Caesium

[hairygrape]

Our daughter came home from school with a question from her chemistry teacher that seems not straightforward to answer. It's quite simple: What colour is the element Caesium? Can anyone help with the answer please?

[Old_Geezer]

Silvery golden.

[bookbinder]

https://chemistry.stackexchange.com/questions/157812/what-is-the-colour-of-cesium

[teacher1]

silvery-golden

[elliemay1]

//Caesium is a soft, gold-coloured metal that is quickly attacked by air and reacts explosively in water.//

[bobbinwales]

Or sometimes described as pale gold

[elliemay1]

When heated it is blue/violet

[nescio]

Of all the metallic elements, caesium, gold and copper are the only ones which are not silver/grey/white

[theprof]

This question was often asked by tutors to potential undergraduates in Natural Sciences/Chemistry at both Oxford and Cambridge. I suspect the Chemistry teacher was a graduate of one or even both.

I'd be interested to see further opinions.

[elliemay1]

Is it one of those trick qns where the answer is that colour doesn't actually exist and is an illusion??

[theprof]

No ellimay1. It does have a colour.

[elliemay1]

The prof can you please put us out of our misery!

[theprof]

Sorry elliemay1. It's actually silvery-white in colour. This can be confirmed by reference to Hawley's Chemical Dictionary, Perry's Handbook of Inorganic Compounds and numerous other academic reference sources available online. The likes of Wikipedia etc fail to tell the whole story; Britannica refers to it as a "silvery metal with a golden cast" which is a start I suppose.
The reason it appears "brassy" in colour (not golden) is because of the properties of the alkali metals in the Periodic Table. As we move down the metals in Group 1, the frequency of light needed to excite electrons decreases. The frequencies for Lithium, Sodium, Potassium and Rubidium are in the ultraviolet spectrum but thr Caesium frequency is in the blue-violet end of the visible spectrum. Blue-violet is thus absorbed by the element whilst other colours are reflected, as they are of lower frequency. These reflected colours come together to make up the golden colour of the element we see.
Whilst some of this may appear to be pedantic, there are situations where the silvery-white colour becomes evident; during Caesium distillation ( banned in all uk academic institutions due to the almost certainty of an explosion), Caesium looks like Mercury with no trace of the golden colour. There are other situations where the same applies

[theprof]

A quick look online shows that the texts on Credo Reference and Oxford Reference all seem to confirm that Caesium is silvery- white in colour. These are resources used by school children almost daily and may add some credence when hairygrape's daughter's discusses it with her chemistry teacher.

[mibn2cweus]

Just to add to the confusion the name caesium was coined from the Latin term 'ceasius' meaning sky-blue.