Chem Explorers

Selenium: Exploring its Unique Properties and Versatile Applications

Selenium: The Non-Metallic Element with Unique Chemical Properties

Have you ever heard of selenium? It’s a chemical element that is essential for human health and many industrial applications.

In this article, we’ll explore the various chemical properties of selenium and its placement in the periodic table. We’ll also discuss its significance in the food industry, the manufacturing of pigments, and other various uses.

Selenium’s Non-Metallic Character

Selenium is classified as a non-metallic element, meaning it does not have the properties of a metal. It is described as a metalloid because it has some metallic characteristics such as its luster.

However, unlike most metals, selenium has a brittle texture, meaning it easily cracks or shatters when subjected to stress.

In its natural state, selenium is a gray crystalline solid with some resemblance to sulfur.

Like sulfur, selenium has a pungent odor but is less toxic, making it safer for human handling. Selenium’s primary usage is in the making of electronics, including photovoltaic cells.

Presence in Food and Animal Products

Selenium is also found in many food grains, vegetables, and animal products. The primary role of selenium in the human body is to act as an antioxidant, protecting cells from free radical damage and helping to maintain a healthy immune system.

Furthermore, selenium is found in both primary and secondary levels of the food chain. Primary levels are at the bottom of the chain, such as plants that take up selenium from soil and water.

Secondary levels are at the top of the chain, meaning animals eat the plants and accumulate the selenium in their tissues. This accumulation of selenium occurs mostly in fish, but other sources include meat, eggs, and poultry.

Moreover, selenium is an essential nutrient, although the body needs it in very small quantities. The recommended dietary allowance (RDA) for selenium is 55 micrograms per day for adults.

Adequate selenium intake has been linked to overall better health, including heart disease prevention.

Use in Making Pigments for Paints, Plastics, and Ceramics

Aside from its biological role, selenium is also used for manufacturing pigments for paints, plastics, and ceramics.

These pigments come in various shades of orange, red, and brown, giving these materials their distinctive colors. Selena has been found to be an invaluable element in photography, laser technology, and solar-powered cells.

Selenium pigments have unique properties. For instance, selenium oxide has electrical conductivity, which makes it useful in the making of electrical components, including photovoltaic cells.

Selenium sulfide is a useful pigment in making paints and plastics because of its durability and resistance to fading.

Selenium Symbol and its Group in the Periodic Table

The chemical symbol of selenium is Se, and it is located in the 16th group of the periodic table. This group is called the chalcogens, which means ‘ore-forming’, and contains elements with unique properties such as sulfur, oxygen, and the radioactive metalloid polonium.

The name “chalcogen” is derived from the Greek word “chalcos” which means “ore” since many elements in this group occur naturally in ores. The elements in this group have a similar electron configuration, particularly in their outer shell, giving them similar chemical properties.

Elements in the chalcogen group tend to be oxidizers. This means that they have the ability to react with other elements to produce oxide compounds.


Selenium is a versatile chemical element with unique properties that make it invaluable in many industries. It is a non-metallic element that can be found in food grains and animal products, making it an essential nutrient for overall health.

Furthermore, selenium is a key element in the production of pigments used in paints, plastics, and ceramics. Its placement in the periodic table alongside sulfur and tellurium, both important elements in industrial processes, means that selenium shares the same properties as these elements.

Understanding selenium’s role in human health and industry ensures that we can continue to make proper use of it in a sustainable and safe manner.

Selenium Placement in the Periodic Table and its Atomic Properties

Selenium is a fascinating chemical element, both for its chemical and atomic properties. In this article, we’ll explore its placement in the periodic table, i.e., its period and block location, and its unique atomic attributes, including atomic number, atomic weight, electronegativity, and density.

Selenium Period and Block in the Periodic Table

The periodic table is an organized chart of all known chemical elements, ordered by their atomic number and arranged into periods and groups. Selenium, with an atomic number of 34, is positioned in the 4th period of the periodic table, which is under the 3rd period and above the 5th period.

Moreover, selenium is part of the p-block group, along with other important elements like sulfur, phosphorus, chlorine, and argon. The p-block elements are described as non-metals or metalloids, which means they have some metallic characteristics, but they do not conduct electricity like metals do.

This is due to the incomplete occupancy of their valence electron shell.

Furthermore, the position of selenium in the periodic table helps to understand its properties.

Arsenic and bromine are the neighboring elements of selenium in the periodic table. While arsenic is a toxic element used in some industrial processes, bromine is an essential component in the making of fire retardants, pesticides, and pharmaceuticals.

