Thulium and Silicon in Chemistry World’s Element: Ultima Thule to Medical Lasers and Semiconductors

In this Chemistry World Element episode, the editors explore Thulium, its discovery in the late 19th century, and its surprising medical and laser applications, before turning to Silicon and its dominance in today’s electronics. The discussion interweaves history, isotopes, and practical applications with a nod to the origins of the element's name and its place among the rare earths.

• Thulium’s discovery and Ultima Thule roots
• The Nobel Prize context tied to Thulium's study and atomic weight work
• Transition to Silicon and its doping driven semiconductor behavior

Overview

In the podcast the Chemistry World Editorial escorts listeners through the story of Thulium, a relatively obscure lanthanide that sits among the rare earths. The host delves into the historical intrigue surrounding Thulium, including Pere Theodore Cleve’s 1879 misnaming and the mythic Ultima Thule that inspired the name. The discussion ties the element to a broader narrative about how early ore discoveries and oxides led chemists to identify new elements, and how Thulium branded itself as a valuable yet initially underappreciated component of modern chemistry and technology.

The Thulium Story: Discovery and Etymology

The initial traces of erbium and terbium set the stage for thulium’s emergence from the erbium oxide, as Cleve isolated a substance that shifted atomic weights just enough to reveal a new element. Cleve moved Thule to the lanthanide series in a way that both celebrated historic Scandinavian culture and demonstrated the complexities of early periodic-table discoveries. The term Thulium is associated with Thule, a legendary northern land, and while mispositioned, the naming gave the element a lasting resonance in the science narrative.

Thulium in Practice: Abundance, Isotopes and Uses

Thulium is one of the rarer rare earth elements yet remains mined at a measurable scale, with about 50 tonnes produced annually across major mining regions. The most natural isotope, Th-169, is stable, while Th-170—produced in reactors with a half-life of about 128 days—serves as a portable X-ray source. This low-energy source has found applications in small devices used in dentistry and non-destructive testing for cracks in components, illustrating how a niche element can support practical safety and maintenance roles. In another use, thulium doping in a specific garnet structure, Yttrium aluminium garnet (YAG), creates an active medium for lasers with wavelengths around 2000 nm, enabling laser surgery and other medical applications. The narrative also touches on thulium’s limited but real role in medical technologies, underscoring the element’s contributions even as it remains less commercial than other rare earths.

The Nobel Link and the Thule Connection

The podcast highlights Theodore William Richards, who received the Nobel Prize in 1914 for his methodical and rigorous determination of atomic weights across many elements. The Thulium-specific aspect of Richards’s work is remarkable: 15 000 recrystallization experiments were required to obtain a pure sample of thulium bromate to fix its atomic weight with precision. The discussion uses this anecdote to illustrate the relentless, empirical spirit of early 20th-century chemistry and how the pursuit of exact atomic weights can become a Nobel-worthy pursuit. Cleve’s naming story and Richards’s painstaking measurements together frame Thulium’s place in the history of chemistry.

Thulium’s Place Among the Lanthanides and the Era of Rare Earths

The piece situates Thulium toward the end of the lanthanide series, reflecting its historical and commercial characterization as a rare and valuable, though not ubiquitously scarce, element. The dialogue also clarifies how the concept of “rare earths” often masks the reality that many of these elements are relatively common in the Earth’s crust, but their ores can be geographically and economically constrained. This context helps explain why Thulium, while not a mass-market element, remains scientifically and technologically significant.

Transition: Silicon and the Everyday Tech Connection

The element shift in the episode turns to Silicon, describing its dark grey appearance and glass-like luster while emphasizing its status as a poor conductor in pure form. The host explains how deliberate impurities, such as boron or phosphorus, modulate silicon’s electrical properties to create the backbone of modern electronics, including the silicon chips that power our devices. The segment underscores Silicon’s centrality to everyday technology and hints at the broader theme of the Element series: how the right material, treated the right way, becomes foundational to modern life.

Concluding Theme

The podcast closes with a note about next week’s element, maintaining the series’ mission to illuminate the chemistry behind everyday life and innovation. The overall narrative weaves history, practical applications, and forward-looking chemical relevance into a compact exploration of Thulium and Silicon.