Question

Naturally occurring iodine is iodine-127. The radioactive isotopes of iodine- 125 and iodine- 130 are used in nuclear medicine. a. Write the atomic symbol for each isotope. b. In what ways are the isotopes similar and in what ways do they differ?

Short answer

The atomic symbols are \( I_{53}^{127} \), \( I_{53}^{125} \), and \( I_{53}^{130} \). They are the same element with differing neutrons: iodine-125 (72), iodine-127 (74), and iodine-130 (77).

Step-by-step solution

Understand the Atomic Symbol

The atomic symbol for an element includes its chemical symbol, the atomic number (number of protons), and the mass number (sum of protons and neutrons).

Write the Atomic Symbols

For iodine-127, iodine-125, and iodine-130, the chemical symbol is 'I' and the atomic number is 53. The mass number is the number following the element name: 127, 125, and 130 respectively. Hence, the atomic symbols are \( I_{53}^{127} \), \( I_{53}^{125} \), and \( I_{53}^{130} \).

Compare the Isotopes

To compare the isotopes, note that all three have the same number of protons (53) but different numbers of neutrons. The number of neutrons is calculated as: \[ \text{Number of neutrons} = \text{Mass number} - \text{Atomic number} \]Thus, For iodine-127: 127 - 53 = 74 neutrons. For iodine-125: 125 - 53 = 72 neutrons. For iodine-130: 130 - 53 = 77 neutrons.

Summarize Similarities and Differences

Similarities: All isotopes have 53 protons and belong to the element iodine.Differences: They have different numbers of neutrons and hence different mass numbers. Iodine-125 has 72 neutrons, iodine-127 has 74 neutrons, and iodine-130 has 77.

Key concepts

atomic symbol

The atomic symbol is a shorthand way of representing an element and its specific isotopes. It combines three important pieces of information: the chemical symbol of the element, the atomic number, and the mass number. The chemical symbol for iodine is 'I'.
The atomic number, which is always located as a subscript, tells us the number of protons in the nucleus of an atom. For iodine, this number is 53. Finally, the mass number, which is shown as a superscript, represents the total number of protons and neutrons in the atom's nucleus.
For example, the atomic symbol for iodine-127 is written as: \( I_{53}^{127} \). This compact form allows chemists and students alike to quickly gather essential information about a particular isotope.

mass number

The mass number is a critical part of the atomic symbol and is used to distinguish between different isotopes of an element. While all isotopes of an element have the same number of protons, their mass numbers differ because they have different numbers of neutrons.
For iodine, the mass numbers of the isotopes mentioned are 127, 125, and 130. These numbers are written as superscripts in the atomic symbol and provide the total count of protons and neutrons combined.
To find the number of neutrons in an isotope, you can subtract the atomic number from the mass number: \[ \text{Number of neutrons} = \text{Mass number} - \text{Atomic number} \]. This is why iodine-127 has 74 neutrons, iodine-125 has 72 neutrons, and iodine-130 has 77 neutrons.

neutrons

Neutrons are neutral particles found in the nucleus of an atom, along with protons. They play an essential role in the stability of the nucleus. The number of neutrons varies between different isotopes of the same element, which is why isotopes have different mass numbers.
For iodine isotopes: iodine-127 has 74 neutrons, iodine-125 has 72 neutrons, and iodine-130 has 77 neutrons. Knowing how to calculate the number of neutrons helps in understanding the differences between these isotopes despite their shared chemical properties, as they all have the same element symbol 'I' and atomic number 53.

protons

Protons are positively charged particles located in the nucleus of an atom. The number of protons in an atom is known as the atomic number, which defines the element. For iodine, this number is always 53.
Since all isotopes of iodine must have 53 protons to remain iodine, this remains constant. What makes isotopes unique from one another is the number of neutrons, not protons. Therefore, understanding that all iodine isotopes, such as iodine-125, iodine-127, and iodine-130, have the same 53 protons helps highlight both their similarities and the importance of neutrons in differentiating them.

radioactive isotopes

Radioactive isotopes are variants of elements that have unstable nuclei and emit radiation as they decay to a more stable form. For iodine, isotopes like iodine-125 and iodine-130 are radioactive. These isotopes decay over time, releasing particles and energy in the process.
Radioactive isotopes are incredibly useful in medicine, particularly in diagnostics and treatment. Iodine-125, for example, is used in medical imaging and in treating certain types of cancer. Being familiar with these applications is important for students as it highlights the real-world significance of understanding isotopes. Not all isotopes of iodine are radioactive; iodine-127 is a stable isotope and does not emit radiation.