How can one describe aluminum monochloride cation with a covalency model?

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How can one describe aluminum monochloride cation with a covalency model?

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Answer 1 · 2017-09-09T14:56:22

This is representable as

${AlCl}^{2 +}$ $"AlCl"^(2+)$

in aqueous solution.

The water molecules are just interacting electrostatically, and not actually bonding.

Their partially negative end is pulled by aluminum's $+ 3$ $+3$ oxidation state in an ion-dipole interaction.
${Cl}^{-}$ $"Cl"^(-)$ is similarly pulled by $Al$ $"Al"$ 's $+ 3$ $+3$ oxidation state.

These are good approximations because ${AlCl}^{2 +}$ $"AlCl"^(2+)$ is very much a diatomic ion with respect to water, and has a nearly ionic bond within itself---the electronegativity difference is $E N_{C l} - E N_{A l} = 3.0 - 1.5 = 1.5$ $EN_(Cl) - EN_(Al) = 3.0 - 1.5 = 1.5$ .

For a two-atom bond that is nearly ionic, the covalency is at best $1$ $1$ since in ${AlCl}^{2 +}$ $"AlCl"^(2+)$ , aluminum at best owns $1$ $1$ valence $3 s$ $3s$ electron as ${Al}^{2 +}$ $"Al"^(2+)$ , and at worst, it owns no $3 s$ $3s$ valence electrons as ${Al}^{3 +}$ $"Al"^(3+)$ . In reality, less than half the electron density is "owned" by $Al$ $"Al"$ atom.

As such, one cannot accurately describe this with covalency as a model.

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How can one describe aluminum monochloride cation with a covalency model?

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