hypervalent_iodine Posted January 7, 2020 Share Posted January 7, 2020 2 hours ago, Rachel Maddiee said: Carbon has formed three covalent bonds in the structure so it would have 7 electrons around it (not 8 as shown) Likewise the oxygen fails to follow the rule. No. This was wrong in your first answer and it’s still wrong here. Both the carbon and the oxygen in the Lewis structure in the question have 8 electrons around them. Both satisfy the octet rule. I’m not sure how else to explain this, so perhaps I will work on something later and you can review the posts in this thread in the meantime. 2 hours ago, Rachel Maddiee said: There should be two pairs of electrons (a double bond) between the C and O, and no lone pair on the C. Yes, but how do you know that? Saying that carbon has to have four bonds isn’t good enough reasoning, because that statement isn’t always true. Same for oxygen. Please go through the post I made in response to MigL. It works through this aspect of the problem. 4 hours ago, Rachel Maddiee said: Incorrect structure: 8 bonding electrons and 2 lone pairs Number of electrons = 6 + 8 = 14 total electrons Correct structure; CH2O There are 4 valence electrons in carbon, 1 each in hydrogen and 6 in oxygen, so there are 12 electrons total Great! So what does this tell you about the Lewis structure? 4 hours ago, studiot said: I suggest you stick to the dots. Because of the many exceptions the dot structure is taught and then students move on. So I also suggest you do enough to earn the marks (since you must and HI doesn't need to) but remember better methods follow My comment was made for two reasons. Based on the OP, Rachel is perfectly comfortable using lines to represent bonds and can tell that each bond has two electrons in it. The second reason is that it is not standard notation and when you get to later topics or even when you get further into drawing Lewis structures, using dot notation to represent bonds is confusing. Many higher institutions will mark you wrong or deduct marks for using this notation - it is a bad habit to fall in to. It is truly the bane of our first year teaching staff’s existence. They take this notation from this topic and start drawing bonds as dots when covering, for example, organic chemistry. We have systematic methods of drawing structures for a reason! The other rather irritating part is that it is taught differently and inconsistently in different schools and so there is a lot to have to stamp out. Link to comment Share on other sites More sharing options...
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