This table is based on the 2011 table after the IUPAC (International Union of Pure and Applied Chemistry), Commission on Isotopic Abundances and Atomic Weights. It is important to note that row names are the symbol of the elements.
References
Wieser, M.E., and others. 2013. Pure and Applied Chemistry. International Union of Pure and Applied Chemistry (IUPAC). v. 78, no. 11, pp. 2051--2066.