Have the same number of protons but a different number of neutrons
The elements in nature have several types of isotopes
Isotopes are atoms whose no-atom has the same number of protons while still having a different number of neutrons.
So Isotopes are elements that have the same Atomic Number (Proton)
SO the Three Common Isotopes Of Oxygen :
₈¹⁶O, ₈¹⁷O, and ₈¹⁸O have :
1. The same number of protons = atomic number = 8
2. Have a different number of neutrons :(neutrons= mass number-atomic number)
₈¹⁶O : neutron = 16-8=8
₈¹⁷O : neutron = 17-8=9
₈¹⁸O : neutron = 18-8=10