Name: Structure of Ionic Compounds
Uploaded: 2019-07-19
Duration: 1 min 41 s
Description: We all use salt in our food, as a taste enhancer. But do you know its structure? Want to learn more about it? Watch this interesting video to know the struct...

Question

Draw the structures of $CsCl$ and ${TiO}_{2}$ , showing clearly the coordination of the cations and anions. Show how the Born-Haber cycle may be used to estimate the enthalpy of the hypothetical reaction:

$Ca (s) + \frac{1}{2} {Cl}_{2} (g) \to CaCl (s)$

Explain why $CaCl (s)$ has never been made even though the enthalpy for this reaction is negative.

Accepted Answer

$CsCl$ has $BCC$ structure with co-ordination number $8 : 8$ , it means each ${Cs}^{+}$ is surrounded by $8 {Cl}^{-}$ and each ${Cl}^{-}$ is surrounded by $8 {Cs}^{+}$ ions.

Lattice structure of caesium chloride is following

${TiO}_{2}$ exists in three forms called anatase, brookite and rutile. The rutile structure is most common.

In rutile each ${Ti}^{+ 4}$ ion is octahedrally surrounded by six $O^{- 2}$ ions whereas each $O^{- 2}$ ion is surrounded by only three ${Ti}^{+ 4}$ ions arranged at the three corners of a plane triangle.

The co-ordination numbers of ${Ti}^{+ 4}$ and $O^{- 2}$ ions are $6$ and $3$ , respectively.

So formula ${Ti}_{3}^{+ 4} O_{6}^{- 2}$ or $2 {TiO}_{2}$

Lattice structure of rutile is following

Born-Haber cycle,

Born-Haber cycle is used to analyse reaction energies by applying Hess's law.

$Ca (s) + \frac{1}{2} {Cl}_{2} (g) \to CaCl (s)$

${(I.E.)}_{1} : First ionisation energy {(B.D.E.)}_{Cl-Cl} : Bond dissociation energy of Cl-Cl {∆H}_{eg} : Electron gain enthalpy {∆H}_{f} : Enthalpy of formation$

$Ca$ is stable when it made $+ 2$ ion $([Ar] 4 s^{0})$ instead of in mono positive $(+ 1)$ form $([Ar] 4 s^{1})$ .

That is why, $CaCl (s)$ has never been made even though the enthalpy for this reaction is negative.

Important Questions on The Ionic Bond

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