Isotopes: Videos & Practice Problems

Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. This difference in neutron count leads to different mass numbers for each isotope. For example, carbon has three isotopes: carbon-12, carbon-13, and carbon-14, with mass numbers of 12, 13, and 14, respectively. Despite having different mass numbers, all isotopes of an element share the same chemical properties because they have the same number of protons and electrons. The varying neutron count, however, can affect the physical properties, such as stability and atomic mass.

The atomic mass of an element is the weighted average mass of all its isotopes, taking into account their relative abundances. It is different from the mass number, which is the total number of protons and neutrons in a specific isotope. For example, the atomic mass of carbon is approximately 12.011, which is close to the mass number of carbon-12, the most abundant isotope. The slight deviation accounts for the presence of other isotopes like carbon-13 and carbon-14. Atomic mass is crucial for calculating the molar mass of compounds and for understanding the element's behavior in chemical reactions.

Radioactive isotopes are used in medicine for both diagnostic and therapeutic purposes. In diagnostics, isotopes like Technetium-99m are used in imaging techniques such as MRI and PET scans to visualize internal organs and detect abnormalities. In therapy, isotopes like Iodine-131 are used to treat conditions such as hyperthyroidism and certain types of cancer by targeting and destroying diseased cells. The predictable decay rates of these isotopes allow for precise control over the dosage and timing of treatments, making them invaluable tools in modern medicine.

A half-life is the time required for half of the radioactive atoms in a sample to decay. This consistent rate of decay allows scientists to use half-lives for radiometric dating, a method for determining the age of fossils and geological samples. By measuring the remaining amount of a radioactive isotope and comparing it to its known half-life, scientists can calculate the time elapsed since the sample formed. For example, carbon-14 dating is used to date organic materials up to about 50,000 years old, providing valuable insights into historical and prehistorical events.

The three isotopes of carbon are carbon-12, carbon-13, and carbon-14. They all have 6 protons but differ in their number of neutrons: carbon-12 has 6 neutrons, carbon-13 has 7 neutrons, and carbon-14 has 8 neutrons. This difference in neutron count results in different mass numbers: 12, 13, and 14, respectively. Carbon-12 is the most abundant isotope, making up about 99% of all carbon atoms. Carbon-13 is stable but less abundant, while carbon-14 is radioactive and used in radiometric dating due to its predictable decay over time.