Ductility
Ductility can be quantified by the fracture strain formula_1, which is the engineering strain at which a test specimen fractures during a uniaxial tensile test. Another commonly used measure is the reduction of area at fracture formula_2. The ductility of steel varies depending on the alloying constituents. Increasing the levels of carbon decreases ductility. Many plastics and amorphous solids, such as Play-Doh, are also malleable.
The most ductile metal is platinum and the most malleable metal is gold.
Thallium hydride
Thallium hydride is the simplest thallane. Thallium is the heaviest member of the Group 13 metals; the stability of group 13 hydrides decreases with increasing periodic number. This is commonly attributed to poor overlap of the metal valence orbitals with that of the 1s orbital of Hydrogen. Despite encouraging early reports, it is unlikely that a thallium hydride species has been isolated. Thallium hydrides have been observed only in matrix isolation studies; the infrared spectrum was obtained in the gas phase by laser ablation of thallium in the presence of hydrogen gas. This study confirmed aspects of ab initio calculations conducted by Schwerdtfeger which indicated the similar stability of thallium and indium hydrides. There has not been a confirmed isolation of a thallium hydride complex to date.