Actinides on the Periodic Table

Actinides on the periodic table.

Core Concepts

In this tutorial you will learn about the actinide family of elements on the periodic table, as well as actinides applications and uses in today’s world.

Topics Covered in Other Articles

What are Actinides?

Although the periodic table is composed of many different elements, each of those elements can be classified into a certain group. The actinides are a group of 15 different elements located at the very bottom row of the periodic table. You may know this group of elements by a few different names: actinide series or actinoids. These elements range from an atomic number of 89 all the way to atomic number 103. Usually the symbol An is used to refer to any of the actinide series of elements.


Each actinide is a radioactive metal that is very important in nuclear chemistry. Actinium, thorium, protactinium, uranium, neptunium, plutonium, americium, curium, berkelium, californium, einsteinium, fermium, mendelevium, nobelium, and lawrencium are the elements that make up this group. The name actinides comes from the greek work “atkis” which means ray. This name is fitting for this group because it reflects the radioactive tendencies of these elements. The actinides are radioactive in nature. They release large amounts of energy on radioactive decay. Only five of the actinides are found in nature: thorium, protactinium, uranium, neptunium, and plutonium.

Actinides Electron Configuration

The electron configurations for the actinides is referenced using the noble gas radon. The general configuration for the group of elements is [Rn] 5f1-14 6d0-1 7s2.

ActiniumAC[Rn] 5f06d17s2
ThoriumTh[Rn] 5f06d27s2
Protactinium Pa[Rn] 5f26d17s2
UraniumU[Rn] 5f3 6d1 7s2
NeptuniumNp[Rn] 5f4 6d1 7s2
PlutoniumPu[Rn] 5f6 6d0 7s2
AmericiumAm[Rn] 5f6d0 7s2
CuriumCm[Rn] 5f7 6d1 7s2
BerkeliumBk[Rn] 5f9 6d7s2
CaliforniumCf[Rn] 5f10 6d7s2
EinsteiniumEs[Rn] 5f11 6d7s2
FermiumFm[Rn] 5f12 6d7s2
MendeleviumMd[Rn] 5f13 6d7s2
NobeliumNo[Rn] 5f14 6d7s2
LawrenciumLr[Rn] 5f14 6d7s2

Ionic Radius and Atomic Radius Trends

Similar to other groups of elements in the periodic table the ionic radius of the actinide series decreases successively along the series. This trend in ionic radius decrease among the actinides is known as actinides contraction. The atomic size and ionic radius decreases smoothly from An to Lr. This is because of the increasing nuclear charge and the electrons that come into the f orbitals of these elements. Due to the bad shielding effect by the 5f electrons the contraction is longer along this period.

Actinides radii.png

Ionization Trends of actinides

The ionization energy of actinides is the energy that is needed to release one electron from the valence shell. The ionization energy of actinides usually differ. The actinides are arranged in terms of increasing atomic number. When the atomic number increases so does the ionization energy. The ionization energies for each element are as follows:

  • Actinium (Ac): 5.17(12)
  • Thorium (Th): 6.08(12)
  • Protactinium (Pa): 5.89(12)
  • Uranium (U): 6.05(7)
  • Neptunium (Np): 6.20(12)
  • Plutonium Pu: 6.06(2)
  • Americium (Am): 5.993(10)
  • Curium (Cm): 6.09(2); 
  • Berkelium (Bk): 6.30(9)
  • Californium (Cf): 6.41(10)
  • Einsteinium (Es): 6.52(10)
  • Fermium (Fm): 6.64(11)
  • Mendelevium (Md): 6.74(12)
  • Nobelium (No): 6.84

Characteristics of the Actinides

Most actinides will share the following properties:

  • Each of these elements are radioactive. This means the element has no stable isotopes.
  • The actinides are highly electropositive. Meaning they often form cations.
  • The actinides that are classified as metals tarnish quickly in the air.
  • Actinides are very dense metals. There are often many allotropes that can be formed, for example plutonium has at least six different allotropes. The only exception to this rule is actinium.
  • This group, when reacted with water or acid, will release hydrogen gas.
  • This family of elements are very malleable and ductile.
  • They are solid at room temperature and are primarily silver colored.
  • The actinides will always fill the 5f subshell. These elements have properties that are similar to d and f block elements.

Actinide Applications

Usually we do not come into much contact with theses elements in our daily lives because they are so radioactive. Elements like Americium can be found in smoke detectors, while thorium can be found in gas fireplace mantles. Actinium is often used in scientific research as am indicator or a gamma source. Most of the actinides we use in the real world get put into energy production, and defense.