4. Periodic table of the elements14. PERIODIC TABLE OF THE ELEMENTSTable 4.1.Revised 2010 by D.E. Groom (LBNL), and E. Bergren. Atomic weights of stable elements are adapted from the Commission on Isotopic Abundances andAtomic Weights, “Atomic Weights of the Elements 2007,”http://www.chem.qmul.ac.uk/iupac/AtWt/.The atomic number (top left) is the number of protons in thenucleus. The atomic mass (bottom) of a stable elements is weighted by isotopic abundances in the Earth’s surface. If the element has no stable isotope, the atomic mass(in parentheses) of the most stable isotope currently known is given. In this case the mass is fromhttp://www.nndc.bnl.gov/amdc/masstables/Ame2003/mass.mas03and the longest-lived isotope is fromwww.nndc.bnl.gov/ensdf/zaform.jsp. The exceptions are Th, Pa, and U, which do have characteristic terrestrial compositions.Atomic masses are relative to the mass of12C, defined to be exactly 12 unified atomic mass units (u) (approx. g/mole). Relative isotopic abundances often varyconsiderably, both in natural and commercial samples; this is reflected in the number of significant figures given. Previously confirmed element 112 was named
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