Rutherford's Alpha Scattering Experiment
- Most $\alpha$-particles passed straight through $\rightarrow$ Most space in an atom is empty.
- Few particles deflected by small angles $\rightarrow$ Positive charge concentrated in small volume.
- $1$ in $12,000$ rebounded back $180^\circ \rightarrow$ Entire mass and positive charge concentrated in a tiny dense core called the Nucleus.
Isotopes vs Isobars:
- Isotopes: Same atomic number $Z$, different mass number $A$ ($^{12}_6C, ^{14}_6C$).
- Isobars: Same mass number $A$, different atomic number $Z$ ($^{40}_{20}Ca, ^{40}_{18}Ar$).
