# perfect ionic model help

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#1
For this, if we had obtained a value for lattice enthalpy of formation and the question said Predict whether the magnitude of the lattice enthalpy of formation that you have calculated in part (d) will be less than, equal to or greater than the value that is obtained from a perfect ionic model. Explain your answer, would the answer be "greater than"? if so, how do you work it out? thanks
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2 years ago
#2
(Original post by Bertybassett)
For this, if we had obtained a value for lattice enthalpy of formation and the question said Predict whether the magnitude of the lattice enthalpy of formation that you have calculated in part (d) will be less than, equal to or greater than the value that is obtained from a perfect ionic model. Explain your answer, would the answer be "greater than"? if so, how do you work it out? thanks
The question needs more context. What were parts (a) to (d)?
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#3
the previous part involved calculating a value using born haber cycles
(Original post by charco)
The question needs more context. What were parts (a) to (d)?
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2 years ago
#4
(Original post by Bertybassett)
the previous part involved calculating a value using born haber cycles
I guessed that .... but of what?
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#5
well of the lattice enthalpy of formation. Does covalent character always result in stronger bonds between ions, hence is the value calculated using experimental enthalpies of enthalpy of dissociation and formation greater (compared to just using the perfect ionic model)?
(Original post by charco)
I guessed that .... but of what?
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2 years ago
#6
(Original post by Bertybassett)
well of the lattice enthalpy of formation. Does covalent character always result in stronger bonds between ions, hence is the value calculated using experimental enthalpies of enthalpy of dissociation and formation greater (compared to just using the perfect ionic model)?
Why are you being coy?

Just tell me what the bloody compound is!
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#7
the compound was silver chloride
(Original post by charco)
Why are you being coy?

Just tell me what the bloody compound is!
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2 years ago
#8
(Original post by Bertybassett)
the compound was silver chloride
The experimental lattice enthalpy is greater than the theoretical. This suggests that the ionic model is not perfect and that there is some additional macromolecular covalent character within the lattice that contributes further to the bonding.

You cannot predict this. In some cases covalent character reduces the latticel enthalpy, such as for tin chloride.
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#9
thanks, but the question say predict this.See question 1e on this https://pmt.physicsandmathstutor.com...s%202%20QP.pdf
(Original post by charco)
The experimental lattice enthalpy is greater than the theoretical. This suggests that the ionic model is not perfect and that there is some additional macromolecular covalent character within the lattice that contributes further to the bonding.

You cannot predict this. In some cases covalent character reduces the latticel enthalpy, such as for tin chloride.
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2 years ago
#10
(Original post by Bertybassett)
thanks, but the question say predict this.See question 1e on this https://pmt.physicsandmathstutor.com...s%202%20QP.pdf
It's a sh*t question, because it is not possible to predict the answer. You have to already know that the silveer ion can distort the chloride ion charge cloud and introduce some covalent character to the structure.

BUT, like I said, there are two possible consequences of deviation from a pure ionic model and each gives a different result.

If the ionic distortion gives rise to increased covalent character, this can result in macromolecular behaviour (eg AgCl) or simple covalent behaviour (SnCl2).

The silver ion is small enough to distort the chloride ion charge cloud, but so is the Sn2+ ion.

The empirical evidence is the melting point:

AgCl 455ºC
SnCl2 247ºC

Read through the Chem Guide explanation:

https://www.chemguide.co.uk/physical...s/lattice.html

It won't help..
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#11
ok thanks, so if the bonding is stronger between the ions as a result of covalent character, would this result in the experimental lattice enthalpy of formation and dissociation being greater than the values using the theoretical model using the perfect ionic model?
(Original post by charco)
It's a sh*t question, because it is not possible to predict the answer. You have to already know that the silveer ion can distort the chloride ion charge cloud and introduce some covalent character to the structure.

BUT, like I said, there are two possible consequences of deviation from a pure ionic model and each gives a different result.

If the ionic distortion gives rise to increased covalent character, this can result in macromolecular behaviour (eg AgCl) or simple covalent behaviour (SnCl2).

The silver ion is small enough to distort the chloride ion charge cloud, but so is the Sn2+ ion.

The empirical evidence is the melting point:

AgCl 455ºC
SnCl2 247ºC

Read through the Chem Guide explanation:

https://www.chemguide.co.uk/physical...s/lattice.html

It won't help..
0
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