Periodic Table > Gallium
 

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 13  Melting point 29.765 oC, 85.576 oF, 302.915 K 
Period Boiling point 2229 oC, 4044.2 oF, 2502.15 K 
Block Density (kg m-3) 5905 
Atomic number 31  Relative atomic mass 69.723  
State at room temperature Solid  Key isotopes 69Ga 
Electron configuration [Ar] 3d104s24p1  CAS number 7440-55-3 
ChemSpider ID 4514603 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 reflects on puns relating to the origin of the element’s name. Lecoq de Boisbaudran named the element after France (‘Gaul’ in Latin) and also himself, since Lecoq, which means ‘the rooster’ translates to ‘Gallus’ in Latin. A silvery metallic rooster is shown on a background of an antique map of France.

Appearance

Gallium is a soft, silvery-white metal, similar to aluminium.

Uses

Gallium arsenide has a similar structure to silicon and is a useful silicon substitute for the electronics industry. It is an important component of many semiconductors. It is also used in red LEDs (light emitting diodes) because of its ability to convert electricity to light. Solar panels on the Mars Exploration Rover contained gallium arsenide.

Gallium nitride is also a semiconductor. It has particular properties that make it very versatile. It has important uses in Blu-ray technology, mobile phones, blue and green LEDs and pressure sensors for touch switches.

Gallium readily alloys with most metals. It is particularly used in low-melting alloys.

It has a high boiling point, which makes it ideal for recording temperatures that would vaporise a thermometer.

Biological role
Gallium has no known biological role. It is non-toxic.
Natural abundance

It is present in trace amounts in the minerals diaspore, sphalerite, germanite, bauxite and coal. It is mainly produced as a by-product of zinc refining.

The metal can be obtained by electrolysis of a solution of gallium(III) hydroxide in potassium hydroxide.

 
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) 1.870 Covalent radius (Å) 1.23
Electron affinity (kJ mol-1) 41.474 Electronegativity
(Pauling scale)
1.810
Ionisation energies
(kJ mol-1)
 
1st
578.844
2nd
1979.410
3rd
2964.587
4th
6101.824
5th
8298.697
6th
10873.888
7th
13594.773
8th
16392.845
 

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 4.5
Country with largest reserve base n/a
Crustal abundance (ppm) 16
Leading producer China
Reserve base distribution (%) n/a
Production concentration (%) 32.00
Total governance factor(production) 5
Top 3 countries (mined)
  • 1) n/a
Top 3 countries (production)
  • 1) China
  • 2) Germany
  • 3) Kazakhstan
 

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 3
Isotopes Isotope Atomic mass Natural abundance (%) Half life Mode of decay
  69Ga 68.926 60.108
  71Ga 70.925 39.892 > 2.4 x 1026 β- 
 

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)
26.03 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)
- - 1.94
x 10-7
5.65
x 10-4
0.11 4.98 84.4 - - - -
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History

Gallium was discovered in Paris by Paul-Émile Lecoq de Boisbaudran in 1875. He observed a new violet line in the atomic spectrum of some zinc he had extracted from a sample of zinc blende ore (ZnS) from the Pyrenees. He knew it meant that an unknown element was present.


What Boisbaudran didn’t realise was that its existence, and properties, had been predicted by Mendeleev whose periodic table showed there was a gap below aluminium which was yet to be occupied. He forecast that the missing element’s atomic weight would be around 68 and its density would be 5.9 g/cm3.


By November of 1875, Boisbaudran had isolated and purified the new metal and shown that it was like aluminium. In December 1875 he announced it to the French Academy of Sciences.

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Podcasts

Listen to Gallium Podcast
Transcript :

Chemistry in its Element - Gallium


(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)

 

Chris Smith

Hello and this week to the story of the element that's named after a rooster although the man here to tell us about it actually chickened out when it came to eating some of this chemical, although he did confess to giving it a quick lick. And to tell us how it tasted and why Gallium could hold the key to the next generation of LEDs, here's Andrea Sella. 

