Given the properties described in the question, let's analyze each step carefully to determine which isotope corresponds to an alpha particle.
1. Understanding Alpha Particles:
- Each alpha particle comprises 2 protons and 2 neutrons.
- This makes the total mass number of an alpha particle [tex]\(2 + 2 = 4\)[/tex].
2. Isotopic Notation:
- An isotope is often represented as [tex]\(\text{Element-Symbol (total number of protons + neutrons)}\)[/tex].
3. Evaluating Each Option:
- Lithium-7:
- Lithium (Li) has an atomic number of 3 (3 protons).
- This isotope is [tex]\( \text{Li-7} \)[/tex], meaning it has 7 - 3 = 4 neutrons.
- So it has 3 protons and 4 neutrons, which does not match an alpha particle (2 protons and 2 neutrons).
- Helium-4:
- Helium (He) has an atomic number of 2 (2 protons).
- This isotope is [tex]\( \text{He-4} \)[/tex], meaning it has 4 - 2 = 2 neutrons.
- So it has 2 protons and 2 neutrons, which matches an alpha particle exactly.
- Hydrogen-2:
- Hydrogen (H) has an atomic number of 1 (1 proton).
- This isotope is [tex]\( \text{H-2} \)[/tex], meaning it has 2 - 1 = 1 neutron.
- So it has 1 proton and 1 neutron, which does not match an alpha particle.
- Helium-2:
- Helium (He) has an atomic number of 2 (2 protons).
- This isotope is [tex]\( \text{He-2} \)[/tex], meaning it has 2 - 2 = 0 neutrons.
- So it has 2 protons and 0 neutrons, which does not match an alpha particle.
4. Conclusion:
- Among the given options, the isotope that matches the properties of an alpha particle (2 protons and 2 neutrons) is helium-4.
The correct answer is: helium-4.
So, an alpha particle is also referred to as the nucleus of helium-4.
