Actinoids
According to current IUPAC terminology, the actinoid (previously actinide) series encompasses the 15 chemical elements that lie between actinium and lawrencium included on the periodic table, with atomic numbers 89 - 103. The actinoid series derives its name from the first element in the series, actinium, and ultimately from the Greek ακτις (aktis), "ray," reflecting the elements' radioactivity.
The actinoid series (An) is included in some definitions of the rare earth elements. IUPAC is currently recommending the name actinoid rather than actinide, as the suffix "-ide" generally indicates ions (moreover, from Greek, the suffix -ide means "sons of actinium", while -oid means "similar to actinium"). There are alternative arrangements of the periodic table that exclude actinium or lawrencium from appearing together with the other actinoids.
The actinoids display less similarity in their chemical properties than the lanthanoid series (Ln), exhibiting a wider range of oxidation states, which initially led to confusion as to whether actinium, thorium, and uranium should be considered d-block elements. All actinoids are radioactive.
Only thorium and uranium occur naturally in the earth's crust in anything more than trace quantities. Neptunium and plutonium have been known to show up naturally in trace amounts in uranium ores as a result of decay or bombardment. The remaining actinoids were discovered in nuclear fallout, or were synthesized in particle colliders. The latter half of the series possess exceedingly short half-lives.
The actinoids are typically placed below the main body of the periodic table (below the lanthanoid series), in the manner of a footnote. The full-width version of the periodic table shows the position of the actinoids more clearly.
An organometallic compound of an actinoid is known as an organoactinoid.
Elements in the series[edit]
- Ac (89) Actinium
- Th (90) Thorium
- Pa (91) Protactinium
- U (92) Uranium
- Np (93) Neptunium
- Pu (94) Plutonium
- Am (95) Americium
- Cm (96) Curium
- Bk (97) Berkelium
- Cf (98) Californium
- Es (99) Einsteinium
- Fm (100) Fermium
- Md (101) Mendelevium
- No (102) Nobelium
- Lr (103) Lawrencium
