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What is the largest atom (in terms of volume not atomic mass or weight)? 9/21/99 Vocabulary atomic radius effective nuclear charge lanthanide contraction pm valence electron valence shell Cesium (Cs), tucked in the lower left hand corner of the table, has the largest known atoms.The atomic radius of Cs is given variously as 273.1 pm [1], 265 pm [2], 265.5 pm [3] or 260 pm [4].ubidium also has large atoms, but its atomic radius is almost 30 pm less than cesium's. Why are cesium atoms so big? Cesium has a large valence shell and a relatively low effective nuclear charge. The valence shell (the outer 'peel' of the atom) is largest in atoms at the bottom of the periodic table.
Of the first 82 elements in the periodic table, 80 have isotopes considered to be stable. The 83rd element, bismuth, was traditionally regarded as having the heaviest stable isotope, bismuth-209, but in 2003 researchers in Orsay, France, measured the half-life of 209 Bi to be 7026599594400000000â 1.9Ã1019 years. Technetium, promethium and all the elements with an atomic number over 82 only have isotopes that are known to decompose through radioactive decay. No undiscovered elements are ...