Achieve week 5 question number 4

[205696437]

"The observed carbon–oxygen bond lengths in carbamate are both 128 pm, whereas the observed carbon–nitrogen bond length is 136 pm. Expected values are shown in the table. Based on the Lewis structures and the bond length data, select the correct statement or statements." Can someone help explain this part to me because I'm really lost

[Lily Zello 3I]

Hi! Which part are you confused about? If you're asking about the numbers, part of this has to do with resonance, a topic Lavelle taught about in the 10/25 lecture. Resonance is the blending of lewis structures that occurs when lewis structures have bonds in multiple locations (such as NO3-). The observed bond lengths of these types of molecules are usually in between that of the single bond and the double bond because the actual molecule demonstrates a blend of the various lewis structures, with each bond having a partial double bond character. So, in the question, we see that the observed carbon–oxygen bond lengths in carbamate are both 128 pm, a value in between the expected single bond length and the expected double bond length. The same goes for the carbon-nitrogen bond length. Is this what you were asking?

[205678283]

Hi! Okay so do not overthink this! We are just comparing the numbers that they gave us - no math involved! If the observed length of our carbon-oxygen bond is 128 pm, and the expected length of the C=O bond is 112 pm, but the C-O bond is 143, the carbon-oxygen bond has ample C=O bond character and not C-O character because 112<128, but 143>128. The expected has to be less than the observed. Likewise, for the carbon-nitrogen bond, if the observed value is 136 pm, and the C=N bond is 127 pm but the C-N is 152 pm, it has ample C=N character because 127<136, but 152>136.