Periodic Table > Rubidium
 

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 Melting point 39.3 oC, 102.74 oF, 312.45 K 
Period Boiling point 688 oC, 1270.4 oF, 961.15 K 
Block Density (kg m-3) 1533 
Atomic number 37  Relative atomic mass 85.468  
State at room temperature Solid  Key isotopes 85Rb, 87Rb 
Electron configuration [Kr] 5s1  CAS number 7440-17-7 
ChemSpider ID 4512975 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
“Electric Eye” - reflects the use of Rubidium in photo-electric cells.
Appearance
A soft metal that ignites in the air and reacts violently with water. It has no biological role, but because of its chemical similarity to potassium, we absorb it from our food, and the average person has stores of about half a gram.
Uses
Rubidium is used little outside research. It is easily ionised so was considered for use in ion engines, but was found to be less effective than caesium. It has been proposed for use as a working fluid for vapour turbines and in thermoelectric generators. It is used as a photocell component and in special glasses.
Biological role
Rubidium has no known biological role and is non-toxic but because of its chemical similarity to potassium, we absorb it from our food. It is slightly radioactive and so has been used to locate brain tumours, as it collects in tumours but not in normal tissue.
Natural abundance
Rubidium is the twenty-third most abundant element in the Earth’s crust. It occurs in the minerals pollucite, carnallite, leucite and lepidolite, from which it is recovered commercially. Potassium minerals and brines also contain this element and are a further commercial source.
 
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) 3.030 Covalent radius (Å) 2.15
Electron affinity (kJ mol-1) 46.868 Electronegativity
(Pauling scale)
0.820
Ionisation energies
(kJ mol-1)
 
1st
403.031
2nd
2633.034
3rd
3859.410
4th
5075.125
5th
6850.453
6th
8143.356
7th
9571.338
8th
13121.995
 

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 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 1
Isotopes Isotope Atomic mass Natural abundance (%) Half life Mode of decay
  85Rb 84.912 72.17
  87Rb 86.909 27.83 4.88 x 1010 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)
31.06 Young's modulus (GPa) Unknown
Shear modulus (GPa) Unknown Bulk modulus (GPa) 2.5
Vapour pressure  
Temperature (K)
400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
Pressure (Pa)
0.17 - - - - - - - - - -
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History

The lithium potassium mineral lepidolite was discovered in the 1760s and it behaved oddly. When thrown on to glowing coals it frothed and then hardened like glass. Analysis showed it to contain lithium and potassium, but it held a secret: rubidium.


In 1861, Robert Bunsen and Gustav Kirchhoff, of the University of Heidelberg, dissolved the ore in acid and then precipitated the potassium it contained which carried down another heavier alkali metal. By carefully washing this precipitate with boiling water they removed the more soluble potassium component and then confirmed that they really had a new element by examining the atomic spectrum of what remained. This showed two intense ruby red lines never seen before, indicating a new element, which they named after this colour.


A sample of pure rubidium metal was eventually produced in 1928.

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Podcasts

Listen to Rubidium Podcast
Transcript :

Chemistry in Its Element - Rubidium


  (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've got a radio active element that's good at keeping time but also has some fire in its belly.   With more on the chemistry of Rubidium, here's Tom Bond. 

 

Tom Bond

 

In a way, the story of rubidium starts in 1859 when the German chemists Robert Bunsen and Gustav Kirchoff invented the spectroscope and in turn opened the door to a new age of chemical analysis. Before that the Bunsen burner had been developed to investigate the coloured flames they saw when combusting various metals and salts. Bunsen and Kirchoff were able to work out that, by using an external light source and a prism, they could separate the wavelengths of emission spectra in these flames, and so the spectroscope was born. 

 

Caesium was their first major discovery using the spectroscope, followed quickly in 1861 by rubidium, which was detected by the red flame produced when they burnt the mineral lepidolite, which contains small amounts of rubidium. Bunsen and Kirchoff realised this colour came from an unknown substance and were then able to purify a small amount of rubidium. Its name is derived from the Latin rubidus, meaning deepest red, which relates to the colour seen after excitation of the single electron in its outer shell. 

 

Rubidium is actually one of our commoner elements and   depending on which information source you look at, it is about the 16th most abundant element in the earth's crust, with a concentration somewhere around 90 parts per million. Although it is relatively abundant compared with other elements such as copper, it is not found in a pure state but as a minor fraction in various minerals. Most rubidium is derived as a by product of lepidolite extraction which has the primary goal of producing lithium. Pure rubidium is often obtained by reduction of rubidium chloride using metallic calcium at around 750 ºC and low pressures.  

 

Rubidium is one of the alkaline metals, as group one of the periodic table are otherwise known. The alkali metals have a single electron in their outer shell, which makes them highly reactive with oxygen, water and halogens, and also means that their oxidation state never exceeds +1. As you move down Group 1 of the periodic table the reactivity of the elements increases which is in line with the increasing energy of the outer electron.

