[ptcl4]2- reason behind its colour

The colour of a complex ion such as [PtCl4]2- is due to the absorption of certain wavelengths of light by the d-electrons of the central metal atom, platinum in this case. This absorption of light causes an electron to be promoted from a lower energy d-orbital to a higher energy d-orbital. The remaining wavelengths of light are then transmitted or reflected, and this is the colour that we see.

The specific colour observed depends on the difference in energy between the d-orbitals, which is influenced by several factors:

1. The identity of the central metal atom: Different metals have different electron configurations, and thus different energy gaps between their d-orbitals.

2. The oxidation state of the metal: The charge on the metal can affect the energy levels of the d-orbitals.

3. The identity of the ligands: Different ligands can cause different amounts of splitting of the d-orbitals.

4. The geometry of the complex: The arrangement of the ligands around the central metal atom can also affect the splitting of the d-orbitals.

In the case of [PtCl4]2-, the specific combination of platinum and chloride ions results in a complex that absorbs and reflects light in a way that gives it its particular colour.