No, not every atom of an element has the same number of nucleons. An element is defined by the number of protons in its nucleus, which determines its atomic number and gives the element its unique identity. For example, all carbon atoms have six protons, and all oxygen atoms have eight protons.
However, the number of neutrons in the nucleus can vary among atoms of the same element. Atoms of the same element with different numbers of neutrons are called isotopes. Isotopes have the same atomic number (number of protons) but differ in their mass number, which is the sum of protons and neutrons.
Isotopes of an element have nearly identical chemical properties because they have the same number of protons, which determines the element's chemical behavior. However, isotopes may have slightly different physical properties due to variations in their mass and nuclear stability.
For example, carbon-12 (12C) has six protons and six neutrons, while carbon-13 (13C) has six protons and seven neutrons. Both isotopes are carbon, but they differ in their atomic mass. Carbon-12 is the most abundant isotope of carbon, while carbon-13 is a less common, stable isotope.
The existence of isotopes allows for variations in the number of neutrons in the nucleus, providing different mass variants of an element while maintaining its chemical identity.