Final answer:
The change in the number of electrons in an atom results in the formation of ions, altering the atom's charge and affecting its chemical reactivity and physical properties, but does not change its elemental identity.
Step-by-step explanation:
Changing the number of electrons in an atom affects the atom's charge, transforming it into an ion. A neutral atom has an equal number of protons and electrons. When you add electrons to an atom, it becomes a negatively charged ion, and when you remove electrons, it becomes a positively charged ion. For example, when a sodium atom loses one electron, it becomes a positively charged sodium ion (Na+), and a chlorine atom that gains an electron becomes a negatively charged chloride ion (Cl-). These changes influence the chemical reactivity and physical properties of the atom, such as size, ionization energies, and electron affinities, but the type of atom, defined by its number of protons, remains the same.