 

Andrea Sella

When I was a child growing up in New York, some of the sweets most sort after by my classmates and me, with yellow and brown packs of highly coloured sugar coated chocolate pills bearing the characters M & M. You could pop them into your mouth one by one and suck them gently until the smooth surface became crumbling to reveal the smooth milk chocolate beneath; alternatively you cold cram your mouth with as many as you could and crunch them greedily to cause an explosion of sound, texture and flavour in your head. A secret pleasure that was hard to beat. I was reminded of all this when a colleague of mine who was having a lab clear out, knocked on my door and asked me knowing full well what my answer would be, 'Hi Andrea, would you like a lump of Gallium?', 'of course I would love some Gallium', I gurgled. The M & M of the elements; the one which reputedly melts in your mouth but not in your hand, he handed me a small plastic bag badly stained with black smudges. I undid the knot eagerly and there it was, a gleaming silvery lump bearing all the hallmarks of a metal that had been repeatedly melted and then refrozen.

 

Gallium, you see, melts at 30oC, which means that on a hot day, you hold it in your pocket at your peril. Surprisingly however it's not very volatile. In fact Gallium has the largest liquid range of any material known to man. Its boiling point is just over 2400oC. So unlike other liquid metals, there is no toxic vapour to worry about. Bizarrely as well, the metal contracts as it melts, rather like water. So solid Gallium floats on its liquid, a property shared only by a couple of other elements, Bismuth and Antimony.   The reason for this weird melting behaviour has been a matter of argument and speculation for about 50 years. It's now fairly well established that Gallium surrounds itself with more of its neighbours when in the liquid than in the solid, although the reasons for this still remains obscure. Yet for all its strangeness the discovery of this odd element was no accident. Dmitri Mendeleev, the bearded Russian chemist who constructed the periodic table as we know it today, spotted a number of gaps and discrepancies in his arrangement. One of these was the absence of an element which he expected to fit below Aluminum. So confident was he in the correctness of his framework that he named the as yet undiscovered element ekaaluminium. Six years later in 1875, an ambitious French element hunter François Lecoq de Boisbaudran one of the earliest proponents of the new-fangled technique of spectroscopy spotted a line in the violet part of the visible spectrum at 417nm in a sample of Zinc Sulphide, he realized that this must come from a new element. Working in his home laboratory in spite of starting from some 52 kilos of an ore from the Pyrenees, it took three weeks for him to accumulate a couple of milligrams of the mysterious material. He then scaled up his extraction and took the product of his labours to Paris where he studied it further in Adolphe Wurtz's lab. Just before Christmas in 1875, Lecoq presented his results to the French academy proudly displaying a sample of almost 600mg, less than a gram of material harvested from 450 kilos of ore. And the name Lecoq patriotically chose to base it on the Latin name for France, GalliaGaul in English. But it was immediately pointed out that there might be something more to the name than met the eye. The Latin word for a rooster is Gallus, Lecoq, rooster, Gallium, get it. It seems he may have been a rather cunning linguist as well as a chemist. Either way, Lecoq could look back with some satisfaction at having helped to cement Mendeleev's table, was the foundation stone of chemistry.   He then moved on to the intriguing mystery of the 'rare earths', ultimately isolating two more elements and conforming the existence of several more.

 

Gallium soon moved into the main stream of chemistry. Nowadays the metal itself finds few uses, but its compound with Arsenic, Gallium Arsenide has for several years been touted as a possible replacement for Silicon.   Since not only is it a semiconductor but it is one with a direct band gap, in other words it can be made into a metalloid, a property which is particularly useful for infrared but also visible LEDs. Gallium Arsenide solar cells are also much more efficient than those made of conventional Silicon and are being used in solar powered cars and in space probes. 

 

But I'm sure you really want to know is, if this really is the M & M element, what does it taste like? I knew you would ask. So I had a quick lick a couple of days back and the answer is it doesn't actually taste very much to be honest. There's a faintly astringent, metallic taste which lingers on your tongue for few hours.   And when it is molten, sorry I'll leave that experiment for someone more intrepid than I.

 

Chris Smith

UCL chemist Andrea Sella with the story of Gallium, the element that Lecoq allegedly named after himself. Next week we are meeting the metal that powers nuclear rectors but can also be lethal for another reason. 

 

Polly Arnold 

Because it is so dense DU is also used in shielding in the keels of boats and more controversially in the noses of armour piercing weapons. The metal has the desirable ability to self sharpen as it pierces a target rather than mushrooming upon impact, the way conventional tungsten carbide tipped weapons do.

 

Chris Smith

DU being Depleted Uranium of course and Edinburgh chemist Polly Arnold will be here to tell us its story as well as revealing why it actually makes very beautiful glass on next week's Chemistry in its element. I hope you can join us. I'm Chris Smith, thank you   for listening and good bye.

 

(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 element. 

 

(End promo)

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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.