α particles are doubly charged ions of ________.
helium
α particles are a type of radioactive decay product. Understanding their composition is key to answering this question about what element they originate from in terms of their ionic state.
Understanding Alpha Particles and Doubly Charged Ions
An α particle is essentially the nucleus of a helium atom. A neutral helium atom contains 2 protons, 2 neutrons, and 2 electrons. The nucleus of a helium atom contains only the 2 protons and 2 neutrons.
When an atom undergoes alpha decay, it emits an α particle. This particle is a helium nucleus.
The term "doubly charged ions" refers to the charge of the α particle. Since the α particle is a nucleus containing 2 protons (each with a +1 charge) and no electrons (which would have a -1 charge), its net charge is $+2$. This means it has lost its two electrons, making it a doubly charged positive ion.
Therefore, α particles are equivalent to doubly charged helium ions (specifically, the helium nucleus He2+).
Analyzing the Options
Let's look at why the other options are incorrect:
- Lithium: A lithium atom has 3 protons. Its nucleus would be different from a helium nucleus.
- Beryllium: A beryllium atom has 4 protons. Its nucleus is also different from a helium nucleus.
- Hydrogen: A hydrogen atom has 1 proton. Its most common isotope's nucleus is just a single proton. Deuterium has 1 proton and 1 neutron, and Tritium has 1 proton and 2 neutrons. None of these match the composition of an α particle.
Only the nucleus of a helium atom matches the description of an α particle with 2 protons and 2 neutrons, resulting in a $+2$ charge when it is an ion (having lost its electrons).
Composition Comparison
| Particle/Nucleus | Protons | Neutrons | Electrons (in neutral atom) | Net Charge (as nucleus/doubly charged ion) | Matches α particle? |
|---|---|---|---|---|---|
| Hydrogen Nucleus (Protium) | 1 | 0 | 1 | $+1$ | No |
| Lithium Nucleus | 3 | Varies | 3 | $+3$ | No |
| Beryllium Nucleus | 4 | Varies | 4 | $+4$ | No |
| Helium Nucleus | 2 | 2 | 2 | $+2$ | Yes |
The table clearly shows that only the helium nucleus has the composition (2 protons, 2 neutrons) that corresponds to an α particle, and when considered as a doubly charged ion (lacking electrons), it carries a $+2$ charge.
Revision Table: Alpha Particles and Radioactive Decay
| Term | Definition | Key Property |
|---|---|---|
| α Particle | Nucleus of a Helium atom ($^{4}_{2}$He) | Consists of 2 protons and 2 neutrons; has a charge of $+2e$ |
| Doubly Charged Ion | An atom or molecule that has lost two electrons, resulting in a net charge of $+2$ | Example: He$^{2+}$ ion |
| Alpha Decay | A type of radioactive decay where an atomic nucleus emits an α particle | Decreases the atomic number by 2 and the mass number by 4 |
Additional Information: Types of Radioactive Emissions
Besides alpha particles, the two other common types of radioactive emissions are beta particles and gamma rays.
- Beta ($\beta$) Particles: These are high-energy electrons or positrons emitted from the nucleus during beta decay. They have a charge of $-1e$ (electron) or $+1e$ (positron).
- Gamma ($\gamma$) Rays: These are high-energy photons (electromagnetic radiation) emitted from an atomic nucleus. They have no charge and no mass.
α particles are the most massive and least penetrating type of common radioactive emission, while gamma rays are the most penetrating.
Important Questions from Structure of Atom
Identify the element having zero valency
Which non-metal among the following is poly-atomic?
_______ is the most electropositive and ______ is the most electronegative element of the third period of the modern periodic table.
A. Sodium, Potassium
B. Magnesium, Aluminium
C. Sodium, Chlorine
D. Aluminium, Chlorine
_______________ is a discrete packet of energy related to electromagnetic radiation (light), in which energy is E which is proportional to frequency of radiation ν.
The elements belonging to the same group of periodic table have the same-
