Write about Thulium atom.

     

Thulium is a chemical element with the symbol Tm and atomic number 69.  It is the thirteenth and third-last element in the lanthanides series.  Like the other lanthanides, the most common oxidation state is +3, seen in its oxide, halides and other compounds; because it occurs so late in the seires, however, the +2 oxidation state is also stabilized by the nearly full 4f shell that results.  In aqueous solution, like compounds of other late lanthanides, soluble thulium compounds form coordination complexes with the nine water molecules.  

     In 1879, the Swedish chemist Per Teodor Cleve separated from the earth oxide erbia another two previously unknown components, which he called holmia and thulia, these were the oxides of holmium and thulium, respectively.  A relatively pure sample of thulium metal was first obtained in 1911.

     Thulium is the second-least abundant of the lanthanides, after radioactively unstable promethium which is only found in trace quantities o Earth.  It is an easily workable metal with a bright silvery-gray luster.  It is fairly soft and slowly tarnishes in air.