M
Mass Number
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What is Mass Number?
The mass number (A) of a nuclide is the total number of protons and neutrons (nucleons) in its nucleus. It is used together with the atomic number (Z) to specify a particular isotope: ᴬZX. For example, carbon-12 (¹²₆C) has mass number 12 (6 protons + 6 neutrons). The mass number is approximately equal to the atomic mass in atomic mass units.
Key Facts
Term
Mass Number
Index
All "M" terms
Frequently Asked Questions
The mass number (A) of a nuclide is the total number of protons and neutrons (nucleons) in its nucleus. It is used together with the atomic number (Z) to specify a particular isotope: ᴬZX. For example, carbon-12 (¹²₆C) has mass number 12 (6 protons + 6 neutrons). The mass number is approximately equal to the atomic mass in atomic mass units.
More "M" Terms
Macromolecule
Magnesium
Mg
Magnetic Quantum Number
m_l quantum number: −l to +l integers; e.g., p: m_l = −1, 0, +1
Main Group Elements
Manganese
Mn
Manometer
P = ρgh (hydrostatic); manometer measures pressure differential
Mass
Mass Action Expression
Mass Defect
Δm = Z·mₚ + N·mₙ − m_nucleus
Mass Deficiency
Mass Number
A = Z + N
Mass Spectrometer
View all "M" terms →