Classify a nucleus on the basis of atomic number and mass number, and define them.

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> [!TLDR]
> By $Z$ and $A$: isotopes (same $Z$), isobars (same $A$), isotones (same $N$); $Z$ = protons, $A$ = protons + neutrons.
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> A nucleus is specified by its **atomic number** $Z$ and **mass number** $A$, written ${}_{Z}^{A}X$.
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> **Classification of nuclei:**
> 1. **Isotopes** — nuclei with the **same atomic number $Z$** but different mass number $A$ (same element, different neutrons). Example: ${}_{1}^{1}H,\ {}_{1}^{2}H,\ {}_{1}^{3}H$.
> 2. **Isobars** — nuclei with the **same mass number $A$** but different atomic number $Z$. Example: ${}_{6}^{14}C$ and ${}_{7}^{14}N$.
> 3. **Isotones** — nuclei with the **same number of neutrons** $N=A-Z$ but different $Z$ and $A$. Example: ${}_{6}^{14}C$ and ${}_{8}^{16}O$ (both $N=8$).
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> **Definitions:** …

Feature	Isotopes	Isobars
Atomic number $Z$	same	different
Mass number $A$	different	same
Number of neutrons	different	different
Chemical element	same element	different elements
Example	$^{1}_{1}H,\ ^{2}_{1}H,\ ^{3}_{1}H$	$^{40}_{18}Ar,\ ^{40}_{20}Ca$
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Q.Classify a nucleus on the basis of atomic number and mass number, and define them.

Concept understanding — Composition and Size of the Nucleus

Q.Classify a nucleus on the basis of atomic number and mass number, and define them.

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