To understand isotopes, we need to look at two important ideas: atomic number and mass number.

1. Atomic Number (Z):

   • This tells us how many protons are in the center of an atom, called the nucleus.
   • All isotopes of the same element have the same atomic number.

2. Mass Number (A):

   • This is the total count of protons and neutrons in the nucleus.
   • Different isotopes of the same element can have different mass numbers.

3. How We Show Isotopes:

   • We write isotopes using a special format: $_{Z}^{A}X$.
   • For example, Carbon-12 is written as ($^{12}C$), where it has $Z=6$ and $A=12$.
   • Another example is Carbon-14, written as ($^{14}C$). It also has $Z=6$, but its mass number, $A$, is 14.

This way, we can easily identify and compare different isotopes of an element!