drea
New Member
Posts: 3 
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Post by drea on Nov 30, 2015 12:38:52 GMT
Dear Sir,
The 1st midterm, there was a question that asked:
Explain why the ionization energy of the elements within a period generally increase from left to right?. My response was: "It increases due to valence shell stability. Going across a period, the valence shell has more electrons added to it, increasing its stability, hence requiring a greater amount of energy to remove an electron. How is this wrong?
Also the question after that . " Explain the anomalous decrease in ionization energy from Be to B
Can you please state the answer for this because I only got 1/2 the marks and do not understand where my answer faultered
Thank you in advance,
Regards
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chad
New Member
Posts: 1 
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Post by chad on Dec 1, 2015 20:35:42 GMT
If i'm not mistaken, what you described is what happens when you move down the group, moving from left to right the I.E increases due to an increase in proton number(increased Zeff), consequently increasing the attractive forces between the outer electrons and the nucleus, thus it would require more energy to overcome the attractive forces to remove an electron.
For the anomaly, Be has a filled 2s sub-shell where as B has one electron in the 2p sub-shell, it would require less energy to remove the 1 electron in the 2p sub shell as opposed to the energy required to break into the filled 2s sub-shell of Be. the 2p sub-shell is also at a higher energy level(slightly further away from the nucleus than the 2s sub-shell) and the attractive forces exerted by the nucleus onto the electron in the 2p sub-shell is slightly less making it easier to remove.
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Post by Admin on Dec 1, 2015 20:57:29 GMT
Hi,
while 'valence shell stability' (VSS) may have some relevance to the question, it does not answer the question completely.
you need to mention two other points for a complete response:(1) effective nuclear charge and (2)screening effect
VSS relates to both of them but is not the same as both. Furthermore VSS applies to explaining the stability of full or half-filled shells.
From what i could remember about the other question, is that most had utilized more than the allotted space to answer the question.
Answers must be concise enough to fit in the spaces provided.- so i think most people did not write concise answers.
In structure type questions where you write in the spaces provided, we only read up to the last 'line' provided (unless someone makes a mistake, crosses it out and has no where else to write, or, if someone needs just 1 mark (not 1%) to pass)
For the final exam, you can write as much as you want to answer a question, but remember dont waste too much time on one part of a question. If a question is 4 marks, it should take 4 minutes to complete- so dont spend more than 5 minutes on it.
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