Selenium shares some similarities with both elements, particularly with arsenic, being a metalloid with some metallic properties.

Selenium Atomic Number, Atomic Weight, Electronegativity, and Density

Selenium has unique atomic properties that make it relevant in several fields like medicine, energy, electronics, and technology.

Its atomic number is 34, indicating that the nucleus of the selenium atom is made up of 34 positively charged protons in the nucleus, the same number of electrons in the orbital shells, giving the element its chemical properties. Moreover, its atomic weight is 78.96 u, making it a relatively light element in terms of its weight compared to others.

The electronegativity of selenium is the measure of its tendency to attract electrons in a chemical bond. On the Pauling scale of electronegativity, selenium has a value of 2.55, comparable to the electronegativity of other non-metals, such as nitrogen (3.04) and phosphorus (2.19).

This value indicates that selenium is slightly more electronegative than its neighbors in the periodic table, but less so than some others, like sulfur.

Moreover, selenium’s atomic density is 4.809 gm/cm3, which is higher than most of the lighter elements in the periodic table.

The atomic density is a measure of how closely packed the atoms are in a material. It is derived from the atomic weight and the atomic radius of the element.

The relatively high atomic density of selenium makes it a solid element with a crystal-like texture.

Selenium’s Unique Atomic and Chemical Properties

Selenium’s unique atomic properties play a vital role in its usefulness in various applications.

For instance, selenium is a photoconductive element, which means that it has the ability to convert light into electricity. This property makes it useful in the making of photovoltaic cells, which are critical in solar technology.

Moreover, selenium has a high melting point of 217C, making it useful in high-temperature applications like metallurgy, where it is used to remove sulfur from iron and steel. Furthermore, selenium is a crucial chemical element in medicine because it helps to prevent DNA damage.

Research has also suggested that an adequate intake of selenium can reduce the risk of some cancers, such as prostate and lung cancer, and heart disease.


Selenium is a non-metallic chemical element with unique atomic properties that make it useful in a range of fields. Its placement in the periodic table under Arsencic and before Bromine, in the 4th period, places it among other important elements with unique properties.

Meanwhile, as a p-block element, its incomplete valence electron shell is responsible for its metallic and non-metallic properties. Its atomic weight, atomic number, electronegativity, and density help to understand its properties and significance in various applications, including photovoltaic cells, high-temperature metallurgy, and health.

Selenium: Its Physical Characteristics and Electronic Properties

Selenium is a chemical element which exhibits unique physical and electronic properties. In this article, we will be discussing its melting and boiling point, Van der Waals radius, covalent and ionic radius, as well as its isotopes and electronic shell configuration.

Selenium Melting Point, Boiling Point, Vanderwaals Radius, and Ionic/Covalent Radius

Selenium is a non-metallic element with unique physical properties and exists in several allotropic forms, with the most stable among them being gray selenium. The melting point of selenium is 220.8 C, and its boiling point is 685 C, making it indispensable in high-temperature applications such as pottery, ceramics, paint, and electrodes.

It is a good conductor of electricity and is commonly used in photovoltaic cells to harness solar energy.

Moreover, the Van der Waals radius, which is a measure of the size of an atom when it is not bonded to another atom, of selenium is approximately 190 pm.

The ionic radius of selenium, when it has gained or lost electrons, is 42 pm, and the covalent radius when bonded in a molecule is 120 pm. The exact radii of selenium depend on the nature of the bond formed.

Selenium Isotopes and Electronic Shell Configuration

The atomic number of selenium is 34, implying that the nucleus possesses 34 protons, which are balanced by 34 electrons arranged in its shells surrounding the nucleus. Selenium possesses many isotopes (a total of 30), in which 6 isotopes are stable, namely ^76Se, ^77Se, ^78Se, ^80Se, ^82Se, and ^84Se, while the rest are unstable.

Of these, ^76Se, ^77Se, ^78Se, and ^80Se are the most abundant, with ^76Se being the most common, making up about 9% of the total selenium found in the earth’s crust. The other isotopes are either synthetic or have a half-life of only microseconds.

The radioactive isotopes are used in various scientific applications, such as radioisotope thermoelectric generators and radiotherapy, to mention a few.

The electronic shell configuration of an atom determines its chemical and physical properties.

For selenium, the electronic configuration is 2-8-18-6, with two electrons in the first shell, 8 electrons in the second, 18 electrons in the third and six valence electrons in the fourth. The outermost shell of selenium contains six electrons, giving it a valence of -2, which is responsible for its ability to form a variety of compounds with other elements.

