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Why is the carbon positive in the third diagram? watch

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    ^^^^^, surely it should be positive as carbon has unbonded pairs of electrons?
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    (Original post by BULL14)
    ^^^^^, surely it should be positive as carbon needs to make four bonds?
    You talking about the middle image?
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    Carbon is not positive in the third diagram because it has been balanced with the negative from the bromide.
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    (Original post by TheBirder)
    Carbon is not positive in the third diagram because it has been balanced with the negative from the bromide.
    sorry the second diagram.
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    (Original post by BULL14)
    ^^^^^, surely it should be positive as carbon has unbonded pairs of electrons?
    Imma just reply and explain each part as I have no clue what you are asking.
    First part, all parts in ethene are neutral as there's 4 bonds to each carbon and the outer bit's hydrogen. the bromine is delta pos and delta neg due to them having formed a permanent dipole attraction, (think of how hydrogen bonds to its self).

    the 2nd image has a positive carbon due to it having "7" electrons 3 of which are shared between the other carbon and the 2 hydrogens. the bromine with the positive (1 less electron) would attach to the carbon to become neutral again as it shares its electron with the carbon, then the negative bromine (1 more electron) attaches to the positive carbon (it's positive as there's 1 less electron in the entire molecule and so it's not neutral.

    the 3rd image is neutral as all the electrons are being shared around.
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    (Original post by BULL14)
    ^^^^^, surely it should be positive as carbon has unbonded pairs of electrons?
    I'm going to get a diagram to explain it better. Its just the polarity of the molecule changes as the electrons move so the bromine can then attach as the bottom bit of the carbon becomes pos due to the electrons moving around.

    https://gyazo.com/0ce575b8201fed929893dad657b4f4d4
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    The diagram is showing Electrophilic Addition of ethene with a bromine molecule. One part of the bromine molecule is electronegative so 'hogs' the electrons in the covalent bond. As a result, the electropositive bromine atom is polarised by the double bond in the ethene molecule, and the molecule of bromine breaks (the electropositive bromine takes both electrons so now has a full outer shell). The electropositive bromine which has just lost an electron causes the double bond in the ethene to break as one of the carbon in the double bond donates the electron in a double bond to the bromine (this is also know as 'electrophilic attack'. The 'positive carbon' you are referring to is called a Carbocation which means that that particular carbon has lost an electron to the bromine, hence the name cation. So that bromine forms a covalent bond with the carbon. The other bromine donates one of its electrons to the carbocation, and also joins onto the ethane molecule as shown in step 2 on this reaction which forms another bromine-carbon covalent bond. In step 3, you see the final product of the electrophilic addition which is called 1,2-dibromoethane. Hope this helps!
 
 
 
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