Erbium
Erbium is a chemical element with the atomic number 68 and the symbol Er. It is a soft, malleable, silvery metal in the lanthanide series of the periodic table, classified as a rare earth element, and occurs naturally as a mixture of six stable isotopes.[1] Erbium was discovered in 1843 by Swedish chemist Carl Gustav Mosander while analyzing a sample of yttrium from the Ytterby mine near Stockholm, Sweden; he isolated it as a rose-colored oxide called erbia, distinguishing it from terbia (now terbium oxide).[1] The name "erbium" derives from Ytterby, the site of several rare earth discoveries.[2] Erbium ranks as the 43rd most abundant element in Earth's crust, with an estimated concentration of about 3.5 parts per million, primarily found in minerals such as monazite, xenotime, and bastnäsite.[3] Physically, erbium has a density of 9.07 g/cm³, a melting point of 1529 °C, and a boiling point of 2868 °C; it is paramagnetic at room temperature and exhibits a metallic luster that tarnishes in air due to oxidation.[2] Chemically, it is reactive, dissolving readily in dilute acids to release hydrogen gas, and forms compounds primarily in the +3 oxidation state, such as erbium oxide (Er₂O₃), which is stable and pink in color.[4] Erbium's most prominent applications stem from its optical properties, particularly its ability to amplify signals in the infrared spectrum; it is doped into fiber-optic cables to create erbium-doped fiber amplifiers (EDFAs), essential for long-distance telecommunications and the internet backbone.[2] In metallurgy, erbium is alloyed with vanadium to improve workability and reduce hardness, and its oxide is used to impart a pink tint to glass and porcelain.[5] Additional uses include nuclear reactors as a neutron absorber in control rods[6], medical lasers for skin resurfacing and tissue ablation[7], and emerging roles in quantum communication devices due to erbium ions' telecom-compatible emission wavelengths.[8]Properties
Physical properties
Erbium (Er) is element 68 in the periodic table, with an atomic mass of 167.259 u and an electron configuration of [Xe] 4f^{12} 6s^2.[2][9] This configuration places it among the lanthanides, contributing to its characteristic metallic properties. In its pure form, erbium appears as a soft, malleable, silvery-white metal that slowly tarnishes in air due to surface oxidation.[9][10] The metal exhibits a density of 9.066 g/cm³ at 20°C and a specific heat capacity of 168 J/kg·K, reflecting its capacity to store thermal energy efficiently compared to many transition metals.[11] Erbium melts at 1529 °C and boils at 2868 °C, indicating high thermal stability suitable for applications requiring elevated temperatures.[2] Its electrical resistivity measures 0.86 µΩ·m at room temperature, consistent with moderate conductivity typical of rare-earth metals.[11] The metal is paramagnetic, with a magnetic susceptibility \chi = 11.4 \times 10^{-6} cm³/mol at 20°C, arising from unpaired electrons in its 4f orbitals.[12] Structurally, erbium adopts a hexagonal close-packed (hcp) crystal lattice, with parameters a = 0.3559 nm and c = 0.5587 nm, which influences its mechanical ductility and thermal expansion behavior.Chemical properties
Erbium, as a member of the lanthanide series, predominantly displays the +3 oxidation state (Er³⁺) in its chemical compounds, reflecting the typical behavior of rare earth elements where the 4f electrons remain largely inert. Rare +2 oxidation states are observed in specific compounds, such as certain iodides and organometallic complexes, while +4 states are uncommon and limited to unstable or specialized species like fluorides under extreme conditions. This predominance of the +3 state arises from the stability of the half-filled to nearly filled 4f subshell, with Er³⁺ having a [Xe] 4f¹¹ configuration.[5][13] In terms of reactivity, erbium metal slowly tarnishes in air at room temperature, forming a protective layer of erbium(III) oxide (Er₂O₃) upon exposure to oxygen. It reacts more vigorously with water, particularly hot water, producing erbium(III) hydroxide (Er(OH)₃) and hydrogen gas (H₂), though the reaction is slower with cold water due to the metal's moderate electropositivity. Erbium also dissolves readily in dilute acids, such as sulfuric acid, to yield solutions of Er³⁺ salts and hydrogen gas, demonstrating its amphoteric tendencies typical of lanthanides.[14][15][14] The Er³⁺ ion has an ionic radius of 89 pm in six-coordinate environments, a value reduced compared to lighter lanthanides due to the lanthanide contraction, where progressive filling of the 4f orbitals shields nuclear charge poorly, leading to stronger effective nuclear attraction and smaller atomic sizes across the series. This contraction influences erbium's bonding, favoring high coordination numbers in complexes. Erbium forms stable coordination compounds with multidentate ligands such as ethylenediaminetetraacetic acid (EDTA), typically exhibiting coordination numbers of 6 to 9, which accommodate the ion's large size and high charge density. Electrochemical studies indicate a standard reduction potential of E°(Er³⁺/Er) ≈ -2.3 V versus the standard hydrogen electrode (SHE), underscoring erbium's strong reducing nature and tendency to form the +3 cation in aqueous solutions.[10]Isotopes
Erbium has six stable isotopes: ^{162}Er, ^{164}Er, ^{166}Er, ^{167}Er, ^{168}Er, and ^{170}Er. Their natural abundances are as follows:| Isotope | Abundance (%) |
|---|---|
| ^{162}Er | 0.139 |
| ^{164}Er | 1.61 |
| ^{166}Er | 33.503 |
| ^{167}Er | 22.895 |
| ^{168}Er | 27.08 |
| ^{170}Er | 14.873 |