[arvin_infinity]

Apparently they are not the same thing and not interchangeable ..wondered if someone can clarify on that!


E.g. Charge density for Mg 2+ is higher than charge d. for Ca 2+


+rep

[thegodofgod]

(Original post by arvin_infinity)
Apparently they are not the same thing and not interchangeable ..wondered if someone can clarify on that!


E.g. Charge density for Mg 2+ is higher than charge d. for Ca 2+


+rep

Electron density is specific for electrons, e.g. electron density in a C=C bond is high.

Charge density is more related to nuclear charge, I think, e.g. Fe³⁺ has a greater charge density than that of Fe²⁺, as Fe³⁺ has a smaller ionic radius due to greater effective nuclear charge than Fe²⁺.

The charge density for Mg²⁺ is higher than that of Ca²⁺, as Mg²⁺ is a smaller ion, as it has one fewer energy level.

[arvin_infinity]

(Original post by thegodofgod)
Electron density is specific for electrons, e.g. electron density in a C=C bond is high.

Charge density is more related to nuclear charge, I think, e.g. Fe³⁺ has a greater charge density than that of Fe²⁺, as Fe³⁺ has a smaller ionic radius due to greater effective nuclear charge than Fe²⁺.

The charge density for Mg²⁺ is higher than that of Ca²⁺, as Mg²⁺ is a smaller ion, as it has one fewer energy level.

Good one!
Speaking of e density - electron density in benzene ring is lower than c=c?

[illusionz]

(Original post by arvin_infinity)
Good one!
Speaking of e density - electron density in benzene ring is lower than c=c?

In terms of pi electron density, I don't think so. You have 6 electrons delocalised over 6 carbons, which is one electron per carbon. A C=C bond has 2 electrons shared between 2 carbons, which is also 1 electron per carbon. The difference is that each of the bond orders is 1.5, whereas in an alkene you have bond orders of 1 and 2 depending on whether it's a single or double bond.

There is a property known as population, which is basically the number of electrons on each carbon atom of a polyene. It can be shown using more advanced chemistry than you know that the population for any linear molecule or chain with an even number of atoms in the ground state has 1 electron per atom in the pi system.

[thegodofgod]

(Original post by illusionz)
Nope. You have 6 electrons delocalised over 6 carbons, which is one electron per carbon. A C=C bond has 2 electrons shared between 2 carbons, which is also 1 electron per carbon.

There is a property known as population, which is basically the number of electrons on each carbon atom of a polyene. It can be shown using more advanced chemistry than you know that the population for any linear molecule or chain with an even number of atoms in the ground state has 1 electron per atom in the pi system.

Am I being really thick today, or does a C=C bond have 4 electrons within it?

[illusionz]

(Original post by thegodofgod)
Am I being really thick today, or does a C=C bond have 4 electrons within it?

I was talking in terms of the pi electron density, which is what matters from a reactivity point of view. I can see your confusion.

[thegodofgod]

(Original post by illusionz)
I was talking in terms of the pi electron density, which is what matters from a reactivity point of view. I can see your confusion.

Ahh, so the 2 sigma bond electrons don't count?

[illusionz]

(Original post by thegodofgod)
Ahh, so the 2 sigma bond electrons don't count?

I have no idea what your A level exams want you to say. They matter in terms of counting absolute electron density, but in all the theoretical stuff I've done the last two years you only consider pi electron density because the pi bonds are the ones involved in reactions.

[thegodofgod]

(Original post by illusionz)
I have no idea what your A level exams want you to say. They matter in terms of counting absolute electron density, but in all the theoretical stuff I've done the last two years you only consider pi electron density because the pi bonds are the ones involved in reactions.

All we need to know for the exam is that C=C bonds have a high electron density, and thus they undergo electrophilic addition

But I do have to admit, the sigma / pi bond stuff confuses the hell out of me

[arvin_infinity]

(Original post by thegodofgod)
All we need to know for the exam is that C=C bonds have a high electron density, and thus they undergo electrophilic addition

But I do have to admit, the sigma / pi bond stuff confuses the hell out of me

So now I understand that they are not the same thing! and when to use which..

Here is another one: any difference between lone pair and pair of electrons?

[thegodofgod]

(Original post by arvin_infinity)
So now I understand that they are not the same thing! and when to use which..

Here is another one: any difference between lone pair and pair of electrons?

Yes, a subtle difference - a lone pair of electrons is one which is not involved in bonding; a pair of electrons can be a lone pair of electrons, or a pair of electrons which is involved in a covalent bond.

For example, in a water molecule, the oxygen atom has 2 lone pairs of electrons and 2 bond pairs of electrons, giving it a bond angle of 104.5^o

[arvin_infinity]

(Original post by thegodofgod)
Yes, a subtle difference - a lone pair of electrons is one which is not involved in bonding; a pair of electrons can be a lone pair of electrons, or a pair of electrons which is involved in a covalent bond.

For example, in a water molecule, the oxygen atom has 2 lone pairs of electrons and 2 bond pairs of electrons, giving it a bond angle of 104.5^o

+rep finally after agesss

So if I define ligands by saying "a molecule or ion that donates a lone pair .."
it will be just non-sense and probably I lose a mark!

[tdx]

(Original post by arvin_infinity)
+rep finally after agesss

So if I define ligands by saying "a molecule or ion that donates a lone pair .."
it will be just non-sense and probably I lose a mark!

I believe that would be correct, it has a lone pair, which it donates to a central metal ion to form a dative covalent bond! correct me if I'm wrong

[tdx]

(Original post by arvin_infinity)
+rep finally after agesss

So if I define ligands by saying "a molecule or ion that donates a lone pair .."
it will be just non-sense and probably I lose a mark!

when I say your correct I believe you will get the mark