Actinides - Properties, Uses and Availability
The term actinides are derived from the first element of the series which is actinium. The actinide series are referred to with the symbol an. This series consists of a family of 15 elements that range between 89 and 103. The 15 elements that are part of the Actinides series are as follows: 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).
Scientists earlier in the 1940s believed that the heaviest atom is uranium. But due to constant innovation, advancements and discoveries, more and more elements were found and later added in the series. Together all the numerous elements are called Actinides.
There are few actinides that are present in nature, whereas some actinides are man-made. Five elements of Actinide that are naturally formed are plutonium, neptunium, thorium, protactinium, and uranium. Actinides were also formed during scientific experiments and discoveries.
Properties of Actinides
All the elements in the actinide series are heavy because of their large atomic mass. The elements belonging to this series have an atomic mass ranging from 227g/mol to 262g/mol. The atomic mass of hydrogen is 1 therefore; one can have a clear idea of comparatively how heavier these elements are.
One of the most important properties of actinides is that they are radioactive in nature. The elements in this series are highly radioactive. Radioactive refers to the breaking down of the nucleus into smaller particles. The smaller particles are Alpha particles, Beta particles as well as Gamma Particles. The elements in the Actinide series release a large amount of energy on radioactive decay. The elements of Actinides are used as nuclear reactors and in nuclear weapons. There are different uses of Uranium and Thorium. Some of the elements in the actinides series are also used as smoke detectors. Actinides are typical metals and they have properties of D block and F block elements.
There is a general configuration of Actinides which is referred to as
[Rn] 5f1-146d0-7 7s2
In this equation, Rn refers to the nearest noble gas which is Radium.
The f block of the modern periodic table consists of Lanthanides and Actinides.
Similarities Between Lanthanides and Actinides
(n-2)f subshell is used for filling and characterization of all the elements in the Lanthanides and Actinides. The electronic configuration of Lanthanides and Actinides are pretty much similar. Some of the major similarities between these two are listed below:
Lanthanides and Actinides have a prominent Oxidation State that is +3.
(n-2) f orbitals are involved in filling of these elements.
The Lanthanides and Actinides are reactive as well as electropositive.
As the atomic number of these elements increases, the ionic and atomic size decreases.
Both Lanthanides and Actinides have considerable magnetic properties.
Differences Between Lanthanides and Actinides
4f-orbitals are involved in the filling of Lanthanides, whereas the 5f-orbitals are involved in the filling of Actinides. The energy that binds this atom that is 4f is comparatively less than that of actinides which is 5f electrons. The shielding of the 5f electrons is also less when compared to that of 4f electrons. It is very easy to explain the paramagnetic properties of Lanthanides. On the other hand, in the case of Actinides, one cannot easily explain all the paramagnetic properties. Most of the Lanthanides are non-Radioactive except for Promethium. All the elements in the Actinide series are Radioactive in nature. There are several oxocation of the elements in the Actinides series whereas there is no oxocation in Lanthanides. The compounds that are formed by Actinides are very basic in nature as opposed to the compounds found by Lanthanides. The lanthanides and actinides are often called inner transition metals.
Properties of Actinides
The actinides are Metals which are typical in nature. The actinides are soft, shiny, silver in color and have a good density and plasticity. Some of the actinides can also be cut with the help of a simple knife. Thorium has a similar hardness to soft steel and can be heated to roll into sheets or pull into a wire. The properties of elements in the actinide series are the same as the d-block. They can lose to multiple electrons and form a variety of ions. Actinium has a crystalline phase and is not radioactive as well as paramagnetic. The actinides are also pyrophoric, that is they ignite spontaneously when exposed to the air.
The melting point of Actinides does not depend on the number of f electrons. Actinides react very easily because of halogens and chalcogens. Actinides having less number of 5f electrons are used for hybridization. Actinides also have a considerable number of valence States. The actinides also react with the boiling water or with the dilute acid to form the hydrogen gas. The elements of the actinide series are ductile as well as malleable. The actinides can be combined positively with the non-metals.
Availability of Actinide
The two actinide elements are found in abundance in earth's crust; they are Thorium and Uranium. One can also find small quantities of Plutonium, Neptunium in Uranium. Some of the elements in the actinide series are synthetic elements. These elements are called synthetic elements, as they are not formed naturally, they are formed due to the decay of some part of a heavier element. The actinide element tarnishes when exposed to air.
