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chemistry gcse

i was just wondering how do you know if a simple molecule has a triple or double bond
for example how would you know how to draw the dot and cross diagram for CO2
(edited 9 months ago)
Reply 1
Original post by grey_cloud
i was just wondering how do you know if a simple molecule has a triple or double bond
for example how would you know how to draw the dot and cross diagram for CO2

You rarely see triple bonds but at GCSE the only thing that form triple bonds is something like nitrogen.
The tip with dot and cross diagrams is to know how many electrons an atom needs to gain a full outer shell, and so the number of bonds needed will match how many electrons. At GCSE they aren't really going to give you anything more complex in a dot and cross diagram than a simple molecule like CO2 or NH3 or HCl which should usually balance out on the number of electrons. Just keep in your head that carbon needs 4 bonds, nitrogen needs 3 bonds, oxygen needs 2 bonds, chlorine and hydrogen needs 1 bond, etc.
for your example on CO2 the carbon needs 4 bonds while each of the oxygen atoms needs 2 bonds, so to give all atoms a full outer shell you need each oxygen forming a double bond with carbon, like O=C=O. Another thing to be mindful of is making sure the atoms have the number of electrons outside the bonds, eg. if there are 4 electrons in the bond between oxygen and carbon there must be 4 more electrons that are on the oxygen but are unbonded - make sure to include these or you lose marks. At GCSE you sould just be counting 2 or 8 electrons in the outer shell or the bond
Reply 2
Thank you so much!
The co2 dot and cross diagram was asked int he 2023 paper and when i did it as practise i put three electrons being shred between each oxygen and carbon
i am i right in saying i was wrong because covalent bonds are shared pair of electrons so they can't be in an odd number? if that makes sense
Reply 3
Original post by grey_cloud
Thank you so much!
The co2 dot and cross diagram was asked int he 2023 paper and when i did it as practise i put three electrons being shred between each oxygen and carbon
i am i right in saying i was wrong because covalent bonds are shared pair of electrons so they can't be in an odd number? if that makes sense

yh both atoms have to contribute 1 electron each per bond so it's always even
Reply 4
main thing is to make sure you give all of the atoms a full outer shell of 2 or 8 electrons
Reply 5
thank you so much
Reply 6
I am doing my Chem paper tom and I am set as foundation if I ask for a higher paper will they give it me because there’s no teachers so they don’t know
Reply 7
Original post by Tidbfhf78
I am doing my Chem paper tom and I am set as foundation if I ask for a higher paper will they give it me because there’s no teachers so they don’t know

you're registered to do a foundation paper by the exam board so idt it would be valid if you did the higher paper instead
Original post by Tidbfhf78
I am doing my Chem paper tom and I am set as foundation if I ask for a higher paper will they give it me because there’s no teachers so they don’t know

If you've been registered for foundation then you probably need to do foundation.

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