Chemistry Foundations

3.1.2 - Sizes of Atoms, Ions and Nuclei

# Sizes of Atoms, Ions and Nuclei

Although atoms, ions and nuclei are larger than the protons, neutrons and electrons that they are made of, they are still very small.

The size of an atom or ion is usually described by saying what its radius is. The radius is the distance from the centre to the outer edge.

The radius of a typical atom or ion is roughly 0.1nm (nm stands for nanometres). One nanometre is 10-9 metres (0.000000001m) meaning that in metres the radius of an atom or ion is roughly 10-10m. Written out in full that is 0.0000000001m. The exact size varies between different atoms and ions.

The radius of an atom or ion (the distance from the centre to the outer edge) is usually about 0.1nm.

## The radius of a nucleus is about 100,000 times smaller than the radius of an atom or ion

The nucleus is much, much smaller than the whole atom or ion. The radius of a nucleus is around 10-15m (0.000000000000001m), which makes it about 100,000 times smaller than the radius of the whole atom or ion.

## Atoms and ions are mostly empty space

What this means is that the nucleus only takes up a tiny amount of space in the centre of the atom or ion. This is because there is actually a huge amount of space between the nucleus and the electrons (or at least huge compared to the size of the nucleus). Most of the atom or ion is just this empty space.

It can be easier to picture how small the nucleus is if you scale the whole thing up. If the whole atom or ion was the size of a sports stadium then the nucleus would be about the size of a single grain of sand.

## Atoms and ions are not drawn to scale

The diagrams of atoms and ions in this course do not accurately show the amount of space between the nucleus and the electrons. In these diagrams the nucleus is shown taking up much more space than it really does. The reason they have been drawn like this is that in order to accurately show the amount of space between the nucleus and the electrons, either the nucleus would have to be drawn so small that you wouldn’t be able to see it, or the whole atom/ion would have to be so big that it wouldn’t fit on the page.

## Flashcards

Flashcards help you memorise information quickly. Copy each question onto its own flashcard and then write the answer on the other side. Testing yourself on these regularly will enable you to learn much more quickly than just reading and making notes.

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What is the radius of a typical atom or ion (in nanometres)?

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How does the radius of a nucleus compare to the radius of an atom or ion?