Erbium: the essentials

 pure erbium metal is soft and malleable and has a bright, silvery, metallic lustre. As with other rare-earth metals, its properties depend to a certain extent on impurities present. The metal is fairly stable in air and does not oxidise as rapidly as some of the other rare-earth metals.

Erbium was discovered by Carl G. Mosander at 1842 in Sweden. Origin of name: named after the village of "Ytterby" near Vaxholm in Sweden

In 1842 Gustav Mosander separated "yttria", found in the mineral gadolinite, into three fractions which he called yttria, erbia, and terbia. The names erbia and terbia became confused in this early period. After 1860, Mosander's terbia was known as erbia, and after 1877, the earlier known erbia became terbia. The erbia of this period was later shown to consist of five oxides, now known as erbia, scandia, holmia, thulia and ytterbia. Klemm and Bommer first produced reasonably pure erbium metal in 1934 by reducing the anhydrous chloride with potassium vapour.

Table: basic information about and classifications of erbium.
  • Name: Erbium
  • Symbol: Er
  • Atomic number: 68
  • Atomic weight: 167.259 (3)
  • Standard state: solid at 298 K
  • CAS Registry ID: 7440-52-0
  • Group in periodic table:
  • Group name: Lanthanoid
  • Period in periodic table: 6 (lanthanoid)
  • Block in periodic table: f-block
  • Colour: silvery white
  • Classification: Metallic

erbium
This sample is from The Elements Collection, an attractive and safely packaged collection of the 92 naturally occurring elements that is available for sale.

Isolation

erbium metal is available commercially so it is not normally necessary to make it in the laboratory, which is just as well as it is difficult to isolate as the pure metal. This is largely because of the way it is found in nature. The lanthanoids are found in nature in a number of minerals. The most important are xenotime, monazite, and bastnaesite. The first two are orthophosphate minerals LnPO4 (Ln deonotes a mixture of all the lanthanoids except promethium which is vanishingly rare) and the third is a fluoride carbonate LnCO3F. Lanthanoids with even atomic numbers are more common. The most comon lanthanoids in these minerals are, in order, cerium, lanthanum, neodymium, and praseodymium. Monazite also contains thorium and ytrrium which makes handling difficult since thorium and its decomposition products are radioactive.

For many purposes it is not particularly necessary to separate the metals, but if separation into individual metals is required, the process is complex. Initially, the metals are extracted as salts from the ores by extraction with sulphuric acid (H2SO4), hydrochloric acid (HCl), and sodium hydroxide (NaOH). Modern purification techniques for these lanthanoid salt mixtures are ingenious and involve selective complexation techniques, solvent extractions, and ion exchange chromatography.

Pure erbium is available through the reduction of ErF3 with calcium metal.

2ErF3 + 3Ca → 2Er + 3CaF2

This would work for the other calcium halides as well but the product CaF2 is easier to handle under the reaction conditions (heat to 50°C above the melting point of the element in an argon atmosphere). Excess calcium is removed from the reaction mixture under vacuum.

Neutral radii

The size of neutral atoms depends upon the way in which the measurement is made and the environment. Follow the appropriate hyperlinks for definitions of each radius type. The term "atomic radius" is not particularly helpful although its use is widespread. The problem is its meaning, which is clearly very different in different sources and books. Two values are given here, one is based upon calculations and the other upon observation - follow the appropriate link for further details.

  • Atomic radius (empirical): 175  pm
  • Atomic radius (calculated): 226  pm
  • Covalent radius (2008 values): 189  pm

Ionic radii

This table gives some ionic radii. In this table, geometry refers to the arrangment of the ion's nearest neighbours. Size does depend upon geometry and environment. For electronic configurations, where it matters, the values given for octahedral species are low spin unless stated to be high spin. The terms low spin and high spin refer to the electronic configurations of particular geomtries of certain d-block metal ions. Further information is available in inorganic chemistry textbooks, usually at Level 1 or First Year University level. For definitions of ionic radius and further information, follow the hypertext link.

Ion Coordination type Radius / pm
Er(III) 6-coordinate, octahedral 103.0
Er(III) 8-coordinate 114.4

The electron affinity of erbium is 50  kJ mol-1.

Ionisation Energies

This section includes ionisation energies of erbium.

Ionisation energy number Enthalpy /kJ mol-1
1st 589.3
2nd 1150
3rd 2194
4th 4120

Electronic configuration

The following represents the electronic configuration and its associated term symbol for the ground state neutral gaseous atom. The configuration associated with erbium in its compounds is not necessarily the same.

  • Ground state electron configuration:  [Xe].4f12.6s2
  • Shell structure:  2.8.18.30.8.2
  • Term symbol:   3H6

Reaction of erbium with air

Erbium metal tarnishes slowly in air and burns readily to form erbium (III) oxide, Er2O3.

