colours of ions (aqueous)

1. What are the colours of oxide ions and carbonate ions in aqueoussolution?

In aqueous solution, oxide ions do not exist. In aqueous solution, oxide ions will react with water to give hydroxideions.
O^2- + H2O → 2OH^-
Oxide ions can only exist in solid form or in complexes.

In aqueous solution, carbonate ions are colourless.


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2. If oxide ions are colourless, then why is copper(II) oxide black but notblue?

In aqueous solution, copper(II) ions exist as [Cu(H2O)n]^2+,which responsible for the blue colour. The energy levels of copper(II) ion are affected by the H2Omolecules (ligands) surrounding it.

In solid copper(II) oxide, copper(II) ions are surrounded by oxide ions. Theenergy levels of copper(II) ion are affected by the oxide ions surrounding it.

In the above two cases, the energy levels of copper(II) ion are different. Therefore, they absorb different wavelengthsof light and show different colours.


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3. Are there any simple ways to determine the colours of ionic compounds?

No.
One can only determine the colours of aqueous solutions of ionic compounds.


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There are no cations and anions in covalent bonding, then what particles causethe colours of covalent compounds?

The colour is due to bonding electrons absorb energy to transit themselves fromlow energy levels of the covalent bonds to high energy levels.