Trends in ionization energy in the second period [closed]








**Closed.** This question is [off-topic](/help/closed-questions). It is not currently accepting answers.
 
 






---








 **Homework questions** must demonstrate some effort to understand the underlying concepts. For help asking a good homework question, see: [How do I ask homework questions on Chemistry Stack Exchange?](https://chemistry.meta.stackexchange.com/questions/141/how-do-i-ask-homework-questions-on-chemistry-stack-exchange)




Closed 5 years ago.








[Improve this question](/posts/91590/edit) 




> 
> **Question**  
> 
>  Which element among the following has the highest ionisation energy: fluorine, oxygen, neon. 
> 
> 
> 


I know that all these elements belong to period 2 and ionisation energy increases from left to right across a period. But is there going to be an exception for neon? Or is it that Neon will also follow the normal rule?




Compared with oxygen and fluorine, neon has to ionize an electron from the same subshell (2p) and there is more nuclear charge holding that subshell down. Neon thus requires the highest energy to ionize.


Now consider the process of *accepting* an electron. Oxygen and fluorine can do so in their 2p subshell but in neon that is full, the electron has to go into a higher subshell like 3s. That limits the electron affinity of neon.


So neon is hard to knock an electron out and yet does not release much energy accepting an electron. Add that up and you get ... an essentially inert element! Like ... neon.


 1