How are isotopes identified in the periodic table?

Isotopes are identified in the periodic table by their atomic number and mass number.

In the periodic table, each element is represented by its atomic number and atomic mass. The atomic number, which is the number of protons in an atom, identifies the element. For example, all atoms with 6 protons are carbon atoms. However, atoms of the same element can have different numbers of neutrons. These variations are called isotopes.

Isotopes of an element have the same atomic number but different mass numbers. The mass number is the total number of protons and neutrons in an atom. For example, carbon-12 and carbon-14 are both isotopes of carbon. They both have 6 protons (so their atomic number is 6), but carbon-12 has 6 neutrons while carbon-14 has 8 neutrons. This gives them different mass numbers: 12 and 14 respectively.

In the periodic table, the atomic mass listed for each element is actually a weighted average of the masses of its isotopes, taking into account how common each isotope is. This is why the atomic mass is usually not a whole number. For example, the atomic mass of carbon is listed as approximately 12.01, not 12, because it reflects the slight contribution of the heavier carbon-14 isotope.

To identify a specific isotope in the periodic table, you need to know both its atomic number (which identifies the element) and its mass number (which identifies the isotope). For example, to identify carbon-14, you would look for the element with atomic number 6 (carbon) and then consider the isotope with mass number 14.