What is Sulphur?
Sulfur, also known as sulphur, is amongst the most reactive elements that are present in the periodic table. It is essentially a non-metal which belongs to group 16 (VI A) of the periodic table. The atomic number of sulphur is 16 and it is denoted by S. The element sulphur is a crystalline solid having a bright yellow colour at room temperature. Sulphur is found abundantly in the universe. The sulphur has been used by people since the earlier days and it was known as brimstone which basically means burning stone.
Sulphur Element
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The above image shows the detailed electronic configuration chart of sulphur.
Natural Occurrence of Sulphur
Sulfur or sulphur is the tenth common element of this universe. The creation of 32S takes place in the massive stars where the temperature is more than 2.5 X 109K. It is also present in many types of meteorites in the form of sulphide. The Jupiter moon lo has distinctive colours due to the presence of a sulphur element in several ways in a molten, gaseous and solid-state. On Earth, sulphur is the fifth common element by mass.
Elemental sulphur is generally obtained near the volcanic regions as well as hot springs. In previous times, the primary source of sulphur was Sicily. The submarine volcanoes also lead to the formation of lakes of molten sulphur that is mostly present on the seafloor.
The action of anaerobic bacteria on sulphate minerals like gypsum also leads to the synthesis of native sulphur. Earlier, the commercial production took place by the fossil-based sulphur deposits from gypsum in salt domes. However, this process is currently not the primary source to obtain sulphur for commercial use. Many valuable metal ores like galena, blende, and gypsum are the compounds of sulphur. It is present in the ores in the form of sulphides or sulphates. Natural gas, petroleum and coal also contain sulphur compounds.
Physical Properties of Sulphur
Sulphur is responsible for forming numerous polyatomic molecules. The octa-sulphur is one of the most popular types of molecules associated with sulphur. It is odourless with bright yellow colour and it exists in a soft solid state. The melting point of the molecule is around 115.21° C and its boiling point is about 444.6° C. When the molecule is present between the boiling and melting temperatures, it polymerizes and this leads to lower density but higher viscosity. The depolymerization happens at higher temperatures, which leads to decreased viscosity. The density of sulphur is approximately 2g/cm³, and it might be higher or lower based on allotrope.
Chemical Properties of Sulphur
The burning of sulphur produces a blue flame and an irritating odour due to the formation of sulphur dioxide. Sulphur is insoluble in water but partially soluble in non-polar organic solvents, including benzene. The first ionisation energy of this element is 999.6KJ/mol, and the second is 2252 KJ/mol. The most common oxidation states of this element are +4 and +6. Sulphur is highly reactive and almost reacts with all elements even with the iridium (unreactive metal) except noble gases.
Sulphur compounds have many unusual features as they can exhibit catenation similar to carbon. These properties of sulphur allow it to form chain structures as well as a ring system like the carbon. Hydrogen sulphide (H2S) is one of the most familiar compounds of sulphur. It is a colourless and poisonous gas that has the odour of rotten eggs. It is naturally present in the form of vapours in mineral water and volcanoes. During the removal of sulphur from petroleum, a large amount of hydrogen sulphide is obtained.
Oxygen and sulphur also combine to form various compounds. The most known oxide of sulphur is sulphur dioxide which is a poisonous and colourless gas. It is also used as a reducing agent and bleach in several industries. Scientists also used it to obtain sulphur trioxide. This oxide is also beneficial in fruit ripening and food preservation.
Uses of Sulphur
There are several uses of sulphur. Some of the popular ones are as follows:
Sulphur is an essential element for producing other essential chemicals. The most important chemical produced by sulphur is sulphuric acid which has many industrial applications.
The reaction of sulphur with methane gives carbon disulfide, which is essential for manufacturing rayon and cellophane.
Vulcanization of rubber is another important use of the sulphur element.
Sulphur is one of the crucial components of fertilisers. It is mostly present in fertilisers in the form of a mineral calcium sulphate.
Many pharmaceutical products contain organosulfur compounds. It is also a component in many agrochemicals and dyestuff.
People are using elemental sulphur as pesticides and fungicides from previous times. Dusting sulphur (sulphur in powdered form) is a common pesticide in organic farming.
FAQs on Sulfur
1. What is sulfur and where is it found in nature?
Sulfur, denoted by the symbol S, is a non-metallic chemical element with atomic number 16. It is a bright yellow, crystalline solid at room temperature and is known for its reactivity. Sulfur is the tenth most common element in the universe and is found abundantly on Earth near volcanic regions and hot springs. It also occurs in many minerals, such as gypsum (calcium sulfate), galena (lead sulfide), and as a component of fossil fuels like coal and petroleum.
