Actinides15 elements · the second of the two rows shown separately below the main table (period 7)

The actinides are the 15 elements from actinium (89) to lawrencium (103), shown in the second separate row beneath the main table. All are radioactive. Only thorium and uranium occur naturally in large amounts; the elements after uranium (the transuranium elements) are made in nuclear reactors or particle accelerators. Uranium and plutonium are the key fuels of nuclear power.

# Properties of actinides

Fill the 5f orbitals
All are radioactive
Thorium and uranium occur naturally in quantity
Elements beyond uranium are synthetic
Used as nuclear fuel and in smoke detectors

# List of actinides

#	Symbol	Element	Atomic mass	Electron configuration	State at 25 °C	Melting point
89	Ac	Actinium	227	[Rn] 6d¹ 7s²	solid	1323 K
90	Th	Thorium	232.04	[Rn] 6d² 7s²	solid	2115 K
91	Pa	Protactinium	231.04	[Rn] 5f² 6d¹ 7s²	solid	1841 K
92	U	Uranium	238.03	[Rn] 5f³ 6d¹ 7s²	solid	1405.3 K
93	Np	Neptunium	[237]	[Rn] 5f⁴ 6d¹ 7s²	solid	917 K
94	Pu	Plutonium	[244]	[Rn] 5f⁶ 7s²	solid	912.5 K
95	Am	Americium	[243]	[Rn] 5f⁷ 7s²	solid	1449 K
96	Cm	Curium	[247]	[Rn] 5f⁷ 6d¹ 7s²	solid	1613 K
97	Bk	Berkelium	[247]	[Rn] 5f⁹ 7s²	solid	1259 K
98	Cf	Californium	[251]	[Rn] 5f¹⁰ 7s²	solid	1173 K
99	Es	Einsteinium	[252]	[Rn] 5f¹¹ 7s²	solid	1133 K
100	Fm	Fermium	[257]	[Rn] 5f¹² 7s²	predicted solid	1800 K
101	Md	Mendelevium	[258]	[Rn] 5f¹³ 7s²	predicted solid	1100 K
102	No	Nobelium	[259]	[Rn] 5f¹⁴ 7s²	predicted solid	1100 K
103	Lr	Lawrencium	[266]	[Rn] 5f¹⁴ 7s² 7p¹	predicted solid	1900 K

# Actinides FAQ

Which elements are actinides?

There are 15 actinides in this table: Actinium, Thorium, Protactinium, Uranium, Neptunium, Plutonium, Americium, Curium, Berkelium, Californium, Einsteinium, Fermium, Mendelevium, Nobelium, Lawrencium.

Where are the actinides on the periodic table?

The actinides are found in the second of the two rows shown separately below the main table (period 7).

What are the properties of actinides?

Fill the 5f orbitals; All are radioactive; Thorium and uranium occur naturally in quantity; Elements beyond uranium are synthetic; Used as nuclear fuel and in smoke detectors.

# Other element categories

●Alkali metals ●Alkaline earth metals ●Transition metals ●Post-transition metals ●Metalloids ●Reactive nonmetals ●Halogens ●Noble gases ●Lanthanides