13 Actinium Facts: Details On Discovery, Properties, And Uses

Actinium is the first element of the actinide series in the periodic table.

It is a highly radioactive element and is not present in the natural form of Earth's crust. It can be obtained from uranium ores or created in a nuclear reactor by bombarding radium with neutrons.

According to Rutherford's atomic model, the positive ions called protons and the chargeless ions called neutrons are packed together tightly in a small region called the nucleus. The sum of these neutrons and protons is called the mass number of an element. The negatively charged electrons revolve around this nucleus, just like the planets revolve around the Sun. These electrons are present in their fixed shells or orbits.

The closest shell to the nucleus is called the K shell, which can hold a maximum of two electrons. Following the K shell, there are the next shells: L, M, N, and so on, with higher energy and more electrons. Valence electrons are present on the last shell of the atom. These electrons are highly excited and always try to take up or give away electrons to achieve the electronic configuration of the nearest noble gas and become stable.

Actinium comes with an atomic number 89, which refers to the total number of protons its atoms have. Therefore, actinium has 89 protons in the nucleus of its atom. The total number of protons is equal to the total number of electrons in an atom. This maintains the balance of the electronic charge of an atom and prevents the orbiting electrons from falling into the nucleus of the atom. Thus, the total number of electrons in the atom of actinium is also 89.

It has several isotopes, and the most stable one is actinium 227, which has a half-life of almost 22 years. Its chemical symbol is Ac and has a covalent radius of 215 pm (1 pm = 10−12 m). This element has strong radioactivity, due to which it emits light in the dark. The melting point of actinium is 1922 F (1050 C), while its boiling point is about 5792 F (3200 C). Actinium does not find much uses on the industrial and commercial scale due to its high power of radioactive decay.

Pitchblende of only a single ton consists of 150 mg of actinium. The isotope actinium 228 is part of the thorium decay chain. The price per mCi in US dollar of actinium 225 isotopes is about $800.

Although actinium is very rare and cannot be found naturally, it is not the rarest element. Astatin, having a chemical symbol of At, is considered the rarest element with an atomic number of 85. Other rare elements are osmium, iridium, and rhodium, which occur naturally in the Earth's crust.

Read on to learn more fascinating facts about actinium.

Classification Of Actinium As An Element

Actinium is classified as an actinide, belonging to the actinium series, located just below the lanthanoid series in the periodic table. It has a chemical symbol of Ac and is solid at room temperature. American chemist Glenn Theodore Seaborg was the first person who proposed the concept of the Actinide series in the year 1944. He made his observations regarding the deviations of actinium and other actinide elements in terms of the physical and chemical characteristics of lanthanide series elements.

After its acceptance, a new actinide series was introduced in the modern periodic table, which comprises the elements starting from actinium (89) to lawrencium (103). They were placed just below the lanthanide series. As the partial filling of d subshell is one of the prime features of the transition elements, actinium is also classified as one because its 6d orbitals were filled up.

• Solvent extraction and ion chromatography techniques are used to separate the radioactive metal actinium during its extraction from the uranium ore.
• The oxidation state of actinium is +3, and therefore it is classified as an electropositive element in the periodic table and has an electronic configuration of [Rn]6d17s2 with the presence of three valence electrons in its outermost shell.
• The known actinium compounds are actinium oxide, actinium hydride, and actinium trichloride. The reaction of potassium and actinium trichloride at a temperature of 572 F (300 C) in the production of actinium hydride. Actinium tribromide can be obtained from the reaction of actinium oxide and aluminum bromide. There are about 36 isotopes of actinium, all of which are radioactive elements. Isotopes of an element have a similar mass number but a different atomic number. The chemical reaction of actinium is extremely hazardous, and therefore, all these reactions should always be carried out in a well-protected area with highly designed and equipped laboratories.

Discovery Details Of Actinium

The discovery of actinium dates back to the 19th century. Several other radioactive elements were identified much before the discovery of actinium. This includes the radioactive elements polonium, radon, and radium. However, the isolation of actinium is considered to be the first and the new element with non-primordial radioactivity.

