Question

When \({ }_{88}^{226} \mathrm{Ra}\) decays by emitting an alpha particle, what is the atomic number of the resulting nucleus? What is the resulting atomic mass?

Short answer

The atomic number is 86, and the atomic mass is 222.

Step-by-step solution

Understanding Alpha Decay

In alpha decay, an atomic nucleus emits an alpha particle, which consists of 2 protons and 2 neutrons. This particle is represented by \({ }_{2}^{4} \text{He}\). As a result, the atomic number decreases by 2, and the atomic mass decreases by 4.

Calculate the New Atomic Number

Start with the original atomic number of radium, which is 88. Subtract 2 from this number to find the atomic number of the resulting nucleus: \[ 88 - 2 = 86 \] Thus, the new atomic number is 86.

Calculate the New Atomic Mass

Begin with the original atomic mass of radium, which is 226. Subtract 4 from this mass to determine the atomic mass of the resulting nucleus: \[ 226 - 4 = 222 \] So, the new atomic mass is 222.

Key concepts

Atomic Number

Every atom has a unique identity, mainly defined by its atomic number. This number is crucial because it tells us how many protons are inside the nucleus of an atom. Protons are positively charged particles, and having a particular number of protons determines what element an atom is. Simply put, the atomic number is what differentiates hydrogen (with 1 proton) from helium (with 2 protons), and so on with the rest of the elements.

For example, radium has an atomic number of 88, meaning there are 88 protons in its nucleus. When radium undergoes alpha decay, it loses an alpha particle, which contains 2 protons, thus decreasing its atomic number by 2. This results in the new element having an atomic number of 86. By interpreting these changes, we learn about elemental transformations in radioactive processes like alpha decay. Such transformations underline why understanding atomic numbers is fundamental in nuclear chemistry.

Atomic Mass

Atomic mass is another essential feature you need to know about atoms. Unlike the atomic number, the atomic mass considers both the protons and the neutrons in the nucleus. Neutrons are neutral particles, and they, along with protons, contribute to the atom's mass.

An atom's mass can affect how it behaves in chemical reactions and also determines how heavy or light the atom is. In an alpha decay process, the atomic mass decreases because the atom is losing 2 protons and 2 neutrons with each alpha particle emitted. This is why the original atomic mass of 226 in radium becomes 222 for the resulting nucleus after alpha decay.

By understanding changes in atomic mass, we begin to see how matter changes and interacts at the nuclear level, providing insights into the stability of the elements.

Nuclear Reactions

Nuclear reactions are fascinating events that occur within an atom's nucleus. Unlike regular chemical reactions that involve electrons and occur outside the nucleus, nuclear reactions involve the protons and neutrons. These reactions can significantly transform elements and alter their basic properties.

There are several types of nuclear reactions, and alpha decay is just one of them. In alpha decay, the nucleus emits an alpha particle, resulting in a change in both the atomic number and atomic mass of the original atom. The changes brought about by such reactions can lead to the formation of entirely different elements.

Understanding nuclear reactions like alpha decay is crucial for many fields, including nuclear energy and medical applications. They demonstrate how elements can transform under specific circumstances and help in the creation of new elements, expanding our understanding of the atomic world.