Atomic weight intervals also affect molecular weight intervals for molecules made up of atoms coloured pink on the IUPAC Periodic Table of the Elements and Isotopes.
Specific atomic weight intervals for hydrogen and carbon atoms from different sources of methane (CH4) are listed on the previous charts.
We can calculate the molecular weight interval for methane from the atomic weight intervals of its constituent atoms, as follows:
Mr(CH4)lower bound = 4(Ar(H)lower bound) + 1(Ar(C)lower bound)
Mr(CH4)upper bound = 4(Ar(H)upper bound) + 1(Ar(C)upper bound)
Source-specific atomic weight intervals from samples of atmospheric methane are:
- Hydrogen in methane (atmosphere): [1.00795, 1.00797]
- Carbon in methane (atmosphere): [12.01054, 12.01067]
Using these atomic weight intervals, calculate the molecular weight interval for atmospheric methane:
Mr(CH4)lower bound = 4(1.00795) + 1(12.01054) = 16.04234
Mr(CH4)upper bound = 4(1.00797) + 1(12.01067) = 16.04255
We then will insert our two calculated values into the format for atomic weights and molecular weights: [lower bound, upper bound].
Our final answer is: [16.04234, 16.04255]
Source-specific atomic weight intervals from samples of freshwater methane are:
- Hydrogen in methane (fresh water): [1.00792, 1.00795]
- Carbon in methane (fresh water): [12.01016, 12.01055]
Mr(CH4)upper bound = 4(1.00795) + 1(12.01055) = 16.04235