The actinides are a group of 15 elements found on the bottom row of the periodic table. The group is also known as the actinide series or the actinoids (the term preferred by the IUPAC). The elements run from atomic number 89 to atomic number 103. All are radioactive metals that are important in nuclear chemistry.
Here is a list of the actinides, a look at their properties, their uses, and other interesting facts.
Location on the Periodic Table
On a typical periodic table, the actinides are the bottom row of the table. In this type of periodic table, there are two rows of elements below the main body of the table. The lanthanides (lanthanide series or lanthanoids) are the top row, while the actinides are the bottom row.
On an extended periodic table, the actinides are again on the bottom row. However, they are inserted between radium (atomic number 88) and rutherfordium (atomic number 104). The extended periodic table isn’t as compact, so it isn’t seen as often, but it shows that the actinides are closely related to the transition metals. In fact, the lanthanides and actinides may be called the inner transition metals.
List of Actinides
While there is some dispute over exactly which elements are actinides, most scientists recognize 15 elements in the group. All of these elements are f-block elements (electron configuration includes the f sublevel), except for lawrencium, which is a d-block element. Usually, the actinides run from actinium to lawrencium, although some chemists start the group with thorium. The list of actinides is:
- Actinium (Ac) – atomic number 89
- Thorium (Th)- atomic number 90
- Protactinium (Pa)- atomic number 91
- Uranium (U)- atomic number 92
- Neptunium (Np)- atomic number 93
- Plutonium (Pu)- atomic number 94
- Americium (Am)- atomic number 95
- Curium (Cm)- atomic number 96
- Berkelium (Bk)- atomic number 97
- Californium (Cf)- atomic number 98
- Einsteinium (Es)- atomic number 99
- Fermium (Fm)- atomic number 100
- Mendelevium (Md)- atomic number 101
- Nobelium (No)- atomic number 102
- Lawrencium (Lr)- atomic number 103
The actinides share common properties:
- All actinides elements are radioactive. They have no stable isotopes.
- The actinides successively fill the 5f electron sublevel. Many of these elements share properties with both d-block and f-block elements.
- They are silver-colored metals that are solid at room temperature and pressure.
- The actinides are highly electropositive. They typically have several oxidation states.
- Actinides readily form compounds with most nonmetals.
- The metals readily tarnish in air.
- All of the actinides are relatively soft for metals. Some may be cut with a knife.
- They are malleable and ductile.
- The metals are heavy or dense.
- All of the actinides are pyrophoric. When finely powdered, they spontaneously ignite in air.
- All of the actinides are paramagnetic.
- They have numerous crystal phases or allotropes. Plutonium has at least six allotropes.
- They react with dilute acid or boiling water to produce hydrogen gas.
- The actinides readily undergo nuclear reactions. These reactions release tremendous amounts of energy. Under certain conditions, chain reactions may occur.
Because of their radioactivity, the actinides aren’t encountered much in daily life. The exception is americium, which is found in smoke detectors. Uranium is a nuclear fuel and is used in armor-penetrating ammunition. Actinium is used as a neutron and gamma source and in medical research. Thorium is used in gas mantles. Some actinides find use as colorants in ceramics and glass. For example, uranium gives vaseline glass its yellow-green fluorescence.
Interesting Actinide Facts
- The name for actinium and the actinides comes from the Greek word “aktis” which means ray or beam. The name reflects the radioactive nature of the elements.
- The chemical symbol An may be used to refer to any actinide.
- Five actinides are found in nature: thorium, protactinium, uranium, neptunium, and plutonium. The other actinides are artificial elements that are synthesized in particle accelerators, nuclear reactors, and nuclear explosions. Thorium and uranium are the most abundant actinides, found at concentrations in the Earth’s crust of 16 ppm and 4 ppm, respectively.
- Thorium and uranium were the first actinides to be discovered.
- The fissionable elements are actinides.
- Nuclear weapons tests released at least six actinides heavier than plutonium, including americium, curium, berkelium, californium, einsteinium, and fermium.
- Enrico Fermi predicted the existence of the actinides in 1934. At the time, four actinides were known, but that they formed a group or family similar to the lanthanides was not understood.
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