Are all atoms the same size?

18 June 2019

ATOM-CARTOON

Atom cartoon

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Question

Is an atom always the same size? With something as dense as gold, or as gaseous as helium?

Answer

Chris - Sure. Well this sounds like one for Colm to answer. How big are atoms? Les is saying are they all the same size? Presumably not.

Colm - So Les all atoms of the same material are the same size but different items of different materials are different sizes. So for instance the single smallest item is hydrogen and a single hydrogen is about one twentieth of a nanometre across.

Chris - How big is a nanometre?

Colm - So a nanometre is one billionth of a metre. So, to give you an example, if you take a hair - so a hair is about 50,000 nanometres across - the distance between atoms in a typical material is about a quarter of a nanometre, and the size of a hydrogen atom is about one twentieth of a nanometre. Then, if you go up to something like gold, so gold is about one tenth of a nanometre at its outer radius. But all gold atoms are the same. All hydrogen atoms are the same.

Chris - So, in summary then, all atoms of a type - or one specific element - are the same size, but, because there are nearly a hundred and twenty different elements, there's 120 atoms of different sizes?

Colm - Right!

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