Explain atomic structure and the shells part?

Atoms are
the smallest unit of matter. They are comprised of (made of) three subatomic particles -
protons, neutrons, and electrons. Protons are positively charged, neutrons are neutral (have
neither positive nor negative charge), and electrons are negatively charged. The protons and
neutrons are housed within the central nucleus of an atom. Thus, the overall charge of the
nucleus is positive. The negative electrons travel around the nucleus. Some scientists claim the
electrons...

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