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How do the numbers of electrons compare in two isotopes of an element?

Isotopes are atoms of an element that have the same atomic number, but different atomic masses. For example, U-235 and U-238 are two isotopes of the element uranium. They have the same atomic number (92), but different mass numbers (235 and 238). The atomic number is the same as the number of protons. 


Thus, the number of protons of uranium = atomic number of uranium = 92.


The mass number is the sum total of number of protons and neutrons.


Thus, number of neutron = mass number - number of protons


= 235 - 92 = 143


and, 238 - 92 = 146.


Thus, the isotopes have same number of protons, but different numbers of neutrons.


Since the number of electrons is equal to the number of protons for an atom in the ground state, the number of electrons will be equal for all the isotopes of an element (for example, for the two isotopes of uranium, the number of electrons is 92).


Thus, the isotopes of an element differ only in terms of the number of neutrons and not in terms of the number of protons or electrons. 


Hope this helps.

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