Danielle has taught middle school science and has a doctorate degree in Environmental Health
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.
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?
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.
In this example we are looking at one isotope of uranium called uranium-238. An isotope is a form of an element where the number of neutrons in the nucleus differs but the protons are the same, making the atomic mass change while the chemical properties remain.
Uranium, along with other actinides, have different isotopes. When the atomic nucleus in uranium undergoes alpha decay, a type of radioactive decay, the end result is the formation of a new element called thorium. The key point to remember with actinides is their ability to undergo the radioactive decay process, thereby producing different chemical elements.
Different Uses of Actinides
In general, actinides are used for a wide variety of purposes. For example, plutonium is used during the manufacturing of nuclear weapons on a large scale (i.e. in larger amounts). On a much smaller scale plutonium is used to power sources through nuclear energy. Another actinide, californium is used to make our smoke detectors while americium is found in our metal detectors and even used for cancer treatment. Going back to uranium, this actinide is used as a rich fuel source at nuclear power plants by converting it to plutonium.
A unique set of elements, the actinide family plays an important part in the production of items that range from everyday uses to specific medicinal purposes. This seemingly obscure set of elements buried in the periodic table is used in our everyday lives!
Actinides represent a family of 15 elements on the periodic table in period 7. The atomic number of these elements range from 89 to 103 while the atomic masses range from 227 to 262g/mol. These elements are all known to be radioactive, which means that the nuclei of their atoms break down into smaller particles. These smaller particles include alpha particles, beta particles, and gamma particles and help form isotopes, which are a form of an element where the number of neutrons in the nucleus differs but the protons are the same, making the atomic mass change while the chemical properties remain. Some elements in the actinide family are naturally found while others are artificially made in the laboratory. Common uses of actinide elements include the production of nuclear weapons, as power sources in the form of nuclear energy, and for medicinal purposes.
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