Here's why:

* Atomic Structure: Atoms are made up of a central nucleus containing positively charged protons and neutral neutrons. Surrounding the nucleus is a cloud of negatively charged electrons.

* Electrons in the Shell: The electrons occupy specific energy levels or "shells" around the nucleus. The number of electrons in each shell determines the atom's chemical properties.

* Charge: Electrons carry a negative charge, while protons carry a positive charge. The attraction between these opposite charges keeps the electrons bound to the atom.

Let me know if you'd like more information about atomic structure or the role of electrons in chemical bonding!