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Chemicals properties of an atom are mainly influenced by its electrons. Specifically, it's the electrons in the outermost shell, also called valence electrons, that play a crucial role in determining how the atom reacts chemically with others.
Since isotopes of the same element have the same number of electrons and the same arrangement of these electrons, called electron configuration, their chemical properties remain identical. This is why isotopes, despite having different atomic masses, usually exhibit the same kind of reactions and bonding behaviors.
Therefore, even though isotopes differ in the number of neutrons in the nucleus, this does not affect chemical properties because it's the distribution and number of electrons that are the defining factors in chemistry.

Atoms of the same element can have different numbers of neutrons, and this changes their atomic mass. The atomic mass of an isotope is the sum of protons and neutrons in the nucleus.
Because isotopes have different numbers of neutrons, they will have different atomic masses. This is why when you look at the periodic table, the atomic mass listed is often a decimal. It represents an average atomic mass considering all the naturally occurring isotopes of that element and their relative abundances.
For example, carbon has isotopes with atomic masses of approximately 12 and 14, due to the presence of 6 protons and either 6 or 8 neutrons respectively. When calculating atomic mass, scientists take into account all such isotopes.

The electron configuration of an atom refers to the arrangement of electrons in different energy levels around the nucleus. This configuration determines many physical and chemical properties of the element.
Isotopes of the same element have nearly identical electron configurations because they possess the same number of protons and electrons. This results in electrons being arranged in comparable ways across these isotopes.
Identical electron configurations mean isotopes have similar chemical behavior despite differences in atomic mass. For example, all the isotopes of hydrogen have a single electron surrounding the nucleus, leading to virtually the same electron configuration.

• This consistency in electron arrangement ensures isotopes do not alter their fundamental chemical nature due to changes in neutron count.
  
• The lack of influence of neutron variation on electron distribution underscores why isotopes remain chemically similar.