| Atomic Number | Mass Number |
|---|---|---|
Represents | The total number of protons present in the nucleus of an atom. | Total count of protons and neutrons present in the nucleus of an atom. |
Symbol | Z (AZE) Found at the subscript of the AZE notation while representing the element (E). | A (AZE) Written in the superscript of the AZE notation while representing the element (E). |
Significance | - Uniquely identifies an element. The periodic table is built in the increasing order of atomic numbers of all known elements. - The proton number is always equal to the number of electrons outside an atom's nucleus (extra-nuclear). | Adds to the mass of an atom. Since the mass is concentrated in the nucleus of an atom, it accounts for the 99.9% of mass of an atom. |
Type of Number | Always a whole number. | Always a whole number. |
Variation | The proton number for an element is always fixed. Any variation in the count of protons signifies another element. | An element capable of existing as an isotope can have different mass numbers. So, an isotope can have the same number of protons but a different number of neutrons, so the mass number of each isotope of an element can be different. |
Difference | The atomic number is distinct from atomic weight, atomic mass, and isotopes. | The mass number is different from the standard atomic weight of an element that considers the average of all the isotopes of an element. In comparison, the mass number counts the protons and neutrons of each element separately. |
Reaction | In nuclear reactions, the atomic number changes. In chemical reactions, the atomic number remains unaffected. | In nuclear reactions, the mass number changes. A significant imbalance between the number of protons and neutrons can cause nuclear instability and disintegration. In chemical reactions, the mass number remains unaffected. |
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