Mendelevium

Atomic number: 101

Symbol: Md (Mv before the 1960s)

Category: actinide 

Density at 25°C: solid: density: n/a

This element is formed by smashing alpha particles into einsteinium. Named after named after Dmitri Ivanovich Mendeleev, who developed the Periodic Table.  The longest lived isotope is 258Md with a half life of 51.5 days.