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Isotopes of an element have the same number of protons but different numbers of neutrons. For example, carbon-12 and carbon-14 are isotopes of carbon.

Isotopes can be stable or unstable (radioactive). Stable isotopes do not change over time, while radioactive isotopes decay, emitting radiation.

Isotopes are commonly denoted by the element's symbol and mass number.

1. Carbon-14:

   • Carbon-14 is a radioactive isotope used in radiocarbon dating to determine the age of archaeological and geological samples up to about 50,000 years old.

2. Deuterium and Tritium:

   • Hydrogen has two well-known isotopes: deuterium, which has one neutron, and tritium, which has two neutrons. Deuterium is used in heavy water, while tritium is used in nuclear fusion reactions.

3. Uranium-235 and Uranium-238:

   • Uranium-235 is used as fuel in nuclear reactors and nuclear weapons due to its ability to undergo fission. Uranium-238 is more abundant and is used in breeder reactors to produce plutonium-239.

Medical Applications

1. Technetium-99m:

   • Technetium-99m is a widely used radioactive isotope in medical imaging. It helps doctors diagnose conditions by imaging organs and tracking their functions.

2. Iodine-131:

   • Iodine-131 is used in the treatment of thyroid cancer and hyperthyroidism. It selectively targets thyroid tissue, making it effective for medical therapies.

Environmental and Biological Roles

1. Oxygen Isotopes in Climate Studies:

   • Oxygen has three stable isotopes O-16 O-17, and O-18. The ratio of O-18 to O-16 is used to study past climate changes in the ice age.

2. Nitrogen Isotopes in Ecology:

   • The ratio of nitrogen-15 to nitrogen-14 in organisms can provide information about their diet and trophic levels in ecosystems.

Nuclear Power and Energy

1. Plutonium-239:

   • Plutonium-239 is a key isotope used in nuclear reactors and nuclear weapons. It is produced from uranium-238 in breeder reactors.

2. Thorium-232:

   • Thorium-232 is a fertile isotope that can be converted into fissile uranium-233 in thorium reactors, offering a potential alternative to traditional uranium-based nuclear power.