Doubly-charged helium ions
Explanation
Ernest Rutherford’s alpha-particle scattering experiment was instrumental in the discovery of the atomic nucleus. The experiment involved bombarding a thin gold foil with high-energy alpha particles emitted from a radioactive source.
Analysis:
- Alpha particles ($\alpha$-particles) are positively charged particles.
- They are identical to the nucleus of a helium atom. A neutral helium atom consists of two protons, two neutrons, and two electrons.
- When the two electrons are removed from a helium atom, the remaining species consists only of two protons and two neutrons.
- Consequently, it carries a charge of +2 units and a mass of 4 atomic mass units.
- Therefore, alpha particles are doubly-charged helium ions ($He^{2+}$).
- Singly-charged hydrogen ions describes a proton ($H^+$).
- High-energy electrons describes beta particles ($\beta$-particles), which are high-energy electrons.
Key Takeaway:
An alpha particle is a helium nucleus consisting of two protons and two neutrons, represented as $He^{2+}$.