name,symbol,mono_mass,average_mass
Hydrogen,H,1.007825035,1.00794
Carbon,C,12.0000000,12.0107
Nitrogen,N,14.003074,14.0067
Oxygen,O,15.99491463,15.9994
Phosphorus,P,30.973762,30.973761
Sulphur,S,31.9720707,32.065
Selenium,Se,79.9165196,79.96