What is relative atomic mass?
Q: What is relative atomic mass?
A: Relative atomic mass (also called atomic weight; symbol: Ar) is a measure of how heavy atoms are. It is the ratio of the average mass per atom of an element from a given sample to 1/12 the mass of a carbon-12 atom. In other words, it tells you the number of times an average atom from a given sample is heavier than one-twelfth of an atom of carbon-12.
Q: What does "relative" in relative atomic mass mean?
A: The word "relative" in relative atomic mass refers to this scaling relative to carbon-12, meaning that it measures the ratio between two masses rather than having any specific units itself.
Q: How do isotopes differ from each other?
A: Isotopes are atoms with different numbers of neutrons, which means they have different masses and thus different relative isotopic masses. For example, thallium has two common isotopes - thallium-203 and thallium-205 - both with 81 protons but differing in their number of neutrons (122 for 203 and 124 for 205).
Q: How can we calculate the relative atomic mass for a sample?
A: We can find the relative atomic mass by calculating the abundance-weighted mean of its respective isotope's relative isotopic masses. For example, if a sample consists 30% thallium-203 and 70% thallium-205 then we would calculate A_r = (203 x 30) + (205 x 70)/100 = 204.4.
Q: What is standard atomic weight?
A: Standard Atomic Weight is the mean value of all normal samples' respective Relative Atomic Masses published at regular intervals by IUPAC (International Union Of Pure And Applied Chemistry). This value appears on periodic tables as well as being used interchangeably with Relative Atomic Mass when referring to individual samples or elements.
Q: How could samples taken from different locations vary in terms of their Relative Atomic Masses?
A: Samples taken from different locations may have slightly different Relative Atomic Masses due to differences in proportions between each element's respective isotopes at those locations.
