57
  La  
138.905500
Lanthanum

Name: Lanthanum
Symbol: La
Atomic Number: 57
Atomic Weight: 138.905500
Family: Rare Earth Elements
CAS RN: 7439-91-0
Description: A silvery white, malleable, ductile, and soft rare-earth metal.
State (25 C): Solid
Oxidation states: +3

Molar Volume: 22.6 cm3/mole
Valence Electrons: 5d16s2

Boiling Point:  3730K, 3457C, 6255F
Melting Point:
1193K, 920C, 1688F
Electrons Energy Level: 2, 8, 18, 18, 9, 2
Isotopes: 38 + 1 Stable
Heat of Vaporization: 414 kJ/mol
Heat of Fusion: 6.2 kJ/mol
Density: 6.15 g/cm3 @ 300K
Specific Heat: 0.19 J/gK
Atomic Radius: 2.74
Ionic Radius: 1.061
Electronegativity: 1.1 (Pauling); 1.08 (Allrod Rochow)
Vapor Pressure: 1.33 E-07 Pa @ 920C
57
La
138.9
58
Ce
140.1
59
Pr
140.9
60
Nd
144.2
61
Pm
(145)
62
Sm
150.4
63
Eu
152.0
64
Gd
157.3
65
Tb
158.9
66
Dy
162.5
67
Ho
164.9
68
Er
167.3
69
Tm
168.9
70
Yb
173.0
71
Lu
175.0

1s2 2s2p6 3s2p6d10 4s2p6d10 5s2p6d1 6s2

History

Lanthanum was discovered in 1839 by Swedish chemist Carl Gustav Mosander, when he partially decomposed a sample of cerium nitrate by heating and treating the resulting salt with dilute nitric acid.  From the resulting solution, he isolated a new rare earth he called lantana. Lanthanum was isolated in relatively pure form in 1923.

The word lanthanum comes from the Greek, lanthanein, "to lie hidden".  That is an apt description since lanthanum generally occurs along with other so-called rare earth elements and is very difficult to separate. The abundance of the metal is similar to that of zinc or nickel.

Characteristics

Lanthanum is a silvery white metallic element belonging to group 3 of the periodic table and often considered to be one of the lanthanides.  Found in some rare-earth minerals, usually in combination with cerium and other rare earth elements.   Lanthanum is malleable, ductile, and soft enough to be cut with a knife.  It is one of the most reactive of the rare-earth metals.  The metal reacts directly with elemental carbon, nitrogen, boron, selenium, silicon, phosphorus, sulfur, and with halogens.  It oxidizes rapidly when exposed to air. Cold water attacks lanthanum slowly, while hot water attacks it much more rapidly.

1s2
2s2 2p6
3s2 3p6 3d10
4s2 4p6 4d10
5s2 5p6 5d1
6s2

For that reason the metal is usually stored under oil or kerosene. Most lanthanum is extracted from monazite sands.  Lanthanum is used in the electrodes for high-intensity carbon-arc lamps and also in the production of high-purity europium metal (element 63). 

Occurrence

Although lanthanum belongs to chemical elements group called rare earth metals, it is not rare at all.  Lanthanum is available in relatively large quantities (32 ppm in Earth’s crust).

Monazite (Ce, La, Th, Nd, Y)PO4, and bastnasite (Ce, La, Y)CO3F, are principal ores in which lanthanum occurs in percentages up to 25 to 38 percent.

Applications

Lanthanum has no known biological role.  The element is not absorbed orally, and when injected its elimination is very slow. Lanthanum carbonate was approved as a medication (Fosrenol, Shire Pharmaceuticals) to absorb excess phosphate in cases of end-stage renal failure. Some rare-earth chlorides, such as lanthanum chloride (LaCl3), are known to have anticoagulant properties.

While Lanthanum has pharmacological effects on several receptors and ion channels its specificity for the GABA receptor is unique among divalent cations. Lanthanum acts at the same modulatory site on the GABAR as zinc- a known negative allosteric modulator. The Lanthanum cation La3+ is a positive allosteric modulator at native and recombinant GABA receptors, increasing open channel time and decreasing desensitization in a subunit configuration dependent manner.

Compounds

Monazite, (Ce, La, Th, Nd, Y)PO4 Bastnasite, (Ce, La, Y)CO3F
Lanthana, Lanthanum Oxide, La2O3 Lanthanum Boride, LaB6

Isotope

Naturally occurring lanthanum is composed of one stable (139La) and one radioactive (138La) isotope, with the stable isotope, 139La, being the most abundant (99.91% natural abundance.  38 radioisotopes have been characterized with the most stable being 138La with a half-life of 105109 years, and 137La with a half-life of 60,000 years. All of the remaining radioactive isotopes have half-lives that are less than 24 hours and the majority of these have half lives that are less than 1 minute. This element also has 3 meta states.

