An atom of an element with a different number of neutrons is called an isotope. Isotopes are atoms of the same element that have the same number of protons (and hence the same atomic number) but differ in the number of neutrons, leading to different atomic masses.
For example, let's consider the element carbon. A typical carbon atom has 6 protons, 6 electrons, and 6 neutrons, giving it an atomic mass of approximately 12 atomic mass units (amu). However, carbon also has isotopes with different numbers of neutrons. Carbon-13 (¹³C) has 6 protons, 6 electrons, and 7 neutrons, resulting in an atomic mass of approximately 13 amu. Carbon-14 (¹⁴C) has 6 protons, 6 electrons, and 8 neutrons, with an atomic mass of approximately 14 amu.
These isotopes of carbon have slightly different atomic masses due to the varying number of neutrons. Isotopes may exhibit slightly different physical properties, such as different nuclear stabilities or radioactive decay rates. They can also have applications in fields like radiocarbon dating, medical imaging, and nuclear medicine.
It's worth noting that while isotopes have different numbers of neutrons, they still belong to the same element because they have the same number of protons, which determines the element's identity and chemical behavior.