Uses of Actinides
Actinides such as Americium are used in smoke detectors. Thorium is used mainly in Gas mantles. Scientists and researchers use Actinium to carry out scientific research or study. Actinium is used as a gamma source, indicator, and neutron source. A large number of actinides are used for defense operations, nuclear weapons and for the production of energy.
Plutonium is used in nuclear reactors and for nuclear bombs as well. Many of the actinide elements are used in nuclear power plants and also for the production of electronic power. Every actinide is known for its unique atomic number and its different properties as well as characteristics. It is very important to study the chemical and physical properties of actinides to predict its reaction. The actinides do not have stable isotopes.
Conclusion
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FAQs on Actinides
1. What are actinides and where are they located in the periodic table?
Actinides are a series of 15 metallic chemical elements with atomic numbers from 89 (Actinium) to 103 (Lawrencium). They are located in the f-block of the periodic table, typically shown as a separate row below the main body, directly under the lanthanides. This placement helps keep the periodic table's layout manageable.
2. What is the general electronic configuration of actinides?
The general valence shell electronic configuration for actinides is [Rn] 5f1-14 6d0-1 7s2, where [Rn] represents the electron core of the noble gas Radon. The differentiating electrons progressively fill the 5f orbital, which determines the unique properties of the series.
3. What are the main physical and chemical properties of actinides?
Actinides share several characteristic properties, including:
- They are all radioactive metals, with radioactivity increasing with atomic number.
- They are typically silvery-white, dense, and highly electropositive.
- They exhibit variable oxidation states due to the small energy difference between 5f, 6d, and 7s orbitals.
- Many form coloured ions in aqueous solutions.
- They are highly reactive and can tarnish readily in air.
4. Why are all actinide elements radioactive?
Actinides are radioactive because their atomic nuclei are extremely large and unstable. The high number of protons creates significant electrostatic repulsion that the strong nuclear force struggles to overcome. This imbalance leads to spontaneous radioactive decay, where the nucleus emits particles (like alpha or beta) and energy to transform into a more stable, smaller nucleus.
5. How do the properties of actinides differ from those of lanthanides?
While both are f-block elements, actinides differ from lanthanides in several key ways:
- Radioactivity: All actinides are radioactive, whereas most lanthanides (except promethium) are stable.
- Oxidation States: Actinides show a much wider range of oxidation states (e.g., +3 to +7) because their 5f, 6d, and 7s orbitals are very close in energy. Lanthanides predominantly show a +3 oxidation state.
- Complex Formation: Actinides have a greater tendency to form complexes than lanthanides due to the participation of 5f orbitals in bonding.
- Basicity: Actinide compounds are generally more basic than the corresponding lanthanide compounds.
6. What is meant by actinoid contraction and why does it occur?
Actinoid contraction is the steady decrease in atomic and ionic radii across the actinide series with increasing atomic number. This phenomenon occurs because electrons are added to the inner 5f subshell, which provides very poor shielding of the nuclear charge. Consequently, the effective nuclear charge experienced by the outer electrons increases, pulling them closer to the nucleus and causing the radius to shrink.
7. Are all actinides naturally occurring elements?
No, only the first few actinides are found in nature. Thorium (Th) and Uranium (U) exist in significant quantities in the Earth's crust. Traces of Actinium (Ac) and Protactinium (Pa) are also found as decay products in uranium ores. The elements beyond uranium, known as transuranic elements, are synthetic and created artificially in nuclear reactors or particle accelerators.
8. What are some important real-world applications of actinide elements?
Actinides have significant applications, primarily due to their nuclear properties. Key uses include:
- Nuclear Fuel: Uranium-235 and Plutonium-239 are the primary fuels used in nuclear power plants for energy generation and in atomic weapons.
- Smoke Detectors: Americium-241 is commonly used in household smoke detectors as a source of alpha particles for ionization.
- Neutron Sources: Californium-252 is a powerful neutron source used in cancer therapy and to inspect airline luggage for explosives.
- Gas Mantles: Thorium oxide was historically used in gas mantles for its ability to glow brightly when heated.
