Problem 32 - A Complete Resource Book in Chemistry for JEE Main

Question

In a radioactive decay, an emitted electron comes from (a) the nucleus of atom (b) the orbit with principal quantum number 1 (c) the inner orbital of the atom (d) the outermost orbit of the atom

Step-by-Step Solution

Answer

The electron comes from the nucleus of the atom, as explained by beta decay.

Step 1: Understanding Radioactive Decay

Radioactive decay is a process where an unstable atomic nucleus loses energy by radiation. Electrons as particles are not emitted from the nucleus during traditional radioactive decays like alpha or beta decay. In beta decay, specifically, a neutron in the nucleus is transformed into a proton, and this process emits an electron, which is called a beta particle.

Step 2: Identify the Source of an Emitted Electron

During beta decay, the emitted electron, known as a beta particle, originates from the transformation of a neutron within the nucleus, not from any electron shells or orbitals around the nucleus. Therefore, the electron does not come from any orbital of the atom itself.

Step 3: Evaluate the Answer Options

Given the four choices, we identify: (a) the nucleus of atom (b) the orbit with principal quantum number 1 (c) the inner orbital of the atom (d) the outermost orbit of the atom Based on our understanding from Steps 1 and 2, the correct answer is that the electron comes from the transformation process occurring in the nucleus.

Key Concepts

Beta Decay

Beta decay is a fascinating process that occurs when an atomic nucleus is unstable. This instability occurs due to an imbalance between protons and neutrons. During beta decay, a neutron transforms into a proton. This transformation also results in the release of a specific electron, referred to as a beta particle. Beta decay can be of two types:

• Beta-minus decay: Here, a neutron within the nucleus becomes a proton, releasing a beta particle (electron) and an antineutrino.
• Beta-plus decay: In this case, a proton transforms into a neutron, leading to the emission of a positron and a neutrino.

This process helps the atom move toward a more stable state. It’s important to note that unlike electrons in outer shells, these particles come from within the nucleus.
This decay process does not involve the traditional electron shells or orbitals. Instead, it is about the intrinsic changes happening at the core of the atom.

Nucleus

The nucleus is the heart of an atom. It is densely packed with protons and neutrons and holds most of the atom's mass. The forces within the nucleus keep these particles tightly bound:

• Protons: These positively charged particles determine the element's identity.
• Neutrons: Neutrally charged, they stabilize the nucleus by reducing repulsive forces between protons.

In radioactive decay, it's essential to understand that changes happen at this level. When beta decay occurs, neutrons and protons can interconvert:

• A neutron can become a proton, releasing a beta particle (electron).
• Conversely, a proton can convert into a neutron, emitting a beta-positive particle (positron).

This precision process at a nuclear level is what governs the stability of the atom, contributing significantly to understanding nuclear chemistry.

Beta Particle

A beta particle is essentially an electron or positron that is emitted during beta decay from the nucleus. Despite being a type of electron, its origin is unique compared to typical electrons found in atomic orbitals.
There are two forms, as mentioned earlier:

• Beta-minus particle: An electron produced when a neutron turns into a proton.
• Beta-plus particle: A positron that forms as a proton converts into a neutron.

These particles are incredibly small and travel at high speeds. They are crucial in the decay process, helping the unstable nucleus reach a more balanced state. Given their emergence from the nucleus, beta particles carry vital information about nuclear reactions and transformations, revealing much about atomic structures and their behaviors.