Changing the number of would change an atom into an atom of a different element. changing the number of would change an atom into an atom of a different element. electrons circling the nucleus of an atom protons in an atom particles in the nucleus of an atom bonds formed by an atom neutrons in an atom

Protons

WHY?
Changing electrons will only result in the same element having different charges and hence, changing it's chemical properties.

Changing neutrons will not change an element but it will result in an isotope forming instead. (Isotopes are elements of the same type with different neutron numbers.)

However, changing the proton number would immediately change the nucleus composition, resulting in a change in element with a negative charge as there are more electrons than protons. This results in a expansion in valance electrons's distance from the nucleus. This results in a change in chemical properties of the element.

Therefore, a change in Protons is the answer.