Here's why:
* Atomic Number: Each element is defined by its atomic number, which represents the number of protons in its nucleus.
* Protons and Neutrons: Protons and neutrons make up almost all of an atom's mass.
* Isotopes: Most elements have isotopes, which are atoms of the same element with different numbers of neutrons. This means their atomic masses can vary.
Example:
* Carbon has an atomic number of 6, meaning it always has 6 protons.
* Carbon-12 has 6 neutrons, making its atomic mass 12.
* Carbon-14 has 8 neutrons, making its atomic mass 14.
Conclusion:
The periodic table lists the average atomic mass of each element, taking into account the natural abundance of its isotopes. While elements share the same number of protons, their masses can vary due to the presence of isotopes.
