Qxi.xli
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bit confused about the second step of the reaction. why does the O have a positive charge?
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Sm 002 u mug
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What reaction
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mra1108
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What's the question?
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Qxi.xli
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(Original post by Sm 002 u mug)
What reaction
(Original post by mra1108)
What's the question?
sorry i cant seem to attach an image
its the dehydration of alcohols mechanism x
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Sm 002 u mug
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I’m guessing you are talking about a nucleophilic substitution reaction with water though; the O has a positive charge as it has an extra Hydrogen on it
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Qxi.xli
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(Original post by Sm 002 u mug)
I’m guessing you are talking about a nucleophilic substitution reaction with water though; the O has a positive charge as it has an extra Hydrogen on it
sorry pls find it attached now. its the bit after the second arrow im confused about
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BDavies1
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(Original post by vix.xvi)
sorry pls find it attached now. its the bit after the second arrow im confused about
The O has got a positive charge because a H from the H2SO4 came WITHOUT its electron (i.e. it was an H+ ion) (the HSO4- kept hold of this). One of the lone pairs on the oxygen formed a dative bond to this positive H. Now the positive charge is shared over the -OH2 group..we show it on the diagram as just sitting on the oxygen atom...
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Qxi.xli
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(Original post by BDavies1)
The O has got a positive charge because a H from the H2SO4 came WITHOUT its electron (i.e. it was an H+ ion) (the HSO4- kept hold of this). One of the lone pairs on the oxygen formed a dative bond to this positive H. Now the positive charge is shared over the -OH2 group..we show it on the diagram as just sitting on the oxygen atom...
Thank you!!!
But oxygen technically has a full outer shell right? If you look at my terribly draw dot and cross, it only has a lone pair of electrons right?Name:  16113407806513648157367993432979.jpg
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Davies Chemistry
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yes. But that H on the far left of your diagram came without its own electron (both electrons in the bond are provided by oxygen). That H has a positive proton in its nucleus, but doesn't have a negative electron to balance it-makes the molecule positively charged overall.
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charco
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(Original post by vix.xvi)
bit confused about the second step of the reaction. why does the O have a positive charge?
To convince yourself do some simple maths.

The oxygen has a half share of each bonding pair of electrons = 3 electrons for three bonds.
It "owns" one lone pair.
It has two electrons in the inner 1s orbital
------------------------------------------------------ total electrons "owned" by oxygen
3 + 2 + 2 = 7

But oxygen has a nuclear charge of +8
And each electron has a -1 charge

Hence overall it has a formal charge of -7 + 8 = +1

Name:  alcohol_dehydration.jpg
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Qxi.xli
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(Original post by charco)
To convince yourself do some simple maths.

The oxygen has a half share of each bonding pair of electrons = 3 electrons for three bonds.
It "owns" one lone pair.
It has two electrons in the inner 1s orbital

------------------------------------------------------ total electrons "owned" by oxygen
3 + 2 + 2 = 7

But oxygen has a nuclear charge of +8
And each electron has a -1 charge

Hence overall it has a formal charge of -7 + 8 = +1

Name:  alcohol_dehydration.jpg
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thank you very much
btw, how do you know it has one lone pair and then another 2 electrons? because i thought oxygen has 6 on its outer shell,, it makes three bond pairs, so it has 3 left? sorry this is confusing me alot..
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charco
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(Original post by vix.xvi)
thank you very much
btw, how do you know it has one lone pair and then another 2 electrons? because i thought oxygen has 6 on its outer shell,, it makes three bond pairs, so it has 3 left? sorry this is confusing me alot..
Oxygen is element number 8. It has eight electrons.
There are two electrons in the first shell and six in the second shell. (2,6)

Every time it makes a bond to hydrogen it shares one electron of its own and one from hydrogen.

Thus in water. H2O, it has an octet of electrons in the outer shell, two shared pairs and two line pairs.

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If another hydrogen ion comes along and shares one of the lone pairs, the oxygen is left with three bonding pairs and one lone pair. Overall, it has possession of only 7 electrons to balance the 8 protons in the nucleus, therefore it now has a positive charge.

Name:  H3O+.png
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Qxi.xli
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(Original post by charco)
Oxygen is element number 8. It has eight electrons.
There are two electrons in the first shell and six in the second shell. (2,6)

Every time it makes a bond to hydrogen it shares one electron of its own and one from hydrogen.

Thus in water. H2O, it has an octet of electrons in the outer shell, two shared pairs and two line pairs.

Name:  H2O.png
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If another hydrogen ion comes along and shares one of the lone pairs, the oxygen is left with three bonding pairs and one lone pair. Overall, it has possession of only 7 electrons to balance the 8 protons in the nucleus, therefore it now has a positive charge.

Name:  H3O+.png
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thank you so much!
you're really good at explaining
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Qxi.xli
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(Original post by charco)
Overall, it has possession of only 7 electrons to balance the 8 protons in the nucleus, therefore it now has a positive charge.
im so sorry to disturb you again, but i'm just re-reading it and got slightly confused about the very last bit.... overall why doesn't it have possession have 8e-s? as covalent bonds are the sharing of electrons?so 4 covalent bonds so it has 8 electrons?
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(Original post by vix.xvi)
im so sorry to disturb you again, but i'm just re-reading it and got slightly confused about the very last bit.... overall why doesn't it have possession have 8e-s? as covalent bonds are the sharing of electrons?so 4 covalent bonds so it has 8 electrons?
It shares each bonding pair and 100% owns each lone pair.
ownership
3 bonding pairs = 3 electrons
1 bonding pair = 2 electrons
2 inner shell electrons
------------------------------------ total
7 electrons and 8 protons, hence it has a positive charge
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