What is Relative atomic mass?
A '''relative atomic mass''' (also called '''atomic weight'''; symbol: ''A''<sub>r</sub>) is a measure of how heavy [[atom]]s are. It is the [[ratio]] of the average mass per atom of an [[Chemical element|element]] from a given sample to 1/12 the mass of a [[carbon-12]] atom.<ref name=iupac1 >{{cite web|url=http://www.ciaaw.org/atomic_weights2.htm|title=Atomic weight: The Name, its History, Definition, and Units|publisher=Commission on Isotopic Abundances and Atomic Weights of the International Union of Pure and Applied Chemistry|accessdate=2016-01-07|archive-date=2013-12-15|archive-url=https://web.archive.org/web/20131215231731/http://www.ciaaw.org/atomic_weights2.htm|url-status=bot: unknown}}</ref><ref>{{cite book|editor=Daintith, John|title=A Dictionary of Chemistry|url=https://archive.org/details/dictionarychemis00dain|publisher=Oxford University Press|page=[https://archive.org/details/dictionarychemis00dain/page/457 457]|date=2008|edition=Sixth|isbn=978-0-19-920463-2}}</ref> In other words, a relative atomic mass tells you the number of times an average atom of an element from a given sample is heavier than one-twelfth of an atom of carbon-12. The word ''relative'' in relative atomic mass refers to this scaling relative to carbon-12. Relative atomic mass values are ratios;<ref name=salters>{{cite book|editor1=Otter, Chris|editor2=Stephenson, Kay|title=Salters Advanced Chemistry: Chemical Ideas|url=https://archive.org/details/saltersadvancedc0000unse_k7t3|publisher=Heinemann|date=2008|edition=Third|isbn=978-0-435631-49-9}}</ref>{{rp|1}} relative atomic mass is a [[dimensionless quantity]]. Relative atomic mass is the same as ''atomic weight'', which is the older term. The number of [[proton]]s an atom has determines what element it is. However, most elements in nature consist of atoms with different numbers of [[neutron]]s.<ref name=salters />{{rp|17}} An atom of an element with a certain number of neutrons is called an [[isotope]].<ref name=moore>{{cite book|first=John T.|last=Moore|title=Chemistry Essenti