When we talk about atomic number, mass number, and isotopes, it’s important to know what each of these terms means. Let’s break them down:

1. Atomic Number (Z)
   This is the number of protons found in an atom's center, known as the nucleus. The atomic number tells us what kind of element it is.
   For example, carbon has an atomic number of 6. This means carbon has 6 protons.
   The atomic number also shows where the element is in the periodic table.

2. Mass Number (A)
   The mass number is the total count of protons and neutrons in the nucleus of an atom.
   Let’s look at carbon again. The most common type of carbon is called carbon-12. It has 6 protons and 6 neutrons.
   So, its mass number is A = 6 + 6 = 12.

3. Isotopes
   Isotopes are different versions of the same element that have a different number of neutrons.
   For carbon, besides carbon-12, there is also carbon-14. This type has 6 protons and 8 neutrons.
   So, its mass number is A = 6 + 8 = 14.

In short, the atomic number tells us what element we have, the mass number tells us the total number of protons and neutrons, and isotopes are different forms of an element that have different amounts of neutrons.