In nuclear chemistry, alpha (α) particles emitted from radioactive nuclei are best described as which of the following?

Introduction / Context:
This question is about the nature of alpha particles in radioactivity. Alpha decay is a common type of nuclear decay, especially for heavy nuclei such as uranium and radium. Knowing what an alpha particle actually is helps in understanding its charge, mass, penetrating power and biological effects.

Given Data / Assumptions:

• We are dealing with alpha particles emitted during radioactive decay.
• Options include electrons, hydrogen ions, X ray radiation, helium nuclei and gamma photons.
• We assume basic nuclear physics knowledge about types of radiation: alpha, beta and gamma.
• We consider the standard definition used in textbooks and examinations.

Concept / Approach:
An alpha particle is essentially the nucleus of a helium atom. It contains two protons and two neutrons, giving it a mass number of 4 and a positive charge of +2 (because of two protons and no electrons). When a heavy nucleus emits an alpha particle, its atomic number decreases by 2 and its mass number decreases by 4. Because alpha particles are relatively heavy and positively charged, they have low penetrating power but high ionising power. They are very different from electrons, X rays or gamma rays.

Step-by-Step Solution:
1) Recall that alpha decay involves emission of an alpha particle from the nucleus of a heavy atom.2) Experimental evidence, such as deflection in electric and magnetic fields and measurement of mass and charge, shows that alpha particles carry a charge of +2 and have mass about four times that of a proton.3) This combination of charge and mass matches the helium nucleus, which has two protons and two neutrons.4) Therefore, an alpha particle is equivalent to a helium nucleus (He2+), often written as 4He2+ or simply α.5) High energy electrons correspond to beta minus particles, not alpha particles.6) X rays and gamma rays are forms of electromagnetic radiation with no rest mass and no charge, so they cannot be alpha particles.7) Thus, the correct description of an alpha particle is a double positively charged helium nucleus.

Verification / Alternative check:
When alpha particles are slowed and captured by matter, they often pick up two electrons and become neutral helium atoms, which can be detected in sealed radioactive sources over time. This observation further supports that alpha particles are helium nuclei. Rutherford scattering experiments used alpha particles and their known mass and charge to draw conclusions about atomic structure. These historical and experimental facts confirm that alpha particles are not electrons, hydrogen ions or photons, but rather helium nuclei with a +2 charge.

Why Other Options Are Wrong:
High energy electrons: These correspond to beta minus particles (β−), not alpha particles.
Positively charged hydrogen ions (protons): A proton is a hydrogen nucleus and has charge +1 and mass 1, while an alpha particle has charge +2 and mass 4.
High energy X ray radiations: X rays are photons of electromagnetic radiation without rest mass or charge.
Neutral gamma ray photons: Gamma rays are also photons, massless and uncharged, and are distinct from particle radiation like alpha emissions.

Common Pitfalls:
Students sometimes mix up different types of radiation because all are emitted from radioactive substances. A good way to remember is: alpha equals helium nucleus, beta equals high speed electron or positron, and gamma equals high energy photon. Remembering that alpha particles are relatively heavy and doubly charged helps explain why they can be stopped by a sheet of paper while beta and gamma rays are more penetrating. This mental picture helps in quickly selecting the correct description in multiple choice questions.

Final Answer:
Alpha particles are double positively charged helium nuclei emitted from the nucleus during alpha decay.