What is an atom?

Quick explanation

An atom is the smallest component constituting a chemical element.

Atoms comprise (up to) three different particles: In the center is the nucleus, consisting of a number of positively charged protons, and a roughly similar number of neutral neutrons.

Around the nucleus is (usually) a cloud of electrons, which can be thought of as orbiting the nucleus like planets around a star.

The number of protons specifies which element it is; for instance, hydrogen has one proton, oxygen has eight protons, and uranium has 92 protons.

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