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Answer to: what is the mass number for chromium-53
The mass number for chromium-53 is 53. In isotope naming, “chromium-53” already states the mass number: it is the total count of nucleons (protons + neutrons) in the nucleus.
Definition
The mass number \(A\) is the total number of nucleons: \[ A = Z + N \] where \(Z\) is the atomic number (protons) and \(N\) is the neutron number (neutrons).
Step-by-step interpretation for chromium-53
- Identify the isotope label: “chromium-53” means \(A = 53\).
- Use the element identity: chromium has atomic number \(Z = 24\) (24 protons).
- Compute the neutron number: \[ N = A - Z = 53 - 24 = 29 \] so the chromium-53 nucleus contains 29 neutrons.
Nuclide symbol (isotope notation)
The nuclide symbol places the mass number as a left superscript and the atomic number as a left subscript:
\[ {}^{53}_{24}\mathrm{Cr} \]The mass number \(A=53\) indicates nucleons, not the average atomic mass found on the periodic table.
Common quantities compared
| Quantity | Symbol | Meaning for chromium-53 |
|---|---|---|
| Atomic number | \(Z\) | 24 protons (defines chromium) |
| Mass number | \(A\) | 53 nucleons total (given by “chromium-53”) |
| Neutron number | \(N\) | \(53 - 24 = 29\) neutrons |
| Average atomic mass | — | A weighted average over naturally occurring isotopes (not equal to \(A\) in general) |
Visualization: reading isotope notation for chromium-53
Final result
The mass number for chromium-53 is 53; the isotope has 24 protons and 29 neutrons.
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