Short answers, pulled from the story.
Jean Charles Galissard de Marignac identified ytterbium in 1878 while examining a sample of gadolinite. He named the element ytterbia after the Swedish village of Ytterby where the original mineral was found. Marignac suspected ytterbia was a compound of a new element but could not isolate the metal itself at that time.
Wilhelm Klemm and Heinrich Bommer produced the first nearly pure metallic ytterbium in 1936. This achievement revealed that the substance was soft, malleable, and ductile with a density of 6.973 grams per cubic centimeter. The metal had not been successfully isolated in pure form before this date despite decades of prior research.
Ytterbium has a melting point of 824 degrees Celsius and a boiling point of 1196 degrees Celsius. These values give the element the smallest liquid range of all metals. The low melting and boiling points result from its unique electronic structure where only two 6s electrons participate in metallic bonding.
When exposed to a pressure of about 16,000 atmospheres, the beta allotrope of ytterbium transforms from a metal into a semiconductor. Its electrical resistivity increases ten times upon compression to 39,000 atmospheres before dropping to about 10 percent of its room-temperature resistivity at approximately 40,000 atmospheres. This pressure-induced phase transition is unique among rare-earth metals.
Experimental atomic clocks based on ytterbium atoms at the National Institute of Standards and Technology set a stability record in 2013. These clocks are accurate within less than two parts in one quintillion and would remain accurate within a second for a period comparable to the age of the universe. The technology relies on about 10,000 ytterbium atoms laser-cooled to 10 microkelvin and trapped in an optical lattice.
Ytterbium is found in minerals such as monazite, euxenite, and xenotime with main mining areas in China, the United States, Brazil, India, Sri Lanka, and Australia. All compounds of ytterbium are treated as highly toxic and can cause irritation to human skin and eyes. Metallic ytterbium dust can spontaneously combust and requires storage in airtight containers within an inert atmosphere.