Actinide

Encyclopedia : A : AC : ACT : Actinide

Atomic No.	Name	Symbol
89	Actinium	Ac
90	Thorium	Th
91	Protactinium	Pa
92	Uranium	U
93	Neptunium	Np
94	Plutonium	Pu
95	Americium	Am
96	Curium	Cm
97	Berkelium	Bk
98	Californium	Cf
99	Einsteinium	Es
100	Fermium	Fm
101	Mendelevium	Md
102	Nobelium	No
103	Lawrencium	Lr

The actinide series encompasses the 15 chemical elements that lie between actinium and lawrencium on the periodic table with atomic numbers 89 - 103. The actinide series is named after actinium. All actinides are f-block elements except lawrencium. There are also alternative arrangements which do not include either actinium or lawrencium in the actinide series.

The actinides display less similarity in their chemical properties than the lanthanide series, for instance 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 actinides are radioactive.

Only actinium, thorium and uranium occur naturally in the earth's crust. The remaining actinides were synthesized in the 20th century by techniques such as neutron bombardment. The latter half of the series possess exceedingly short half-lives.

The actinides are typically placed below the main body of the periodic table, in the manner of a footnote. The full-width version of the periodic table shows the position of the actinides more clearly.

Note that the International Union of Pure and Applied Chemistry (IUPAC) are currently recommending the name actinoid rather than actinide, as the suffix "-ide" is generally used to indicate anions.

Phase diagram of the actinide elements.