Question

When the isotope bismuth-213 emits an alpha particle, what new element results? What new element results if it instead emits a beta particle?

Short answer

Bismuth-213 becomes thallium-209 with alpha decay.

Step-by-step solution

Understanding Isotopic Decay

When an alpha particle is emitted from an atom, the atom loses 2 protons and 2 neutrons. This decreases both the atomic number and the mass number of the isotope.

Alpha Decay Process

Bismuth-213 has an atomic number of 83. When it emits an alpha particle, its atomic number decreases by 2 (from 83 to 81), and its mass number decreases by 4 (from 213 to 209).

Key concepts

alpha decay

Alpha decay occurs when an unstable atomic nucleus emits an alpha particle to become more stable. An alpha particle consists of two protons and two neutrons, similar to a helium nucleus. This type of decay results in significant changes to the original atom.
For instance, when bismuth-213 undergoes alpha decay, it loses an alpha particle.
This process:

• Reduces the atomic number by 2, because it loses two protons.
• Reduces the mass number by 4, due to the loss of two protons and two neutrons.

After emitting an alpha particle, bismuth-213 - with an atomic number of 83 and a mass number of 213 - will transform into thallium-209 with an atomic number of 81 and a mass number of 209.
This shift results in a new element because the identity of an element is determined by its atomic number.

beta decay

Beta decay transforms a neutron into a proton, or a proton into a neutron, releasing a beta particle in the process. Unlike alpha decay, beta decay does not significantly affect the mass number of the atom as it involves only the transformation of subatomic particles.
In a common type of beta decay, known as beta-minus decay:

• A neutron is converted into a proton.
• An electron (beta particle) is emitted from the nucleus.
• As a result, the atomic number increases by 1, but the mass number remains unchanged.

Thus, if bismuth-213 undergoes beta decay, it retains its mass number of 213 but its atomic number increases from 83 to 84. This changes bismuth-213 into polonium-213. Despite the increase in atomic number, the identity changes due to this gain of a new proton.

atomic number

The atomic number of an element is one of its most specifically defining features. It represents the number of protons in an atom's nucleus, thus uniquely identifying the element.
The atomic number:

• Determines the element's position on the periodic table.
• Defines the type of element and its chemical properties.
• Is crucial in calculating the changes in elemental identity during isotopic decay.

For example, with bismuth-213, which has an atomic number of 83, undergoing isotopic decay processes such as alpha or beta decay, results in changes to the atomic number. These changes lead to the formation of new elements like thallium (when atomic number decreases) or polonium (when atomic number increases).
Understanding the atomic number is key to predicting the outcomes of isotopic decay.

mass number

The mass number of an element is the sum of its protons and neutrons within the nucleus. This number helps provide a complete picture of an isotope’s composition and is essential for understanding isotopic decay.

• Mass number is written as a superscript to the left of the element symbol.
• It helps distinguish between different isotopes of the same element, which have varying numbers of neutrons.
• Mass number typically decreases by 4 during alpha decay, due to the loss of two protons and two neutrons.

For bismuth-213, the mass number is 213, indicating the total number of protons and neutrons. As a result of alpha decay, the mass number decreases to 209. However, in beta decay, the mass number remains constant as only the nuclear particle type changes, not their total number.
Understanding mass number is crucial for determining the effects of different decay processes on atomic composition.