Explain why the positions of cobalt and nickel do not appear to be reversed in periodic tables where the relative atomic masses are rounded to a whole number?

1 Answer
anor277
Feb 26, 2018

Would this not be expected?

Explanation:

The modern Periodic Table orders elements solely on the basis of #Z#, #"the atomic number"#, where #Z-="the number of positively charged NUCULAR particles."# #Z# defines the identity of the element.

For #Co#, #Z=27#, and for #Ni#, #Z=28#, and thus even tho they have similar atomic masses, the order given on the Periodic Table is CORRECT.

And as atomic masses go, #Ni, 58.7*g*mol^-1#, and #Co, 58.9*g*mol^-1#, i.e. the most stable cobalt nuclides contain more neutrons than nickel....but this does not alter the atomic number, and their order of appearance on the Table is correct.

For another example of this, see the atomic weights of curium, #Z=96#, versus berkelium, #Z=97#...

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