Ytterbium
Physical properties

Ytterbium is a soft, malleable and ductile chemical element. When freshly prepared, it is less golden than cesium, but, more golden in color than just a "yellow-cast" as in metals like iridium. It is a rare-earth element, and it is readily dissolved by the strong mineral acids.

Ytterbium has three allotropes labeled by the Greek letters alpha, beta and gamma. Their transformation temperatures are −13 ° C and 795 °C, although the exact transformation temperature depends on the pressure and stress. The beta allotrope (6.966 g/cm) exists at room temperature, and it has a face-centered cubic crystal structure. The high-temperature gamma allotrope (6.57 g/cm) has a body-centered cubic crystalline structure. The alpha allotrope (6.903 g/cm) has a hexagonal crystalline structure and is stable at low temperatures. The beta allotrope has a metallic electrical conductivity at normal atmospheric pressure, but it becomes a semiconductor when exposed to a pressure of about 16,000 atmospheres (1.6 GPa). Its electrical resistivity increases ten times upon compression to 39,000 atmospheres (3.9 GPa), but then drops to about 10% of its room-temperature resistivity at about 40,000 atm (4.0 GPa).

In contrast to the other rare-earth metals, which usually have antiferromagnetic and/or ferromagnetic properties at low temperatures, ytterbium is paramagnetic at temperatures above 1.0 kelvin. However, the alpha allotrope is diamagnetic. With a melting point of 824 °C and a boiling point of 1196 °C, ytterbium has the smallest liquid range of all the metals.

Contrary to most other lanthanides, which have a close-packed hexagonal lattice, ytterbium crystallizes in the face-centered cubic system. Ytterbium has a density of 6.973 g/cm, which is significantly lower than those of the neighboring lanthanides, thulium (9.32 g/cm) and lutetium (9.841 g/cm). Its melting and boiling points are also significantly lower than those of thulium and lutetium. This is due to the closed-shell electron configuration of ytterbium (4f 6s), which causes only the two 6s electrons to be available for metallic bonding (in contrast to the other lanthanides where three electrons are available) and increases ytterbium's metallic radius.
punctuation:no_comma, language:response_language[French]