Final answer:
The atomic number (Z) represents the number of protons, defining the element, while the mass number (A) is the sum of protons and neutrons, indicating the total nucleons in an atom. Isotopes of elements differ by the number of neutrons, contributing to variations in mass number. The atomic mass is the average of an element's isotope mass numbers and is often displayed in the periodic table.
Step-by-step explanation:
The atomic number (Z) and mass number (A) are fundamental concepts used to characterize the different elements and their isotopes. The atomic number, Z, is the number of protons in the nucleus of an atom and is unique to each element. For example, every oxygen atom has an atomic number of 8. The mass number, A, is the total number of protons and neutrons, also known as nucleons, within the nucleus of an atom. This is illustrated by the fact that while all carbon atoms have an atomic number of 6, the most common carbon isotope has a mass number of 12, due to its six neutrons.
Isotopes are forms of an element that have the same number of protons but a different number of neutrons. The atomic mass is a weighted average of the mass numbers of an element’s naturally occurring isotopes. For instance, the atomic mass of chlorine is 35.45 because it is made up of isotopes with mass numbers of 35 and 37. The periodic table provides insight into these values, typically showing the atomic number above the element's symbol and the atomic mass below it, in each square.
Understanding these concepts helps us to differentiate not just between different elements, but also between different isotopes of the same element, based on their mass number. In essence, the number of neutrons in an element can be calculated by subtracting the atomic number from the mass number.