Final answer:
The atomic number, which equals the number of protons, identifies an element and indicates the number of electrons in a neutral atom. The number of neutrons can be found by subtracting the atomic number from the mass number. Isotopes have the same number of protons but differ in the number of neutrons.
Step-by-step explanation:
The number of protons in the nucleus of an atom is known as the atomic number, and it's a unique identifier for each element. Specifically, the number of protons determines the type of element an atom represents. For instance, an atom with six protons is always a carbon atom. In an electrically neutral atom, the number of protons equals the number of electrons. This means that the atomic number also reveals how many electrons the atom has.
The combined total of protons and neutrons is known as the mass number of an atom. You can calculate the number of neutrons in an atom by subtracting the atomic number from the mass number (A - Z = number of neutrons). This is crucial because it affects the atom's mass and the creation of different isotopes, which are atoms of the same element that vary in the number of neutrons.
When discussing an atom's mass, it's important to note that scientists often refer to the atomic mass, which is a weighted average of all naturally occurring isotopes, taking into account their relative abundance. This atomic mass can include decimals, as seen with elements like chlorine, which has an atomic mass of 35.45 due to a mix of isotopes.