Final answer:
In atomic notation, the number of protons is indicated by the atomic number, placed as the lower left subscript next to the element's symbol. This number defines the element and, in a neutral atom, also the number of electrons.
Step-by-step explanation:
The number of protons in an atom is represented in atomic notation as the atomic number, and is positioned as the lower left subscript of the element symbol. For example, including the number of protons, neutrons, and electrons for sodium in standard notation, we would write 2311Na, where the atomic number 11 (the subscript) represents the number of protons (and also the number of electrons in a neutral atom), and the mass number 23 (the superscript) represents the total number of protons and neutrons.
Every element has a unique number of protons that defines it, which is why the atomic number is so crucial. For instance, hydrogen has an atomic number of 1, indicating it has one proton, while gold has an atomic number of 79, signifying it has 79 protons. Isotopes are variations of an element that have the same number of protons but different numbers of neutrons and are indicated by the mass number. For example, carbon-12 (where 12 is the mass number denoting the sum of 6 protons and 6 neutrons for the most common isotope of carbon