What does the mass number of an atom represent?

The mass number of an atom represents the sum of protons and neutrons in its nucleus. Protons and neutrons, collectively known as nucleons, are the primary contributors to the mass of an atom, while electrons have a negligible mass compared to protons and neutrons.

Understanding this concept is critical because the mass number provides insight into the isotopes of an element. Isotopes have the same number of protons (which defines the element) but differ in the number of neutrons, leading to variation in mass numbers. For example, carbon-12 has a mass number of 12, which indicates it has 6 protons and 6 neutrons, while carbon-14, another isotope of carbon, has 6 protons and 8 neutrons, giving it a mass number of 14.

Recognizing the relationship between protons, neutrons, and the mass number is fundamental in chemistry, particularly in understanding atomic structure, reactions, and the behavior of elements in different conditions.