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mass number
This term is a technical specification used exclusively in nuclear physics and chemistry to identify the isotope of an element. It differs from atomic number, which counts only protons, by including the sum of both protons and neutrons. It is typically written as a superscript to the left of the element's chemical symbol.
Because it refers to a specific count of particles, it is treated as a countable noun in scientific discourse, though it is most frequently used in the singular when discussing the property of a single atom or a specific isotope.
Meanings
Examples
The mass number is the sum of protons and neutrons in the nucleus.
To find the number of neutrons, subtract the atomic number from the mass number.
Wait, does the mass number include electrons too?
Isotopes of the same element have the same atomic number but different mass numbers.
I wonder if this isotope has a higher mass number than the stable one.
The mass number is written as a superscript to the left of the element symbol.
Check the periodic table to verify the mass number for uranium.