Definition
The total count of protons and neutrons within an atom's nucleus.
质量数
The mass number of carbon-12 is 12, indicating it has 6 protons and 6 neutrons.
碳-12的质量数是12，表示它有6个质子和6个中子。
To calculate an atom's mass number, you must add up the number of protons and neutrons in its nucleus.
要计算原子的质量数，你必须将原子核中的质子和中子数量相加。
Isotopes have different mass numbers due to variations in their neutron count.
同位素的质量数不同，因为它们的中子数量有所变化。