The isotopes of lanthanum range in atomic weight from 117 u (117La) to 155 u (155La).

atom.gif (700 bytes)

Isotope Atomic Mass Half-Life
La117 116.95 23.5 ms
La118 117.947 ˜ 1 seconds
La119 118.941 ˜ 2 seconds
La120 119.938 2.8 seconds
La121 120.933 5.3 seconds
La122 121.931 8.7 seconds
La123 122.926 17 seconds
La124 123.925 29 seconds
La125 124.921 76 seconds
La126 125.919 54 seconds
La127 126.916 5.1 minutes
La128 127.915 5 minutes
La129 128.9127 11.6 minutes
La130 129.912 8.7 minutes
La131 130.91 59 minutes
La132 131.9101 4.8 hours
La133 132.908 3.912 hours
La134 133.9085 6.45 minutes
La135 134.907 19.5 hours
La136 135.9077 9.87 minutes
La137 136.9065 60,000 years
La138 137.9071 1.05E 11 years
La139 138.9064 Stable
La140 139.9095 1.6781days
La141 140.911 3.92 hours
La142 141.9141 91.1 minutes
La143 142.9161 14.2 minutes
La144 143.9196 40.8 seconds
La145 144.9216 24.8 seconds
La146 145.9257 6.27 seconds
La147 146.9278 4.015 seconds
La148 147.932 1.05 seconds
La149 148.934 1.05 seconds
La150 149.939 0.86 seconds
La151 150.942 > 150 ns
La152 151.946 >150 ns
La153 152.949 >150 ns
La154 153.954 ˜ 0.1 seconds
La155 154.958 ˜ 0.06 seconds

Precautions

40px-Skull_and_crossbones.svg.jpg (1420 bytes) Lanthanum has a low to moderate level of toxicity, and should be handled with care.  In animals, the injection of lanthanum solutions produces glycaemia, low blood pressure, degeneration of the spleen and hepatic alterations.

atom.gif (700 bytes)

Lanthanum Data
 

Atomic Structure

  • Atomic Radius: 2.74
  • Atomic Volume: 20.73cm3/mol
  • Covalent Radius: 1.69
  • Cross Section (Thermal Neutron Capture) Barns: 8.98
  • Crystal Structure: Hexagonal
  • Electron Configuration:
    1s2 2s2p6 3s2p6d10 4s2p6d10 5s2p6d1 6s2
  • Electrons per Energy Level: 2, 8, 18, 18, 9, 2
  • Ionic Radius: 1.061
  • Filling Orbital: 5d1
  • Number of Electrons (with no charge): 57
  • Number of Neutrons (most common/stable nuclide): 82
  • Number of Protons: 57
  • Oxidation States: 3
  • Valence Electrons: 5p1 6s2

Chemical Properties

  • Electrochemical Equivalents: 1.7275 g/amp-hr
  • Electron Work Function: 3.5eV
  • Electronegativity: 1.1 (Pauling); 1.08 (Allrod Rochow)
  • Heat of Fusion: 6.2 kJ/mol
  • Incompatibilities:
  • Ionization Potential
    • First: 5.58
    • Second: 11.059
    • Third: 19.174
  • Valence Electron Potential (-eV): 40.71

Physical Properties

  • Atomic Mass Average: 138.9055
  • Boiling Point: 3730K, 3457C, 6255F
  • Coefficient of Lineal Thermal Expansion/K-1: 4.9E-6
  • Conductivity
    Electrical: 0.0126 106/cm
    Thermal: 0.135 W/cmK
  • Density: 6.15 g/cm3 @ 300K
  • Description:
    Soft silvery white transition (rare earth) metal that rapidly tarnishes in air. It will burn easily if ignited.
  • Elastic Modulus:
    • Bulk: 28/GPa
    • Rigidity: 14.9/GPa
    • Youngs: 37.9/GPa
  • Enthalpy of Atomization: 431 kJ/mole @ 25C
  • Enthalpy of Fusion: 6.2 kJ/mole
  • Enthalpy of Vaporization: 399.6 kJ/mole
  • Flammablity Class:
  • Freezing Point: see melting point
  • Hardness Scale
    • Brinell: 363 MN m-2
    • Mohs: 2.5
    • Vickers: 491 MN m-2
  • Heat of Vaporization: 414 kJ/mol
  • Melting Point: 1193K, 920C, 1688F
  • Molar Volume: 22.6 cm3/mole
  • Physical State (at 20C & 1atm): Solid
  • Specific Heat: 0.19 J/gK
  • Vapor Pressure: 1.33 E-07 Pa @ 920C

