Ytterbium (Yb)

• Element Symbol: Yb
• Atomic Number: 70
• Atomic Mass: 173.04
• Group # in Periodic Table: n/a
• Group Name: Lanthanides
• Period in Periodic Table: 6
• Block of Periodic Table: f-block
• Discovered by: Jean Charles Galissard de Marignac (1878)

Ytterbium is a metallic chemical element of the periodic table. It is a rare earth metal belonging to the lanthanide group of elements, which includes fourteen other rare earth elements, such as lanthanum and samarium. Rare earth elements typically occur together in nature and are oftentimes difficult to separate.

In 1787 a mineral called gadolinite was discovered in a quarry outside the small Swedish town of Ytterby. It was from this mineral that the first known rare earth element, yttrium (named after the nearby town), was discovered in 1789 by Johan Gadolin. As would later prove common with rare earth metals, it was believed that this sample of yttrium contained additional elements. In 1843 this belief was proved to be true when Carl Mosander successfully separated the elements erbium and terbium from yttrium.

In 1878, Swiss chemist Jean Charles Galissard de Marignac successfully extracted yet another new element—ytterbium. In order to isolate this element, de Marignac decomposed erbium nitrate by heating it up, resulting in a residue that he extracted with water. This process resulted in the production of two oxides, one red, which de Marignac knew to be erbium oxide, and one white, which he concluded must be a new element, ytterbium. In total, there are four elements that are named for the town of Ytterby, Sweden: ytterbium, yttrium, terbium, and erbium. The physical and chemical properties of ytterbium could not be properly studied until 1953, when scientists A. Daane, Frank Spedding, and David Dennison at the Ames Laboratory in Iowa produced the first pure metal sample of ytterbium.

Physical Properties

Ytterbium is a bright silver metallic color. At 298 kelvins (K), ytterbium’s standard state is a soft, malleable solid; in this state it has a density of 6.97 grams per cubic centimeter (g/cm³). Ytterbium is susceptible to corrosion when exposed to air and begins to oxidize at room temperature, developing a protective oxide layer on its surface. To prevent oxidation, ytterbium is commonly kept in airtight vessels that are filled with an inert gas.

The melting point of ytterbium is 824 degrees Celsius (°C), and its boiling point is 1196 °C, making ytterbium’s liquid range the smallest of all the metals. The specific heat of ytterbium at 298 K is 154 joules per kilogram-kelvin (J/kg·K). As a metal, ytterbium is a good conductor, with an electrical conductivity of 3.6 × 10⁶ siemens per meter (S/m), but it becomes a semiconductor under pressures of more than 16,000 atmospheres. Ytterbium has a thermal conductivity of 39 watts per meter-kelvin (W/m·K). It is paramagnetic, meaning that it is magnetized when placed within a magnetic field but does not retain this property once removed from the field.

Chemical Properties

Common oxidation states of ytterbium are +3 and +2. Ytterbium is easily dissolved by mineral acids, but it reacts slowly with water. Naturally occurring ytterbium is made up of seven stable isotopes, the most abundant of which is ytterbium-174. In addition to these seven, ytterbium also has twenty-seven radioactive isotopes. Ytterbium-169, ytterbium-175, and ytterbium-166 are the most stable of these isotopes, with half-lives of 32 days, 4.18 days, and 56.7 hours, respectively. The remaining twenty-four radioactive isotopes all have half-lives of less than two hours, and in most cases less than twenty minutes. Unstable ytterbium isotopes with mass numbers less than 174 (ytterbium’s most stable isotope) undergo electron capture, a form of radioactive decay in which an atom’s electron is absorbed by the nucleus and combines with a proton to form a neutron and a neutrino. Ytterbium isotopes that undergo electron capture produce thulium isotopes. Unstable ytterbium isotopes with mass numbers greater than isotope 174 undergo beta decay, another form of radioactive decay, in which a proton is converted into a neutron (or vice versa) inside the nucleus of an atom; when the atom goes through this process, energy is released in the form of a beta particle (a fast-moving electron or positron). In ytterbium, the process usually results in isotopes of lutetium.

At room temperature, ytterbium has a face-centered cubic structure. Additionally, three allotropes (different structural configurations) exist, undergoing transformations at −13 °C and 795 °C.

Applications

Despite the name "rare earth element," such elements are usually quite abundant on Earth, occurring naturally in many different sources. Ytterbium is one of the least abundant of the rare earth metals, existing in Earth’s crust at three parts per million. Ytterbium is not found freely in nature but is present in minerals such as monazite, gadolinite, and xenotime. It is from monazite sand, which is made up of approximately 0.03 percent ytterbium, that the element is most often extracted through processes such as ion exchange and solvent extraction. Before these more modern techniques were developed in the mid-1900s, rare earth metals were notoriously difficult (and therefore expensive) to isolate. Ytterbium is primarily mined in China, the United States, and India, with about fifty tons of ytterbium being produced each year.

Ytterbium serves no major biological role, but it is known to be irritating to the skin and eyes. Ytterbium is considered to be only moderately toxic, but all of its compounds are regarded as highly toxic and should be treated with caution. Metallic ytterbium dust is particularly dangerous, as it can spontaneously combust under specific conditions. The resulting flames of an ytterbium explosion are extremely hazardous and cannot be put out using water or traditional fire extinguishers.

Ytterbium-169, one of the element’s radioactive isotopes, emits gamma rays, making it a useful tool in radiography. Particularly useful when no electricity is accessible, the isotope acts like a miniature x-ray machine. Ytterbium is also used as an alloy for improving the strength and grain refinement of stainless steel. Due its high electrical resistance under physical stress, the element is also used in stress gauges that monitor the effects of events such as earthquakes. Additionally, ytterbium is utilized in solid-state lasers due to its highly efficient and long-lasting nature.

Bibliography

Atwood, David A., ed. The Rare Earth Elements: Fundamentals and Applications. Hoboken: John Wiley & Sons, 2012. Print.

Haynes, William M., ed. CRC Handbook of Chemistry and Physics. 95th ed. Boca Raton: CRC, 2014. Print.

Lucas, Jacques, et al. Rare Earths: Science, Technology, Production and Use. Waltham: Elsevier, 2015. Print.

"Technical Data for Ytterbium." The Photographic Periodic Table of the Elements. Element Collection, n.d. Web. 9 Aug. 2015.

"Ytterbium (Yb)." Encyclopaedia Britannica. Encyclopaedia Britannica, 8 July 2014. Web. 9 Aug. 2015.