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[[File:ElementTile.png|right|400px|thumb|An [[element]] tile showing the '''mass number'''.]]

The '''relative atomic mass''' or '''mass number''' of an [[element]] is the number of [[nucleon]]s ([[proton]]s + [[neutron]]s) in an [[atom]].

The '''relative atomic mass''' in [[gram]]s is also the [[mass]] of one [[mole]] or [[Avagadro Constant|6.02x10²³]] [[atom]]s of the [[element]].