Problem 60 - Introductory Chemistry Atoms First

Question

What kind of nucleus would be likely to eject two neutrons and two protons?

Step-by-Step Solution

Answer

A nucleus that would be likely to eject two neutrons and two protons would be a heavy nucleus, specifically one with an atomic number greater than 82. Examples of such nuclei are isotopes of uranium, thorium, radium, and polonium, which undergo alpha decay, releasing an alpha particle consisting of two protons and two neutrons to achieve a more stable configuration.

Step 1: Understand the decay process that ejects two protons and two neutrons

The process of ejecting two protons and two neutrons simultaneously is known as alpha decay. An alpha particle consists of two protons and two neutrons. When a heavy nucleus undergoes alpha decay, it releases an alpha particle which reduces the atomic number by 2 and the mass number by 4, resulting in a more stable daughter nucleus.

Step 2: Identify the elements that undergo alpha decay

Elements with a high atomic number, specifically those with an atomic number greater than 82 (lead), are known to undergo alpha decay. Examples of such elements include uranium, thorium, radium, and polonium.

Step 3: Determine the likely nucleus

Since we are looking for a nucleus that would be likely to eject two neutrons and two protons (an alpha particle) through decay, we can conclude that it must be a heavy nucleus. To be more specific, nuclei or isotopes of elements with atomic numbers greater than 82 are likely candidates for alpha decay. These include isotopes of uranium, thorium, radium, and polonium, among others.

Key Concepts

Nuclear Chemistry

Nuclear chemistry is a field of chemistry that deals with the chemical and physical properties of elements as influenced by changes in the structure of the atomic nucleus. This area of study is key to understanding the processes that power our sun, nuclear reactors, and the principles behind various medical imaging devices.

In nuclear chemistry, we delve into reactions that involve changes in nuclear composition. This includes the phenomenon of radioactive decay, which is the process by which an unstable atomic nucleus loses energy by emitting radiation. An important concept within this field concerns the stability of an atom’s nucleus, which depends on the number of protons and neutrons it contains. When the proportion of neutrons to protons is imbalanced, it can result in a nucleus that is unstable, leading to radioactive decay to achieve stability.

Radioactive Decay

Radioactive decay is a spontaneous process where an unstable atomic nucleus releases energy by emitting particles or electromagnetic waves. There are several types of radioactive decay, including alpha decay, beta decay, and gamma decay.

Alpha decay is particularly relevant when considering nuclei that are likely to eject two protons and two neutrons. In alpha decay, an unstable nucleus emits an alpha particle, which is essentially a helium-4 nucleus, resulting in a decrease in both the atomic number and mass number of the original element. This process tends to occur in elements with larger, heavier nuclei, often making the resulting daughter nucleus more stable by reducing its size and restructuring its components for a more balanced nuclear composition.

Atomic Number

The atomic number, often denoted by the letter Z, is a fundamental property of an element and indicates the number of protons in the nucleus of an atom. This number is critical because it defines the element itself; each element has a unique atomic number. For instance, hydrogen has an atomic number of 1, while carbon has an atomic number of 6.

During alpha decay, the atomic number of the original element decreases by 2. This is because an alpha particle, which consists of 2 protons, is emitted from the nucleus. Since atomic number defines the identity of an element, this decay process transforms the original element into a different element that is two spots earlier on the periodic table.

Isotopes

Isotopes are variants of a particular chemical element which have the same number of protons (and thus the same atomic number) but a different number of neutrons. This results in different mass numbers for the isotopes. Isotopes can be stable or unstable (radioactive).

When discussing alpha decay, isotopes play a central role. Heavier isotopes with imbalanced neutron to proton ratios, especially those of elements with an atomic number greater than 82, are prone to alpha decay. They seek stability through shedding excess particles, such as in the case where a nucleus emits an alpha particle composed of two neutrons and two protons. This results in the creation of an isotope of a different element, with its atomic number reduced by 2 and mass number reduced by 4.