The Actinides, a section of Period 7 of the periodic table with properties similar to the Group 4 element Actinium, comprise:

• #89 – Actinium (Ac), from Greek for beam or ray, actinos
• #90 – Thorium (Th), after Thor, Norse god of thunder
• #91 – Protactium (Pa), from proto-actinium, or “nuclear precursor of actinium”
• #92 – Uranium (U), after the planet Uranus, which was discovered just prior to the element
• #93 – Neptunian (Np), after the planet Neptune
• #94 – Plutonium (Pu), after the (then) planet Pluto
• #95 – Americium (Am), after the Americas, as it lies directly below Europium
• #96 – Curium (Cm), after pioneer radiologists Pierre and Marie Curie
• #97 – Berkelium (Bk), after the town of Berkeley, California, where it was first synthesised
• #98 – Californium (Cf), same as Berkelium
• #99 – Einsteinium (Es), after physicist Albert Einstein
• #100 – Fermium (Fm), after pioneer nuclear physicist Enrico Fermi
• #101 – Mendelevium (Md), after Dmitri Mendeleeve, father of the periodic table
• #102 – Nobelium (No), after chemist Alfred Nobel
• #103 – Lawrencium (Lr), after Ernest Lawrence, inventor of the cyclotron

All of the actinides are radioactive. Of them, only Americium, Neptunian, and Uranium are remotely obtainable. Neptunian and Americium can both be found in household smoke detectors, while Uranium oxide ores can be purchased at flea markets that have a mineral rock booth.