Actinides of the Periodic Table

The actinides are the 15 elements from actinium to lawrencium, part of the f-block, and all of them are radioactive. There are 15 elements of this category in the periodic table, from Actinium (Ac), atomic number 89, to Lawrencium (Lr), atomic number 103.

Actinides at a glance

Number of elements: 15
Phase under standard conditions: Solid 15 elements

Element list

Atomic no.	Symbol	Name	Atomic mass	Phase	Short configuration
89	Ac	Actinium	227	Solid	[Rn] 6d¹ 7s²
90	Th	Thorium	232.04	Solid	[Rn] 6d² 7s²
91	Pa	Protactinium	231.04	Solid	[Rn] 5f² 6d¹ 7s²
92	U	Uranium	238.03	Solid	[Rn] 5f³ 6d¹ 7s²
93	Np	Neptunium	237	Solid	[Rn] 5f⁴ 6d¹ 7s²
94	Pu	Plutonium	244	Solid	[Rn] 5f⁶ 7s²
95	Am	Americium	243	Solid	[Rn] 5f⁷ 7s²
96	Cm	Curium	247	Solid	[Rn] 5f⁷ 6d¹ 7s²
97	Bk	Berkelium	247	Solid	[Rn] 5f⁹ 7s²
98	Cf	Californium	251	Solid	[Rn] 5f¹⁰ 7s²
99	Es	Einsteinium	252	Solid	[Rn] 5f¹¹ 7s²
100	Fm	Fermium	257	Solid	[Rn] 5f¹² 7s²
101	Md	Mendelevium	258	Solid	[Rn] 5f¹³ 7s²
102	No	Nobelium	259	Solid	[Rn] 5f¹⁴ 7s²
103	Lr	Lawrencium	262	Solid	[Rn] 5f¹⁴ 7s² 7p¹

Frequently asked questions

Which elements are the actinides?

The actinides are Actinium, Thorium, Protactinium, Uranium, Neptunium, Plutonium, Americium, Curium, Berkelium, Californium, Einsteinium, Fermium, Mendelevium, Nobelium and Lawrencium.

How many elements are in the actinides category?

The periodic table has 15 elements in the actinides category.