• French chemist Andre Debierne coined the name 'Actinium,' which was discovered in the year 1899 by him. This naming is derived from the Greek word 'aktis' or 'aktinos,' which means 'beam' or 'ray.' This refers to the characteristic glow of actinium due to its radioactivity.
• Many researchers suggest that Andre Debierne worked closely with Marie Curie and Pierre Curie and discovered this metal. According to various sources, it is known that they used a pitchblende sample, from where extractions of polonium and radium were already carried out. Marie Curie discovered this process.
• Again in the year 1902, Friedrich Giesel, a German chemist, independently discovered the actinium. He had not heard of the discovery of actinium by the French chemist, Debierne back at that time. Friedrich Giesel suggested naming the element as 'emanium' due to its ability to 'emit rays.' Actinium fluoride reduction can produce actinium. This reaction needs lithium vapors as a catalyst with an application of high heat of about 2,012-2,372 F (1100-1300 C). Therefore, this reaction is endothermic.

Physical Properties Of Actinium

The physical properties of actinium include its atomic weight to be 227 u, atomic number 89, melting point 1922 F (1050 C), boiling point 5792 F (3200 C), and density 22046 lb per cu m (10 g per cu cm). It belongs to the group of rare earth oxides, which fall under the transition metals group. Its malleability, ductility, and luster are not known. Also, there is no odor from the actinium samples. Flammability and hardness or durability are also unknown to us due to their unavailability in pure form. We get this element primarily by neutron irradiation or by the chemical reaction of certain elements. The first ionization energy is about 664.6 kJ.mol-1, while the second ionization energy of actinium electrons is about 1165.5 kJ.mol-1. Ionization energy is the minimum amount of energy needed to remove an electron from its shell in the atom or molecule. Other physical properties of the elements are described below.

• Actinium has properties similar to the lanthanum, belonging to the lanthanoid group of transition elements. The actinide series are just below the lanthanoid series. Actinium appears to be a silver-colored metal. Sometimes it produces a golden cast.
• Just like other elements of the actinoid series, actinium reacts with atmospheric oxygen and forms a white actinium oxide layer. However, other actinium compounds are not properly known. Another interesting property of actinium is that it appears blue in the dark. This bluish glow results from the ionization of gases by radioactivity in the air.
• Actinium is an extremely dense element, and just like all metals, it is a highly electropositive element that readily forms innumerable allotropes. Allotropy is the property of the elements to exist in multiple forms while they are in the same physical state. For example, the allotropes of carbon are diamond, graphite, and charcoal.
• As it can be found in the uranium ores, actinium becomes readily available by the radioactive decay of uranium and most other radioisotopes, like radium. Since it is not available in free form in the Earth's crust, high purity actinium can be obtained by bombarding radium in a nuclear reactor with neutrons, resulting in radium's radioactive decay. However, a minute quantity of actinium is present in the Earth's crust, which is about 5×10-15%, and its quantity all over the universe is almost negligible. It does not undergo commercial extraction from minerals.

Uses Of Actinium

Actinium is extracted from the uranium ores and rarely occurs in the Earth's crust as a free element. It is mainly produced in laboratories and industries. Due to its scarcity as a free element, the production of actinium in the labs is a costly affair, and therefore, it does not contribute to any significant industrial uses. Furthermore, its radioactive nature makes it toxic to use. The 227 isotope of actinium has a half-life of 21.8 years. It readily decays into thorium 227 or francium 223. The element actinium does not have any significant commercial or industrial applications.

• Actinium is a very important source of alpha rays. However, its usage is limited to the research works in the laboratory.
• Several studies show us that the radioactive property of actinium can actually be used to generate neutrons. Compared to radium, actinium is about 150 times more radioactive, thereby generating a large number of neutrons.
• The radioactive property of actinium can also help treat cancer cells. For example, the treatment of prostate cancer can include actinium as radiation therapy to destroy the metastatic carcinomic cells. Therefore, there are specific uses of actinium in the world of healthcare. Despite its usage in cancer therapy, this actinium metal is considered to be extremely poisonous for the human body. If ingested, it can damage the body cells due to its deposition in bones, liver, and other organs of the body. This can, in turn, cause bone cancer or several other fatal health conditions.