Column Descriptions Relative Isotopic Standard Isotope Atomic Mass Composition Atomic Weight Notes _________________________________________________________________________ 8 O 16 15.99491461957(17) 0.99757(16) [15.99903,15.99977] 17 16.99913175650(69) 0.00038(1) 18 17.99915961286(76) 0.00205(14) _________________________________________________________________________NIST | Physical Measurement Laboratory | Physical Reference Data | Atomic Weights and Isotopic Compositions Main Page