How do the atoms of different chemical elements differ from each other?

The atoms of various chemical elements differ:
– the number of protons in the nucleus;
– the number of electrons in the electron shell surrounding the nucleus. In normal state
(not ionized) the number of electrons is equal to the number of protons in the nucleus.
Atoms of one chemical element can have several varieties (isotopes), differing only in the number of neutrons in the atomic nucleus. Isotopes have similar physical and chemical properties.

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