4Er + 3O2 → 2Er2O3

Reaction of erbium with water

The silvery white metal erbium is quite electropositive and reacts slowly with cold water and quite quickly with hot water to form erbium hydroxide, Er(OH)3, and hydrogen gas (H2).

2Er(s) + 6H2O(g) → 2Er(OH)3(aq) + 3H2(g)

Reaction of erbium with the halogens

Erbium metal reacts with all the halogens to form erbium(III) halides. So, it reacts with fluorine, F2, chlorine, Cl2, bromine, I2, and iodine, I2, to form respectively erbium(III) bromide, ErF3, erbium(III) chloride, ErCl3, erbium(III) bromide, ErBr3, and erbium(III) iodide, ErI3.

2Er(s) + 3F2(g) → 2ErF3(s) [pink]

2Er(s) + 3Cl2(g) → 2ErCl3(s) [violet]

2Er(s) + 3Br2(g) → 2ErBr3(s) [violet]

2Er(s) + 3I2(g) → 2ErI3(s) [violet]

Reaction of erbium with acids

Erbium metal dissolves readily in dilute sulphuric acid to form solutions containing the yellow aquated Er(III) ion together with hydrogen gas, H2. It is quite likely that Er3+(aq) exists as largely the complex ion [Er(OH2)9]3+

2Er(s) + 3H2SO4(aq) → 2Er3+(aq) + 3SO42-(aq) + 3H2(g)

Here is some information about the crystal structure of erbium.

  • Space group: P63/mmc (Space group number: 194)
  • Structure: hcp (hexagonal close-packed)
  • Cell parameters:
    • a: 355.88 pm
    • b: 355.88 pm
    • c: 558.74 pm
    • α: 90.000°
    • β: 90.000°
    • γ: 120.000°

The most used definition of electronegativity is that an element's electronegativity is the power of an atom when in a molecule to attract electron density to itself. The electronegativity depends upon a number of factors and in particuler as the other atoms in the molecule. The first scale of electronegativity was developed by Linus Pauling and on his scale erbium has a value of 1.24 on a scale running from from about 0.7 (an estimate for francium) to 2.20 (for hydrogen) to 3.98 (fluorine). Electronegativity has no units but "Pauling units" are often used when indicating values mapped on to the Pauling scale. On the interactive plot below you may find the "Ball chart" and "Shaded table" styles most useful.

Table of Different types of electronegativity for erbium. Use the links in the "Electronegativity" column for definitions, literature sources, and visual representations in many different styles (one of which is shown below). All values are quoted on the Pauling scale.
Electronegativity Value in Pauling units
Pauling electronegativity 1.24
Sanderson electronegativity no data
Allred Rochow electronegativity 1.11

Erbium is never found in nature as the free element. Erbium is found in the ores monazite sand [(Ce, La, etc.)PO4] and bastn°site [(Ce, La, etc.)(CO3)F], ores containing small amounts of all the rare earth metals. It is difficult to separate from other rare earth elements.

Abundances of erbium in various environments

In this table of abundances, values are given in units of ppb (parts per billion; 1 billion = 109), both in terms of weight and in terms of numbers of atoms. Values for abundances are difficult to determine with certainty, so all values should be treated with some caution, especially so for the less common elements. Local concentrations of any element can vary from those given here an orders of magnitude or so and values in various literature sources for less common elements do seem to vary considerably.

Abundances for erbium in a number of different environments. Use the links in the location column for definitions, literature sources, and visual representations in many different styles (one of which is shown below)
Location ppb by weight ppb by atoms
Universe 2 0.01
Sun 1 0.01
Meteorite (carbonaceous) 180 20
Crustal rocks 3000 370
Sea water 0.0009 0.000033
Stream 0.05 0.0003

Erbium has six stable isotopes but only Er-168 appears to have a well established application. Er-168 is used for the production of Er-169 which is used in form of citrate for the treatment of rheumatoid arthritis. Erbium isotopes can be obtained from Trace Sciences International.

Naturally occurring isotopes

Isotope Atomic mass (ma/u) Natural abundance (atom %) Nuclear spin (I) Magnetic moment (μ/μN)
162Er 161.928775 (4) 0.14 (1) 0
164Er 163.929198 (4) 1.61 (3) 0
166Er 165.930290 (4) 33.61 (35) 0
167Er 166.932046 (4) 22.93 (17) 7/2 -0.5665
168Er 167.932368 (4) 26.78 (26) 0
170Er 169.935461 (4) 14.93 (27) 0

