IonSource Atomic Weights

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Atomic Weights for a Select Subset of Biologically Relevant  Elements    
Element Atomic Weight
Hydrogen H 1.00794(7)
Carbon C 12.0107(8)
Nitrogen N 14.0067(2)
Oxygen O 15.9994(3)
Sulfur S 32.065(5)
. . .
Fluorine F 18.9984032(5)
Sodium Na 22.989770(2)
Magnesium Mg 24.3050(6)
Phosphorus P 30.973761(2)
Chlorine Cl 35.453(2)
Potassium K 39.0983(1)
Calcium Ca 40.078(4)
Manganese Mn 54.938049(9)
Iron Fe 55.845(2)
Copper Cu 63.546(3)
Bromine Br 79.904(1)
Iodine I 126.90447(3)
Atomic Weight is an average weight of the isotopes which takes in to account and weights the abundance of the naturally occurring isotopes to obtain the final atomic weight.  Hint: Use atomic weight to calculate the average mass of a molecule.  Note: (1) Since atomic weight is the product of measured physical characteristics the significant number furthest to the right carries an uncertainty (n).  For example The atomic weight of sulfur is 32.066 0.006.  Reference: IUPAC Commission on Atomic Weights and Isotopic Abundances, Atomic Weights of the Elements, Pure Appl. Chem.,71, 1593-1607, (1999).  The full list can be found presented on the web at the following site
For our list there have been recent updates for N, S, Cl, see link below
Pure Appl. Chem. Vol. 73, No. 4, pp. 667-683 (2001) table updated to these new values.
New IUPAC Publication: ATOMIC WEIGHTS OF THE ELEMENTS 2001, Pure Appl. Chem., Vol. 75, No. 8, pp. 11071122, 2003. .pdf  
No changes made to the elements shown on this page as the result of this publication.


History: Isotopes and Atomic Weights

Link to IUPAC periodic table with atomic weights to five significant figures.

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