HomeElement listsEra of discoveryEarly quantum theories (1900–1949)

Era of discovery: Early quantum theories (1900–1949)

Through new technological possibilities, the emerging quantum age and gained knowledge about radioactivity and its applications, many radioactive elements were found by 1950.

43Tc

Technetiumshiny gray metal

61Pm

Promethiummetallic

63Eu

Europiumsilvery white, with a pale yellow tint; but rarely seen without oxide discoloration

71Lu

Lutetiumsilvery white

72Hf

Hafniumsteel gray

75Re

Rheniumsilvery-grayish

85At

Astatineunknown, probably metallic

Radoncolorless gas

Protactiniumbright, silvery metallic luster

93Np

Neptuniumsilvery metallic

94Pu

Plutoniumsilvery white, tarnishing to dark gray in air

95Am

Americiumsilvery white

96Cm

Curiumsilvery metallic, glows purple in the dark

97Bk

Berkeliumsilvery

H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn Fr Ra Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og

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Enlightenment (until 1799)Element classification (1850–1899)Technical and industrial revolution (1800–1849)Antiquity to Middle Ages Early quantum theories (1900–1949)Synthesis and nuclear sciences (1950–1999)Recent synthesis (since 2000)