3.2 Relative Masses of Atoms and Molecules
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31. Define relative atomic mass (Ar).
The average mass of the isotopes of an element compared to 1/12th of the mass of an atom of 12C.
32. Define relative molecular mass (Mr) and when is it specifically used?.
It is the mass of one molecule when compared with 1/12th of the mass of a Carbon-12 atom; it is used specifically for molecules.
33. What is the definition of relative formula mass, and when is it specifically used?
It is the mass of one formula unit when compared with 1/12th of the mass of a Carbon-12 atom; it is used specifically for ionic compounds.
34. What term is used for the Mr of ionic compounds?
Relative formula mass.
35. What is the relative mass of an electron compared to a proton or neutron?
An electron has a relative mass of 1/1840.
36. What is the unit for relative atomic mass (Ar) and relative molecular mass (Mr)?
These values have no units because they are relative comparisons.