Radiosotope data

Isotope Mass Half-life Mode of decay Nuclear spin Nuclear magnetic moment
160Er 159.92908 1.19 d EC to 160Ho 0
161Er 160.9300 3.21 h EC to 161Ho 3/2 -0.37
163Er 162.93003 1.25 h EC to 163Ho 5/2 0.557
165Er 164.930723 10.36 h EC to 165Ho 5/2 0.643
169Er 168.934588 9.40 d β- to 169Tm 1/2 0.515
171Er 170.938026 7.52 h β- to 171Tm 5/2 0.66
172Er 171.939352 2.05 d β- to 172Tm

Chlorides

  • ErCl3:
    thermochemical cycle: (no value) kJ mol-1
    calculated: 4527 kJ mol-1

Oxides

  • Er2O3:
    thermochemical cycle: (no value) kJ mol-1
    calculated: 13263 kJ mol-1

Common reference compound: .

Table of NMR-active nucleus propeties of erbium
  Isotope 1 Isotope 2 Isotope 3
Isotope 167Er
Natural abundance /% 22.95
Spin (I) 7/2
Frequency relative to 1H = 100 (MHz) about 2.88
Receptivity, DP, relative to 1H = 1.00 -
Receptivity, DC, relative to 13C = 1.00 -
Magnetogyric ratio, γ (107 rad T-1 s-1) -0.77157
Magnetic moment, μ (μN) -0.63935
Nuclear quadrupole moment, Q (barn) 3.57
Line width factor, 1056l (m4)

Valence shell orbital radii

The following are calculated values of valence shell orbital radii, Rmax

Table: valence shell orbital radii for erbium.
Orbital Radius [/pm] Radius [/AU]
s orbital 203.1 3.83742
f orbital 26.8 0.505998

Effective Nuclear Charges

The following are "Clementi-Raimondi" effective nuclear charges, Zeff. Follow the hyperlinks for more details and for graphs in various formats.

Table: effective nuclear charges for erbium
1s 66.67  
2s 50.20 2p 63.65  
3s 47.08 3p 47.61 3d 54.36  
4s 36.23 4p 35.11 4d 32.27 4f 27.98
5s 19.72 5p 17.47 5d no data  
6s 8.48

Electron binding energies

This table contains electron binding energies for erbium.
Label Orbital eV [literature reference]
K 1s 57486 [1]
L I 2s 9751 [1]
L II 2p1/2 9264 [1]
L III 2p3/2 8358 [1]
M I 3s 2206 [1]
M II 3p1/2 2006 [1]
M III 3p3/2 1812 [1]
M IV 3d3/2 1453 [1]
M V 3d5/2 1409 [1]
N I 4s 449.8 [2]
N II 4p1/2 366.2 [1]
N III 4p3/2 320.2 [2]
N IV 4d3/2 167.6 [2]
N V 4d5/2 167.6 [2]
N VI 4f5/2 -
N VII 4f7/2 4.7 [2]
O I 5s 50.6 [2]
O II 5p1/2 31.4 [2]
O III 5p3/2 24.7 [2]

Temperatures

  • Melting point: 1770 [or 1497 °C (2727 °F)] K
  • Boiling point: 3141 [or 2868 °C (5194 °F)] K (liquid range: 1371  K

Expansion and conduction properties

  • Thermal conductivity: 15  W m-1 K-1
  • Coefficient of linear thermal expansion: 12.2  x 10-6 K-1

Bulk properties

  • Density of solid: 9066  kg m-3
  • Molar volume: 18.46  cm3
  • Velocity of sound: 2830  m s-1

Elastic properties

  • Youngs modulus: 70  GPa
  • Rigidity modulus: 28  GPa
  • Bulk modulus: 44  GPa
  • Poissons ratio: 0.24  (no units)

Hardnesses

  • Brinell hardness: 814  MN m-2
  • Vickers hardness: 589  MN m-2

Electrical properties

  • Electrical resistivity: 86  10-8 Ω m; or mΩ cm

Enthalpies

  • Enthalpy of fusion: 19.9  kJ mol-1
  • Enthalpy of vaporisation: 285  kJ mol-1
  • Enthalpy of atomisation: 317  kJ mol-1

Thermodynamic data

Table: thermodynamic data for erbium.
State ΔfH° ΔfG° S° CpH H°298.15-H°0
Units kJ mol-1 kJ mol-1 J K-1 mol-1 J K-1 mol-1 kJ mol-1
Solid 0 0 73.2 28.1 7.38
Gas 317 281 195.5 20.8 6.2

The following uses for erbium are gathered from a number of sources as well as from anecdotal comments. I'd be delighted to receive corrections as well as additional referenced uses (please use the feedback mechanism to add uses).

  • nuclear industry
  • metallurgical uses. Added to vanadium, for example, erbium lowers hardness and improves workability
  • erbium oxide is pink and is a colourant in glasses and porcelain enamel glazes
  • photographic filter