg−1 K−1)
1026 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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History

For centuries the only source of borax, Na2B2O5(OH)4, was the crystallized deposits of Lake Yamdok Cho, in Tibet. It was used as a flux used by goldsmiths.

In 1808, Louis-Josef Gay-Lussac and Louis-Jacques Thénard working in Paris, and Sir Humphry Davy in London, independently extracted boron by heating borax with potassium metal. In fact, neither had produced the pure element which is almost impossible to obtain. A purer type of boron was isolated in 1892 by Henri Moissan. Eventually, E. Weintraub in the USA produced totally pure boron by sparking a mixture of boron chloride, BCl3 vapour, and hydrogen. The material so obtained boron was found to have very different properties to those previously reported.
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Podcasts

Listen to Boron Podcast
Transcript :

Chemistry in its element: boron


(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 we see the true nature of an element wrongly accused of being boring. I'm Meera Senthilingam from the Naked Scientists.com, and to see how a supposed dreary element can indulge in swinging antics and numerous adventures here's Pat Bailey with the brighter side of boron.

Pat Bailey

If I had to choose a person to represent gold, then I guess it might be an ambitious young stockbroker, a bit flashy, and not great at forming relationships. For helium - an airy-fairy blonde with a bit of a squeaky voice, but with aspirations to join the nobility.

And for boron? Well at first glance, during the working week at any rate, a boring, middle-aged accountant, maybe wearing brown corduroys and a tweed jacket . but with an unexpected side-to him in his spare time - skydiving, motorbiking, and a member of a highly dubious society that indulges in swapping partners.

Let's start with the boring bit. Boron is usually isolated as a brown, amorphous solid. I don't know anyone who thinks the element boron has anything interesting about it. But its unexpected side starts to emerge when you look at some simple compounds of boron. Consider the nitride, for example - just the 2 elements at numbers 5 and 7 in the periodic table, but able to join forces to provide hard diamond or soft graphite-like structures, very similar to those of the 6th element, carbon. Then there is the trifluoride - remember that acids were first classified as substances that could provide protons, but BF3 is the archetypal Lewis acid, which doesn't have a proton in sight, yet is able to coordinate with lone pairs, allowing it to catalyse an array of reactions. It can achieve this chemistry because boron really does have two sides to it - it is set up to form 3 bonds with adjacent atoms, but even in this state, readily forms an extra bond in order to complete the 2nd main shell of 8 electrons . but when it does this, it acquires a negative charge, and it can only regain neutrality by losing one of its bonds - it really does have a split personality.

But the real interest, the 'skydiving', starts when we look at the trihydride of boron. We'll return to this later on, as BH3 has structural subtleties that will really take us into sexy territory. But at this stage we'll simply see how boron's schizophrenic side can be used to good effect - add BH3 to an alkene, then throw in some alkaline hydrogen peroxide, and the oxygen first attaches to the boron, and then gets shuttled onto the adjacent carbon, all driven by this balance between 3- and 4-valent boron. This rather complicated reaction (mechanistically) is very reliable, and has been used for decades now as a simple way of turning alkenes into alcohols. Building on this idea, lots of clever variants allow one to introduce the alcohol very selectively, including my favourite of the reagent made by reacting borane with cycloocta-1,5-diene; the resulting dialkylborane is incredibly selective at attacking only the least substituted carbon of an alkene, and its often abbreviated schematically to a BH unit hanging down from two arcs, leading to its nickname as the parachute molecule.

So much for skydiving - what about motorbikes. Well this bit is rather like seeing what appears to be a 50cc moped, only to find that it goes from 0-to-60 in 3.5 seconds. Let me explain - the name boron comes from the mineral borax, which is a salt of the a really uninspiring acid called boracic acid. You can buy it from any pharmacist, and it's a mildly acidic antiseptic, and it essentially comprises a boron atom attached to three OH groups. And here's the surprise - you can fairly easily swap one OH for an aryl group, and you generate an aryl boronic acid capable of coupling to a whole range of aryl halides using palladium catalysis. This was a long sought-after process that many had thought impossible in high yield, until a chemist called Suzuki (hence the motorbike connection) found that boron could solve the trick.

And lastly to the sexy bit. I said that boron trihydride had a structural subtlety, and that is the fact that it was an 'impossible' molecule back in 1945, in that there was no known bonding that could account for its dimeric structure, or that of some related boron hydrides. And then in one of those 'Just William' sort of stories when a youngster gets the better of his elders, Christopher Longuet-Higgins, then an undergraduate at Cambridge, came up with the solution during a tutorial, publishing the landmark paper with his tutor whilst still only 20. Their explanation also predicted several new boron hydrides, which were duly discovered, as well as the fascinating field of boron cluster chemistry, in which the tri/tetra-valent schizophrenia of boron allows partner swaps and multiple bonding . but I won't elaborate further - you'll have to find out for yourself. But remember, don't just judge elements by their first appearance - they may have hidden secrets and unexpected talents.

Meera Senthilingam

So, split personalities, parachute molecules, and swapping partners - I certainly won't be judging this element on its first appearance. That was Keele University's Pat Bailey revealing the truth about Boron. Now, next time we meet an element that also believes in humility.

Brian Clegg

When it comes to use lanthanum 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.

Meera Senthilingam

Join Brian Clegg to find out how the humble lanthanum spreads itself around town in next week's Chemistry in its Element. Until then, thank you for listening, I'm Meera Senthilingam from the Naked Scientists.com.

(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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Resources

Description :
A series of short screencasts to introduce the Chemistry of selected Elements These come from this website: http://www.chemistryvignettes.net/
Description :
A collection of visually stimulating and informative infographics about the elements, which would make a valuable addition to any science classroom.
Description :
This experiment illustrates the displacement of copper from copper(II) sulfate solution using aluminium foil
Description :
We discover how to extract lead from lead(II) oxide. We mix lead(II) oxide with charcoal powder and then heat the mixture using a Bunsen burner. It glows bright red as a reaction occurs and after a fe...
Learn Chemistry: Your single route to hundreds of free-to-access chemistry teaching resources.
 

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References

 
Visual Elements images and videos
© Murray Robertson 2011.

 

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 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.

 

Podcasts

Produced by The Naked Scientists.

 

Periodic Table of Videos

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