Moreover, selenium can utilize its fourth shell for making covalent bonds and forming diatomic molecules, such as H2Se and Se2, among others. The diatomic form of selenium, Se2, is a nonmetallic element with a reddish-brown color and exists in the vapor state, making it highly volatile.


In conclusion, selenium has unique physical and electronic properties that make it widely utilized in applications such as solar energy, metallurgy, and health-related issues. Its melting point and boiling point make it indispensable in high-temperature processes, while its Van der Waals, ionic, and covalent radii are crucial parameters for determining its bonding behavior.

Its electronic shell configuration and isotopes play a critical role in understanding its chemical and physical properties. The stable and unstable isotopes of selenium are essential in various scientific and industrial applications, while its specific electronic shell configuration is responsible for selenium’s unique chemical behavior, making it relevant in many fields.

Selenium: Ionization Energies, Oxidation States, Electron Configuration, and CAS Number

Selenium, a versatile chemical element, exhibits unique ionization energies, oxidation states, electron configuration, and is distinguished by its CAS number. In this article, we will delve into the details of selenium’s ionization energies, oxidation states, electron configuration, and its CAS number, shedding light on its properties and significance.

Selenium Ionization Energies

Ionization energy refers to the amount of energy required to remove an electron from a neutral atom. Selenium possesses three ionization energies, each representing the energy required to remove successive electrons.

The first ionization energy of selenium is 940.963 kJ mol^-1, which signifies the energy required to remove the outermost valence electron from a neutral selenium atom. This value indicates that selenium has a moderate tendency to lose its first electron.

The second ionization energy of selenium is significantly higher at 2044.52 kJ mol^-1, signifying the energy required to remove the next electron. This higher value reflects the increased stability and stronger hold of the remaining electrons after the first electron is removed.

Finally, the third ionization energy of selenium is even higher at 2973.727 kJ mol^-1, demonstrating the substantial energy required to remove the next electron after the first two electrons have been removed.

Selenium Oxidation States

Oxidation states refer to the collective charge of an atom in a compound or ion. Selenium exhibits a range of oxidation states, with the most common states being -2, +2, +4, and +6.

In the -2 oxidation state, selenium gains two electrons to achieve a stable configuration, forming compounds such as selenides. On the other hand, in the +2 oxidation state, selenium loses two electrons from its outermost shell.

Compounds in this oxidation state include selenites, selenates, and a variety of other selenium compounds. In the +4 oxidation state, selenium loses four electrons, primarily forming compounds like selenic acid and selenites.

Lastly, in the +6 oxidation state, selenium loses six electrons, resulting in compounds such as selenium hexafluoride and selenic acid. These various oxidation states contribute to the versatility of selenium in various chemical reactions and as a component in different compounds.

Selenium Electron Configuration

The electron configuration of selenium explains the arrangement of electrons in its atomic orbitals. Selenium has the electron configuration of 1s^2 2s^2 2p^6 3s^2 3p^6 3d^10 4s^2 4p^4, with a total of 34 electrons distributed among different energy levels and orbitals.

The notation indicates that there are two electrons in the first s-orbital, followed by an additional two electrons in the second s-orbital. In the p-orbitals, there are six electrons in the second energy level (2p^6) and another six electrons in the third energy level (3p^6).

The d-orbitals in the third energy level accommodate ten electrons (3d^10), while the remaining two electrons are found in the fourth energy level (4s^2). The electron configuration reveals selenium’s ability to form covalent bonds and its range of oxidation states, providing a deeper understanding of its chemical reactivity.

Selenium CAS Number

The Chemical Abstracts Service (CAS) number is a unique identifier for chemical substances. Selenium is assigned the CAS number 7782-49-2, which specifically identifies selenium in its elemental form.

This universally recognized number is important in scientific research, manufacturing, and regulatory compliance, as it allows for easy and precise identification of selenium in various contexts.


Selenium, with its distinct ionization energies, oxidation states, electron configuration, and CAS number, is a chemical element of great significance in numerous applications. The ionization energies dictate the ease of removing electrons from a neutral selenium atom, while the oxidation states determine its ability to form compounds with different valences.

The electron configuration provides insights into selenium’s reactivity and bonding behavior. Lastly, the CAS number serves as a unique identifier for selenium, facilitating accurate identification and tracking.

