Actinides: Definition, Properties & Uses

Lesson Transcript
Instructor: Danielle Reid

Danielle has taught middle school science and has a doctorate degree in Environmental Health

There is a family of elements found on the periodic table called actinides. Explore this lesson to learn about what the actinides are, their properties, and uses. Test your knowledge with a short quiz.

Location of the Actinides

Do your eyes ever glaze over when looking at the periodic table? It can look like an impossible jumble of letters and numbers, but it helps if you break them up into sections and learn about what defines them.

Can you spot an actinide on a periodic table? Well if you look at the periodic table on screen now, you will see a dark pink row at the very bottom. A row in a periodic table is called a period. The actinides are located on period 7, the 7th row.

Standard periodic table. The actinides are the bottom row representing a part of Period 7
periodic table

A great way to remember the location of actinides is to pay attention to the first element in this row. The first element has an atomic symbol of Ac, which matches to the first two letters in Actinide. Hence, whenever looking for elements in the actinide family, spotting this symbol will make sure you are looking at the right period. Now you know where to locate the actinides, but what is an actinide?

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  • 0:02 Location of the Actinides
  • 0:56 Definition of Actinide
  • 2:37 Properties of Actinides
  • 3:55 Different Uses of Actinides
  • 4:43 Lesson Summary
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Definition of Actinide

Actinides consist of a family of 15 elements that range in atomic numbers from 89 to 103. Think of the atomic number as a way to identify an element on a periodic table. The 15 elements include: Actinium (Ac), Thorium (Th), Protactinium (Pa), Uranium (U), Neptunium (Np), Plutonium (Pu), Americium (Am), Curium (Cm), Berkelium (Bk), Californium (Cf), Einsteinium (Es), Fermium (Fm), Mendelevium (Md), Nobelium (No), and Lawrencium (Lr).

Until approximately 1940, scientists thought the heaviest atom was uranium, which was the first actinide discovered in the late 1700s. Advancements in science led to the future discoveries of numerous elements we now collectively call actinides. Many of the actinide elements were found or created around 1955 to 1961.

Some actinides are found in nature while others are man-made. Scientists have been able to find five elements from the actinide family in nature: thorium, protactinium, uranium, neptunium, and plutonium. Several actinides were discovered while conducting science experiments; they were artificially made from uranium, called transuranium elements and are mostly short lived.

Properties of Actinides

As mentioned earlier, elements in the actinide family are heavy due to their large atomic mass. Specifically, elements in this family range in atomic mass from 227g/mol to 262g/mol. If we compare that to hydrogen, which has an atomic mass of 1, you can see that actinide elements are quite heavy.

Another property of actinides is their radioactivity. Actinide elements are all radioactive. Radioactivity refers to the nucleus of an atom that breaks down into smaller particles. These smaller particles include alpha particles, beta particles, and gamma particles. An example of the actinide uranium, undergoing radioactive decay, is shown on screen now.

Uranium-238 Radioactive Alpha Decay to Thorium
thorium equation

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