Atoms of each element consist of a particular number of protons. In fact, the number of protons dictates what atom we are looking at (e.g., all atoms with 6 protons are carbon atoms). Atomic number is the number of protons there in an atom. On the other hand, the number of neutrons for a given element can differ. Together, the number of protons and the number of neutrons dictates an element’s mass number.
The atomic number (expressed by the letter Z) of an element is the number of protons in the nucleus of each atom of that element. An atom can be classified as an element based exclusively on its atomic number. For instance, an atom with an atomic number of eight (its nucleus contains 8 protons) is an oxygen atom, and an atom with a different number of protons would be a different element. The periodic table is set in an order of increasing atomic number.
An element’s mass number (A) is the total of the number of protons and the number of neutrons. The small role of mass from electrons is overlooked in calculating the mass number. This approximation of mass can be used to easily determine how many neutrons an element has by simply deducting the number of protons from the mass number. Isotopes of the same element will have a similar atomic number but different mass numbers.
Atomic Number: The number of protons present in an atom is known as Atomic number.
Atomic Number: The atomic number of an atom is not affected by the number of neutrons.