Understanding these properties of selenium enhances our knowledge and utilization of this element in various scientific, industrial, and technological fields. Selenium: Allotropic Forms, Chemical Classification, State at Room Temperature, and Magnetism

Selenium, a non-metallic element, exhibits various interesting properties, including different allotropes, a solid state at room temperature, and paramagnetic nature.

In this article, we will delve into the details of selenium’s allotropic forms, its classification as a non-metallic element, its state at room temperature, and its magnetism.

Selenium Allotropic Forms

Allotropy refers to the ability of an element to exist in multiple forms with different physical and chemical properties. Selenium is known to exhibit three allotropes, namely red, grey, and black selenium.

Each of these allotropes has unique characteristics and structures. Red selenium, also known as crystalline selenium, is the most common form of selenium.

It appears as a red powder or crystalline substance. Red selenium is composed of helical chains of selenium atoms stacked together, giving it a distinctive structure.

It is a semiconducting material with varying electrical conductivity depending on the temperature and pressure. Grey selenium, also known as amorphous selenium, is a less stable form that can be formed by rapid cooling of red selenium or by heating the element at elevated temperatures.

Grey selenium lacks the well-defined crystalline structure of red selenium and has a more disordered arrangement of atoms. Unlike red selenium, it is a poor conductor of electricity.

Black selenium is another allotrope that is formed at high temperatures and can also be obtained by the reaction of selenium with metals such as silver or lead. It is a metalloid with a shiny appearance and has the highest electrical conductivity among the three allotropes.

Black selenium has a layered structure, with selenium atoms arranged in stacked layers.

Chemical Classification of Selenium

Selenium is classified as a non-metallic element and is situated on the right side of the periodic table among the p-block elements. Its position in the periodic table indicates that selenium shares similar chemical properties with other non-metals, such as oxygen, sulfur, and nitrogen.

While selenium possesses some metallic characteristics, such as its lustrous appearance in black selenium, its overall behavior aligns more closely with that of non-metals.

Selenium State at Room Temperature

At room temperature, selenium exists in a solid state. The solid state is the most stable form for selenium under normal conditions.

Red selenium is the most common allotrope found at room temperature. In its solid state, selenium possesses a characteristic texture, depending on the allotrope.

Red selenium appears as a red powder or crystalline substance, while black selenium has a shiny appearance.

Magnetism of Selenium

Selenium is classified as a paramagnetic material, meaning it is weakly attracted to a magnetic field. This paramagnetic nature arises from the presence of unpaired electrons in selenium’s electron configuration.

In the fourth shell of selenium’s electron configuration, there are two unpaired electrons, which contribute to its paramagnetic properties. When exposed to a magnetic field, selenium experiences a small attractive force but does not retain any magnetization once the external field is removed.

This weak response to magnetic fields is due to the tendency of unpaired electrons to align with the external magnetic field. As a paramagnetic substance, selenium finds applications in devices such as magnetic sensors and recording media.


Selenium displays intriguing properties, including its allotropic forms, chemical classification as a non-metallic element, its solid state at room temperature, and its paramagnetic nature. These characteristics contribute to its diverse range of applications, including uses in semiconductors, electronics, and magnetic technologies.

Understanding selenium’s allotropes, state at room temperature, and magnetism enables scientists and researchers to explore its properties and harness its potential in various fields. In conclusion, selenium’s diverse properties, including its allotropic forms, chemical classification as a non-metallic element, solid state at room temperature, and paramagnetic nature, make it a fascinating and versatile element.

Its allotropes, such as red, grey, and black selenium, exhibit unique structures and electrical conductivities. As a non-metallic element in the p-block, selenium shares chemical similarities with other non-metals.

Existing in a solid state at room temperature, selenium displays paramagnetic properties due to its unpaired electrons. Understanding these characteristics is crucial for harnessing selenium’s potential in various fields, including semiconductors, electronics, and magnetic technologies.

Selenium’s significance lies in its versatility and potential impact in diverse scientific and technological applications. FAQs:

1) What are the different allotropes of selenium?

– Selenium exists in three allotropes: red, grey, and black selenium. 2) How is selenium classified in the periodic table?

– Selenium is classified as a non-metallic element, situated in the p-block. 3) What is the state of selenium at room temperature?

– Selenium is in a solid state at room temperature, with red selenium being the most common allotrope. 4) Is selenium magnetic?

– Yes, selenium displays paramagnetic properties, meaning it is weakly attracted to a magnetic field. 5) What are the potential applications of selenium?

– Selenium has a range of applications in semiconductors, electronics, and magnetic technologies due to its unique properties and diverse allotropes.

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