Why is nano particle of gold red

[Priority]

Why is nano particle of gold red? Like if gold gets cut down to nanometre size , the colour of it becomes red.why?

[shezz.iazz]

Hi,

The color of any bulk form material such as Gold in this case will be different to the color of the same material in nanoparticle form. Why? that's because as you break a bulk form material down into a smaller particle, the physical, chemical and optical properties change. So gold can be found in many different colors, the color depends on the size of the particle. i'll give you an example if this is still not clear. There is a Birthday Cake, you cut a piece out and it is still the same cake with the same color and taste. However particles function differently, it is something you just have to go with.

Hope this helped

[sarangiya]

I think shezz.iazz's answer is correct but perhaps to elaborate a bit:

The colour changes in nanogold reflect the size of the nanoparticles. Even different sizes of nanogold exist and so the colour can vary from a strong red to a deep purple, or even orange or blue etc.
The Jacaranda Chemistry 1 textbook has a good picture illustrating this:


The reason the size of the particle matters is because of nanoparticles are so small that they will absorb and reflect some parts of the visible spectrum and not others (unlike bulk gold nugs). There's some complex surface plasmon resonance you could google but my very basic understanding of it is that basically the electrons of the nanoparticles will resonate or move at a certain wavelength of the visible spectrum instead of reflecting it all like opaque gold nug.
Apparently the red appears when the gold is 30nm in diameter, and goes orange at 80nm.

Hope that satisfies anyone who was wondering why size matters (lol)