Atoms are the smallest pieces of matter. They are the tiniest particles into which a substance can be divided without changing into something else. Atoms actually consist almost entirely of open space, in which tiny particles orbit the central particle, or nucleus. The particles travel so fast that they seem to be solid.
Atoms are so tiny that the smallest particle visible to the naked eye would contain about one million billion atoms. Despite their tiny size, atoms can be seen individually under very powerful electron microscopes.
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