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very urgent a level chem question

Once the radicals have formed, they are highly reactive. Give the equations for two propagation steps that occur in the reaction of ethane with chlorine.

For this question, i got the reactions right but the mark scheme says this:
DO NOT ALLOW dots on molecules

Why is that? I drew the correct reactions but lost two marks because i put dots on the radicals
I have my exam tomorrow so I would really appreciate if someone could respond quickly
Original post by lifeofpablo1
Once the radicals have formed, they are highly reactive. Give the equations for two propagation steps that occur in the reaction of ethane with chlorine.

For this question, i got the reactions right but the mark scheme says this:
DO NOT ALLOW dots on molecules

Why is that? I drew the correct reactions but lost two marks because i put dots on the radicals
I have my exam tomorrow so I would really appreciate if someone could respond quickly


You can only put "dots" on radicals. If you put a "dot" on a molecule it must have gained an electron.

Cl2 ==> 2Cl•

Cl• + C2H6 ==> C2H5 + HCl

C2H5 + Cl2 ==> C2H5Cl + Cl•

etc.
molecule refers to cl2 for example. cannot put a dot there
okay thank you both
Original post by charco
You can only put "dots" on radicals. If you put a "dot" on a molecule it must have gained an electron.

Cl2 ==> 2Cl•

Cl• + C2H6 ==> C2H5 + HCl

C2H5 + Cl2 ==> C2H5Cl + Cl•

etc.


wait i wrote the second equation and the third exactly as you just wrote them, but in the mark scheme it said do not allow dots on molecules. heres the question and mark scheme if you want to take a lookScreenshot 2023-06-11 at 22.06.04.pngScreenshot 2023-06-11 at 22.06.30.png
Original post by lifeofpablo1
wait i wrote the second equation and the third exactly as you just wrote them, but in the mark scheme it said do not allow dots on molecules. heres the question and mark scheme if you want to take a lookScreenshot 2023-06-11 at 22.06.04.pngScreenshot 2023-06-11 at 22.06.30.png


My interpretation of this marks scheme is that you don't need to include the single electron on the radicals BUT you will be marked incorrect if you place a dot on a molecule.

So, the equations I wrote are correct, and the versions that do not show the unpaired electron will also be marked correct, BUT molecules that are not free radicals will be marked incorrect if an unpaired electron is shown.

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