Масени број — разлика између измена

* {{Cite book |ref= harv|last=Bishop |first=Mark |title=An Introduction to Chemistry |url=http://preparatorychemistry.com |accessdate = 8. 7. 2008. |publisher=Chiral Publishing |isbn=978-0-9778105-4-3 |pages=93 |chapter=The Structure of Matter and Chemical Elements (ch. 3) |chapterurl=http://preparatorychemistry.com/Bishop_Book_atoms_3.pdf| ref = harv}}