2. Which group and period does sulfur belong to, and what does this imply about its properties?
Sulfur belongs to Group 16 and Period 3 of the periodic table. Its position in Group 16, also known as the chalcogens or oxygen family, indicates that it has six valence electrons. This configuration makes it highly reactive, as it tends to gain two electrons to achieve a stable octet, commonly forming compounds with an oxidation state of -2. Its non-metallic character and tendency to form covalent bonds are also characteristic of elements in this group.
3. What are the key differences between the two main crystalline allotropes of sulfur?
The two main crystalline allotropes of sulfur are rhombic sulfur (α-sulfur) and monoclinic sulfur (β-sulfur). Their key differences are:
- Structure: Rhombic sulfur has an orthorhombic crystal structure, while monoclinic sulfur has a needle-shaped monoclinic crystal structure.
- Stability: Rhombic sulfur is the most stable form of sulfur at room temperature (below 369 K). Monoclinic sulfur is stable only above 369 K.
- Colour: Rhombic sulfur is pale yellow, whereas monoclinic sulfur is a brighter, amber-yellow.
- Preparation: Rhombic sulfur is formed by evaporating a solution of roll sulfur in CS₂, while monoclinic sulfur is prepared by melting rhombic sulfur and then cooling it slowly.
4. Why does sulfur exist as a stable S₈ puckered ring, while oxygen exists as a diatomic O₂ molecule?
This difference is due to the bonding capabilities of the two elements. Oxygen is small and can form strong pπ-pπ double bonds, resulting in the stable O=O diatomic molecule. Sulfur atoms are larger, and the p-orbital overlap required for strong pπ-pπ bonds is much weaker. Instead, sulfur exhibits a greater tendency for catenation (linking with itself) and forms strong S-S single bonds. This allows it to create a stable, strain-free, eight-membered puckered ring structure (S₈), which is energetically more favourable than a diatomic S₂ molecule.
5. What are the most common industrial applications of sulfur?
The vast majority of sulfur produced is used to manufacture sulfuric acid (H₂SO₄), a critical chemical in many industries. Other significant uses include:
- Vulcanization of rubber: To improve its strength and elasticity.
- Fertiliser production: As a component of phosphate and sulfate fertilisers.
- Chemical manufacturing: To produce carbon disulfide (CS₂), which is used to make rayon and cellophane.
- Pesticides and fungicides: In powdered form ('dusting sulfur') for agricultural use.
6. Explain the unusual change in viscosity when sulfur is heated above its melting point.
When sulfur melts at around 115°C, it forms a low-viscosity liquid of S₈ rings. As the temperature rises above 160°C, these rings break open and form long-chain polymers. These chains entangle with each other, causing a dramatic increase in viscosity, making the liquid thick and dark. If heated further to above 200°C, these long chains begin to break down into smaller units, causing the viscosity to decrease again.
7. Is there a difference between the spellings 'sulfur' and 'sulphur'?
No, there is no chemical difference; both spellings refer to the same element. 'Sulfur' is the official spelling adopted by the International Union of Pure and Applied Chemistry (IUPAC) and is standard in American English. 'Sulphur' is the traditional spelling used in British English. While both are understood, 'sulfur' is the preferred scientific standard worldwide.
8. What is the biological importance of sulfur in living organisms?
Sulfur is an essential element for all life. In the human body, it is a key component of the amino acids methionine and cysteine, which are vital for building proteins and enzymes. These sulfur-containing proteins are crucial for creating strong hair, skin, and nails. Sulfur also plays a role in cellular repair and the function of various enzymes and antioxidants, making it indispensable for metabolic processes.
9. What are the main oxides of sulfur, and what are their environmental impacts?
The two most important oxides of sulfur are sulfur dioxide (SO₂) and sulfur trioxide (SO₃).
- Sulfur dioxide (SO₂): A colourless, pungent gas formed when sulfur burns in air. It is used as a bleach and a food preservative.
- Sulfur trioxide (SO₃): Formed by the oxidation of SO₂. It is a key intermediate in the production of sulfuric acid.
10. Is elemental sulfur harmful to humans?
Elemental sulfur in its pure form has very low toxicity and is generally considered safe to handle with basic precautions. However, many of its compounds are highly toxic and dangerous. For example, hydrogen sulfide (H₂S) is a poisonous gas with the smell of rotten eggs, and sulfur dioxide (SO₂) is a severe respiratory irritant. Therefore, while elemental sulfur itself is not particularly harmful, its compounds can be very hazardous.
