The mass number of an atom is determined by adding the number of protons and neutrons in its nucleus. It's a simple calculation, but understanding its significance is key. The mass number isn't directly measured; instead, it's calculated based on the element's atomic number (number of protons) and the number of neutrons.
For example, carbon has an atomic number of 6, meaning it has 6 protons. A common isotope of carbon, carbon-12, has 6 neutrons. Therefore, its mass number is 12 (6 protons + 6 neutrons).
It's important to note that the mass number represents the total number of protons and neutrons, and it doesn't directly correspond to the atom's actual mass. The actual mass of an atom is influenced by the binding energy of its nucleus, which is a more complex concept.
However, for most practical purposes, the mass number provides a good approximation of an atom's relative mass.
In summary:
- Mass number = Number of protons + Number of neutrons
- It's a calculated value, not a directly measured one.
- It gives a rough estimate of an atom's relative mass.
Practical applications:
- Identifying isotopes: Isotopes of the same element have the same number of protons but different numbers of neutrons, leading to different mass numbers.
- Understanding nuclear reactions: The mass number changes during nuclear reactions like radioactive decay, providing information about the transformation of atoms.
Recent advancements:
- FIONA (Facility for Isotopic and Nuclear Analysis) at Berkeley Lab enables the direct measurement of the mass number of superheavy elements.
