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Chapter 18: Problem 3

How are the mass and the atomic number of a nucleus affected by the loss of an alpha particle?

Short Answer

Expert verified
The mass number decreases by 4 and the atomic number decreases by 2.

Step by step solution

01

Identify the Components of an Alpha Particle

An alpha particle consists of 2 protons and 2 neutrons. This means it has a mass number of 4 and an atomic number of 2.
02

Determine the Initial Values

Before the emission of an alpha particle, denote the initial mass number of the nucleus as A and the initial atomic number as Z.
03

Calculate the New Mass Number

When a nucleus loses an alpha particle, it loses 2 protons and 2 neutrons, so the mass number decreases by 4. The new mass number is: A' = A - 4.
04

Calculate the New Atomic Number

The nucleus also loses 2 protons, so the atomic number decreases by 2. The new atomic number is: Z' = Z - 2.
05

Summarize the Effects

After the loss of an alpha particle, the new mass number of the nucleus becomes A-4 and the new atomic number becomes Z-2.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

mass number reduction
When a nucleus undergoes alpha particle decay, there is a significant change in its mass number. An alpha particle consists of 2 protons and 2 neutrons. Because the mass number of a nucleus is the total count of its protons and neutrons, losing an alpha particle results in a mass number reduction by 4 units. For instance, if a nucleus had a mass number A, after emitting an alpha particle, the new mass number will be A - 4. This reduction is crucial as it alters the identity and properties of the nucleus.
atomic number reduction
Alongside the reduction in mass number, alpha particle decay also reduces the atomic number of the nucleus. The atomic number is defined as the number of protons in the nucleus. Since an alpha particle contains 2 protons, the loss of an alpha particle decreases the atomic number by 2 units. This change affects the element itself, as the atomic number determines the element's identity in the periodic table. If a nucleus with atomic number Z emits an alpha particle, the new atomic number becomes Z - 2. Thus, the element's symbol and its chemical properties change.
nuclear reactions
Nuclear reactions encompass a broad range of processes where atomic nuclei transform into different nuclei. Alpha decay is one such nuclear reaction, where a nucleus emits an alpha particle (2 protons and 2 neutrons). This emission results in the nucleus changing into a different element's nucleus. By reducing both its mass number (by 4) and its atomic number (by 2), the original nucleus fundamentally alters.
  • **Energy Release:** Alpha decay is often accompanied by the release of energy, indicating that the nucleus moves to a more stable state.
  • **Transmutation:** The process results in the transmutation of elements, where one element transforms into another.
  • **Radioactivity:** Alpha decay is a type of radioactive decay, commonly occurring in heavy elements like uranium and radium.
Understanding nuclear reactions like alpha decay is essential in fields like nuclear physics, radiometric dating, and medical applications.

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