Regulatory / Health

  • CAS Number
    • 7439-91-0
  • OSHA Permissible Exposure Limit (PEL)
    • No limits set by OSHA
  • OSHA PEL Vacated 1989
    • No limits set by OSHA
  • NIOSH Recommended Exposure Limit (REL)
    • No limits set by NIOSH
  • Levels In Humans:
    Note: this data represents naturally occuring levels of elements in the typical human, it DOES NOT represent recommended daily allowances.
    • Blood/mg dm-3: n/a
    • Bone/p.p.m: <0.08
    • Liver/p.p.m: 0.3
    • Muscle/p.p.m: 0.0004
    • Daily Dietary Intake: n/a
    • Total Mass In Avg. 70kg human: 0.8 mg
  • Discovery Year: 1839
  • Name Origin:
    Greek: lanthanein (to lie hidden).
  • Abundance:
    • Earth's Crust/p.p.m.: 32
    • Seawater/p.p.m.:
      • Atlantic Suface: 0.0000018
      • Atlantic Deep: 0.0000038
      • Pacific Surface: 0.0000026
      • Pacific Deep: 0.0000069
    • Atmosphere/p.p.m.: N/A
    • Sun (Relative to H=1E12): 13.5
  • Sources:
    Found with rare earths in monazite and bastnasite. Around 12,500 tons are produced world wide each year. Primary mining areas are USA, Brazil, India, Sri Lanka, Australia.
  • Uses:
    Because it gives glass refractive properties, it is used in expensive camera lenses. Also used in lighter flints, battery electrodes and catalytic converters.

Ionization Energy (eV): 5.577 eV
Estimated Crustal Abundance: 3.9101 milligrams per kilogram
Estimated Oceanic Abundance:
3.410-6 milligrams per liter

Transition Metals
Group 3
(IIIB)
4
(IVB)
5
(VB)
6
(VIB)
7
(VIIB)
8
(VIIIB)
9
(VIIIB)
10 (VIIIB) 11
(IB)
12
(IIB)
Period 4 21
Sc
44.95
22
Ti
47.86
23
V
50.94
24
Cr
51.99
25
Mn
54.93
26
Fe
55.84
27
Co
58.93
28
Ni
58.69
29
Cu
63.54
30
Zn
65.39
Period 5 39
Y
88.90
40
Zr
91.22
41
Nb
92.90
42
Mo
95.94
43
Tc
98.00
44
Ru
101.0
45
Rh
102.9
46
Pd
106.4
47
Ag
107.8
48
Cd
112.4
Period 6 57
La
138.9
72
Hf
178.4
73
Ta
180.9
74
W
183.8
75
Re
186.2
76
Os
190.2
77
Ir
192.2
78
Pt
195.0
79
Au
196.9
80
Hg
200.5
Period 7 89
Ac
227.0
104
Rf
261.0
105
Db
262.0
106
Sg
266.0
107
Bh
264.0
108
Hs
269.0
109
Mt
268.0
110
Ds
269.0
111
Rg
272.0
112
Uub
277.0

(Gr. lanthanein, to lie hidden) Mosander in 1839 extracted a new earth lanthana, from impure cerium nitrate and recognized the new element. Lanthanum is found in rare-earth minerals such as cerite, monazite, allanite, and bastnasite. Monazite and bastnasite are principal ores in which lanthanum occurs in percentages up to 25 and 38% respectively. Misch metal, used in making lighter flints, contains about 25% lanthanum. Lanthanum was isolated in relatively pure form in 1923, iron exchange and solvent extraction techniques have led to much easier isolation of the so-called "rare-earth" elements. The availability of lanthanum and other rare earths has improved greatly in recent years. the metal can be produced by reducing the anhydrous fluoride with calcium. Lanthanum is silvery white, malleable, ductile, and soft enough to be cut with a knife. It is one of the most reactive of the rare-earth metals. It oxidizes rapidly when exposed to air. Cold water attacks lanthanum slowly, and hot water attacks it much more rapidly. the metal reacts directly with elemental carbon, nitrogen, boron, selenium, silicon, phosphorus, sulfur, and with halogens. At 310oC, lanthanum changes from a hexagonal to a face-centered cubic structure, and at 865oC it again transforms into a body-centered cubic structure. Natural lanthanum is a mixture of two stable isotopes, 138La and 139La. Twenty three other radioactive isotopes are recognized. Rare-earth compounds containing lanthanum are extensively used in carbon lighting applications, especially by the motion picture industry for studio lighting and projection. This application consumes about 25% of the rare-earth compounds produced. La2O3 improves the alkali resistance of glass, and is used in making special optical glasses. Small amounts of lanthanum, as an additive, can be used to produce nodular cast iron. There is current interest in hydrogen sponge alloys containing lanthanum. These alloys take up to 400 times their own volume of hydrogen gas, and the process is reversible. Heat energy is released every time that they do so; therefore these alloys have possibilities in energy conservation system. Lanthanum and its compounds have a low to moderate acute toxicity rating; therefore, care should be taken in handling them. The metal costs about $5/g.

Source: CRC Handbook of Chemistry and Physics, 1913-1995. David R. Lide, Editor in Chief. Author: C.R. Hammond