Final answer:
The atomic number on the periodic table represents the number of protons in an atom's nucleus and the number of electrons in a neutral atom. It also defines the element's identity and is indicated above the element's symbol on the periodic table.
Step-by-step explanation:
The atomic number of an element represents two key parts of an atom: the number of protons in the nucleus, and in an electrically neutral atom, the number of electrons surrounding the nucleus. This number is crucial because it defines the identity of the element. For instance, every carbon atom has an atomic number of 6, which means it has 6 protons. The periodic table clearly indicates the atomic number above the symbol for each element and the approximate atomic mass below it. The atomic number is also used in the notation for isotopes, where the mass number (sum of protons and neutrons) appears as a superscript and the atomic number as a subscript next to the element's symbol. However, the atomic number is sometimes omitted since the identity of the element can be determined by its unique symbol.