 

While lithium and sodium added to water form part of school chemistry experiments, the extra reactivity of rubidium means the equivalent reaction requires caution and is not for the faint hearted. When a small amount of rubidium is chucked into water, the effect is pretty impressive, and in fact is so violent that the liberated hydrogen can ignite. Rubidium is so reactive that it can catch fire spontaneously in air, meaning it has to be stored under inert conditions. 

 

In terms of their physical properties, the elements of Group 1 are soft metals with low-melting points. Rubidium is no exception to this rule, being silvery-white and melting at 39 ºC. The element has two naturally occurring isotopes. Rubidium-85 is the dominant form, accounting for 72 per cent of the total, while most of the remainder is the radioactive rubidium-87, which has a half-life of 50 billion years. The radioactive isotope decays to form strontium-87. This process gives a way to age rocks, by measuring the isotopes of rubidium and strontium with mass spectrometry, then calculating the ratios of the radioactive forms to their decay products.

 

Although it is chemically interesting, the element has relatively few commercial applications at present, but the amount of research activity suggests many possibilities exist. One current use is in atomic clocks, though rubidium is considered less accurate than caesium. The rubidium version of the atomic clock employs the transition between two hyperfine energy states of the rubidium-87 isotope. These clocks use microwave radiation which is tuned until it matches the hyperfine transition, at which point the interval between wave crests of the radiation can be used to calibrate time itself.

 

Rubidium was chosen to investigate the unusual properties of extremely low-temperature fluids, known as Bose-Einstein condensates which have zero viscosity and the ability to spontaneously flow out of their containers. Their existence was predicted in 1925 by Einstein himself, who extended the work of Indian physicist S. N. Bose to suggest bosonic atoms at temperatures close to absolute zero would form their lowest possible energy state, which might allow quantum behaviour to be studied. By the way, bosons are defined as atoms with integer spin, while multiple bosons can occupy the same energy state. It was not until the end of the 20th century that technology advances made cooling elements close to absolute zero feasible. The first pure Bose-Einstein condensate was created using rubidium-87 by a group from the University of Colorado in the US, and for this achievement they earned the 2001 Nobel Prize for physics. 

 

Rubidium is not particularly harmful to humans, and once in the body its ions are rapidly excreted in sweat and urine. Rubidium chloride has been used to study the transport of potassium ions in humans, since rubidium ions are not naturally found in the body and when present they are treated as if they were potassium. In a similar way, because it tends to collect inside cells, especially tumours, the radioactive isotope Rb-82 can be used to locate brain tumours. 

 

The low toxicity of rubidium is confirmed by a study from 1971 which aimed to assess the feasibility of using rubidium chloride as an anti-depressant, since similar effects had been observed in monkeys. After being given 23 grams of rubidium over 75 days, a volunteer showed no harmful side effects. It does though make you wonder whether equivalent clinical studies could take place now. Meanwhile, clinical applications of rubidium in psychiatry have yet to come to fruition.    So there we have rubidium, the explosive red element number 37 in the periodic table. 

 

Meera Senthilingam

 

So this explosive element may have minimal commercial applications but can be used in atomic clocks and has isotopes that can locate brain tumours.   Not bad considering it was stumbled upon when analysing the mineral lepidolite.   That was Tom Bond with the story of rubidium.    Now next week we meet the element that's made our modern lifestyles possible.  

 

John Whitfield

 

A mixture of powdered tantalum and tantalum oxide is used in mobile phone capacitors, components that store electrical charge and control the flow of current. What makes the element ideal for phones, and for other dinky electronic gadgets, such as handheld game consoles, laptops and digital cameras, is that the metal is extremely good at conducting both heat and electricity, meaning that it can be used in small components that don't crack up under pressure. 

 

Meera Senthilingam

 

And John Whitfield will be explaining why we have tantalum to thank the next time we play the latest computer games, take hundreds of photos on holiday or when we're downloading this podcast on our laptops. So join John on next week's Chemistry in its Element.   Until then, I'm Meera Senthilingam and thank you for listening.  

 

(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

Description :
A teaching resource on The Alkali Metals supported by video clips from the Royal Institution Christmas Lectures® 2012.
Description :
A series of short, fun videos exploring the chemistry of the alkali metals, taken from a lecture by Dr. Peter Wothers at the University of Cambridge.
Description :
A series of short, fun videos exploring the chemistry of the alkali metals, taken from a lecture by Dr. Peter Wothers at the University of Cambridge.
Description :
A look at these reactive alkali metals
Description :
The fizzing reaction of rubidium with water.
Description :
A teaching resource on the Group 1 Flame tests, supported by video clips based around the Royal Institution 2012 Christmas Lectures®.
 

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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.