What are Actinides?

The group of radioactive metallic elements found on the last side of the periodic table is called actinides. These elements range between atomic numbers 89 and 103 on the periodic table.

Apart from Uranium and Thorium, the actinides are mostly composed of man-made elements. These elements play a crucial part in chemistry (nuclear), owing to the characteristics they possess.

The periodic table (Modern) comprises two rows. The lanthanide and actinide elements are found in the first and second rows, respectively. The rationale for the placement of actinides on the second row is attributed to their inability to mix well with the design, so general placement makes the table difficult to comprehend.

Despite that, these two rows of metals are viewed as part of the transition metal group, which is why they are also referred to as the inner transition metals per their natural position on the table and their properties.

The total number of actinides is 15.

Except for Lawrencium, a d-block element, the actinides’ electronic configurations are based on the f-sublevel. As per our understanding of the elements and periodic nature, the arrangements of the elements should be as follows:

1. Actinium-Ac
2. Thorium-Th
3. Protactinium-Pa
4. Uranium-U
5. Neptunium-Np
6. Plutonium-Pu
7. Americium-Am
8. Curium-Cm
9. Berkelium-Bk
10. Californium-Cf
11. Einsteinium-Es
12. Fermium-Fm
13. Mendelevium-Md
14. Nobelium-No
15. Lawrencium-Lr

From this list, two actinides that are found in abundance in the Earth’s inner layer naturally are Th and U.

Some smaller quantities of Pu and Np can be found in the uranium ores.

Ac and Pa can be found as the decay by-products of some isotopes of Th and U.

The rest of the actinides are said to be synthetic. They are usually found naturally as a part of the decay of the isotope of heavier elements.

Properties of the Actinides

All actinides display the following properties:

• They are radioactive and, therefore, have no stability in variants.
• All actinides are very electropositive.
• Actinide elements are pyrophoric.
• Due to this, they get tarnished in the air readily and change into fine powder.
• All actinide metals are dense and, therefore, possess distinct structures. They can all form several allotropes except Ac, which has lesser crystalline phases.
• Another property of actinides is that they release gas (hydrogen) when they come in contact with water at boiling temperature or diluted acids.
• As actinides are soft, some of them can be split up into pieces using a knife.
• Malleability and ductility are two other properties of actinides.
• Paramagnetism is also a property displayed by the actinides.
• All actinide elements remain hard at normal temperature conditions (room climate) and appear as silver coloured metals.
• Actinides are capable of combining with most non-metals directly.
• The elements of actinides have general placements consecutively in the 5 f-sublevel, and many actinide metals possess characteristics of both f- and d-block substances.
• Actinides, on average, have more valence states than lanthanides, and most of them are susceptible to hybridisation.
• Actinides (An) can be synthesised by reducing AnF3/AnF4 with vapours of Li, Mg, Ca, or Ba at temperatures ranging between 1100°C and 1400°C.

Uses

It is unusual to find radioactive elements in day-to-day life. Some of the instances where we can locate actinides are as follows:

• Americium is used in the sensors that detect smoke.
• Thorium  is used in glass covers.
• Actinium is an indicator that detects the source of Neutron and gamma; it finds its plausible uses in various researches.
• Glass and crystals become luminous through the use of actinides.
• Generally, actinides are used in the production of power and defence operations.
• The actinides are principally used as a source of energy in the atomic reactor and for manufacturing nuclear weapons. Actinides are preferred for the said reactors as they easily become a part of atomic reactions and emit a vast amount of energy. Atomic reactions convert into chain reactions if the conditions are favourable.

Conclusion

Actinides are a group of fifteen elements with atomic numbers ranging between 89 and 103. The first element, Actinium, inspired their name. The actinides are primarily made up of synthetic elements, except uranium and thorium.

The electronic configurations of the actinides are based on the f-sublevel, except for Lawrencium, a d-block element. The periodicity of the elements begins with Actinium or Thorium and continues until Lawrencium.

Actinides are crucial in nuclear reactions as nuclear reactor fuel.