قائمة العناصر الكيميائية حسب الكتلة الذرية المعرفة
ملاحظات Note 1 The element does not have any stable nuclides and a value in brackets [209] indicates the mass number of the longest lived isotope of the three elements Thorium Protactinium and Uranium have a characteristic terrestrial isotopic composition and thus their standard atomicweightsaregiven Note 2 The isotopic composition of this element varies in