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From Chemguide:

That means that the only elements to form positive ions with noble gas structures (apart from odd ones like scandium) are those in groups 1 and 2 of the Periodic Table and aluminium in group 3 (boron in group 3 doesn't form ions).

Negative ions are tidier! Those elements in Groups 5, 6 and 7 which form simple negative ions all have noble gas structures.

Does it mean that generally negative ions are luckier in achieving the noble gas form? Is there any trend behind this, or is it just a coincidence?

Why did he chose those particular three groups as an example? There are negative ions formed by elements in other groups too.

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  • $\begingroup$ Can you give an example of what you mean by your last sentence? $\endgroup$ – orthocresol May 1 '16 at 9:29
  • $\begingroup$ @orthocresol - the oxygen anion, $\ce{O^2-}$ I wanted to take $\ce{Al(OH)_4}$ as an example, but recalled that it's a complex ion. I just did not understand clearly what the author meant. $\endgroup$ – CowperKettle May 1 '16 at 9:50
  • $\begingroup$ "Groups 5, 6, and 7" actually refers to Groups 15, 16, and 17 according to the current nomenclature, i.e. the N, O, F groups. $\endgroup$ – orthocresol May 1 '16 at 10:36
  • $\begingroup$ @orthocresol - and simple ions are formed only by elements in those three groups? $\endgroup$ – CowperKettle May 1 '16 at 10:38
  • $\begingroup$ No, but the simple ions that are formed will have noble gas configurations. For example you don't see $\ce{O-}$ or $\ce{N^2-}$ but you do see $\ce{O^2-}$ and $\ce{N^3-}$. $\endgroup$ – orthocresol May 1 '16 at 10:39

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