The actinides are a series of 15 chemical elements in the periodic table, ranging from atomic number 89 (actinium) to 103 (lawrencium). These elements are known for their radioactive properties and are typically found in nature in trace amounts. They are all metals and share similar characteristics, such as high density and the ability to form complex compounds. Most actinides are used in nuclear applications, including fuel for nuclear reactors and in the production of nuclear weapons. Some well-known actinides include uranium, which is crucial for nuclear energy, and plutonium, used in both energy generation and military applications.