transition metals

how would you know whether a complex is going to be white or colourless? I know sometimes there might be a full d subshell meaning visible light cant be absorbed but how would you know whether it becomes white or colourless?

Reply 1

TypicalNerd

Original post by Frizzle16523

It is to do with the number of d-electrons.

If the d-subshell is full or empty, the ion should be colourless. You are best off memorising a few examples:

Scandium(III) (empty d-subshell)
Titanium(IV) (empty d-subshell)
Copper(I) (full d-subshell)
Zinc(II) (full d-subshell)
Silver(I) (full d-subshell)

(edited 1 month ago)

Reply 2

Frizzle16523

Original post by TypicalNerd

It is to do with the number of d-electrons.
If the d-subshell is full or empty, the ion should be colourless. You are best off memorising a few examples:
Scandium(III) (empty d-subshell)
Titanium(IV) (empty d-subshell)
Copper(I) (full d-subshell)
Zinc(II) (full d-subshell)
Silver(I) (full d-subshell)

Ah ok so how do we know when it’s white?

Reply 3

TypicalNerd

Original post by Frizzle16523

Ah ok so how do we know when it’s white?

It’s white if it’s a solid rather than a complex ion.

Reply 4

Nitrotoluene

Original post by Frizzle16523

Light and Color Basics

Visible light shows as a rainbow of colors from 400 to 700 nanometers. When a compound absorbs certain wavelengths, we see the colors it doesn’t take in. If it doesn’t absorb any light, it appears:
- Colorless (like water or oxygen).
- White (like sugar or salt, which reflects all light).

Why Are Some Compounds Colorless or White?

Full d-Orbitals
- Metals like zinc (Zn^2+) or silver (Ag^+) have full d-orbitals and can't absorb visible light. So, compounds like ZnSO4 (white powder) or [Ag(NH3)2]^+ (colorless solution) lack color.
- Metals like scandium (Sc^3+) or titanium (Ti^+4) also don’t display color because they have empty d-orbitals, like titanium dioxide (TiO2) found in paints as pigment and sunscreen as chemical filter.

Energy Gaps

Sometimes metals have d-electrons, but the energy needed to move them might be outside the visible range. For example:
- [Ti(H2O)6]^4+ is colorless since it absorbs UV light instead of visible light.
- Some iron(III) compounds appear pale yellow, barely touching visible light.
3. Charge Transfers
Color can also come from electrons moving between metals and ligands. If these movements are in the UV range, the compound stays colorless, like potassium ferrocyanide (K4[Fe(CN)6]).
4. Weak Ligands
- Weak ligands like water (H2O) create small energy gaps, leading to absorption in UV light, making [Zn(H2O)6]^2+ colorless.
- Strong ligands can shift absorption into UV, keeping compounds from being colored.
5. Solids vs. Solutions
- A solid (like MgO or BaSO4) looks white as it reflects all light.
- A solution (like [Ag(NH3)2]^+ in water) is clear, allowing light to pass through.

Real Examples

Colorless/White:
- Zinc sulfate (ZnSO4) – white powder.
- Titanium dioxide (TiO2) – bright white pigment.
- Sodium chloride (NaCl) – table salt.
Colored:
- Copper sulfate (CuSO4) – greenish-blue (absorbs orange light).
- Potassium permanganate (KMnO4) – deep purple (charge transfer in visible range).

Thee Main Point

A compound is colorless or white if:
-Its electrons don't interact with visible light (d^0, d^10, or wrong energy gap).
-There are no charge-transfer effects in the visible range.
-Solids scatter light evenly instead of absorbing it.
Next time you see a white powder or clear liquid, you'll know it's all about what light it doesn’t absorb!😀
My2cents!

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