It is interesting to note that certain elements behave like oxygen. In other words, these elements exhibit properties and trends similar to those of oxygen. The members of such a collective group are known as Group 16 elements. Let us see the similarities between oxygen and the other members of this group. We shall also understand why oxygen is an important member of this group.
For convenience sake, we can call this group as the chalcogen family. This family consists of elements found in group 16 of the periodic table. It is essential to remember that periodic tables are an arrangement of elements with similar properties. The chalcogen family is placed under the oxygen classification. Now, these chalcogens are considered as the leading group 16 elements. The elements in this group are – oxygen, sulphur, selenium, tellurium, and polonium. Ref Fig.1.
(Image will be added soon)
What are Chalcogens?
Chalcogens is the name given to periodic table group 16 elements or V1. This group consists of oxygen, sulphur, selenium, tellurium, and polonium. When we call them elements, it is essential to note that oxygen is a gas while other group members are solids. Oxygen and Sulphur are available in pure form while other elements occur as ions in metal ores. O and S form oxides and sulphides.
All elements of this group have isotopes with varying stability. The elements of this group and their compounds vary in their toxicity. O and S are essential to all forms of life. Compounds of selenium, tellurium, and polonium can be hazardous. Selenium is a trace element and can cause disorders. Tellurium compounds have not been known to cause a human fatality. Polonium and its compounds are radioactive, extremely toxic, and need to be handled with care.
About Chalcogens
The chalcogens or the oxygen group is placed in column 16 of the periodic table (ref fig 1). It has elements of oxygen, sulphur, selenium, tellurium, and polonium. You may find one more element, livermorium. The chemical symbols for these elements are- O, S, Se, Te, PO, and Lv. The first four elements of this group are known as chalcogens or ore-forming elements. The reason is that a majority of metal ores found in the Earth’s crust are sulphides or oxides.
You know that oxygen is the most freely found element in nature. It forms 20.946 percent of air and 46.6 percent of the world’s mass generally in the form of silicates, carbonates, oxides and sulphates. We need oxygen to breathe.
Group 16 Elements
All group 16 elements are closely related to human life.
(Image will be added soon)
Oxygen – chemical notation of oxygen is O. It is a colourless and odourless gas. We inhale oxygen and exhale carbon dioxide. Trees exhale oxygen. Oxygen combines with many elements to form their oxides.
Sulphur – the chemical symbol for sulphur is S. It is found in combined as well as the isolated state. In seawater, the percentage of sulphur is 0.09. A large amount of sulphur is found in underground deposits.
Selenium is a rare element. Selenium is found in free as well as in combination with heavy metals such as lead, silver, and mercury in some minerals. Selenium is most stable in grey metallic form.
Tellurium is an element that has properties between metals and non-metals. It is one of the rarest stable elements found on earth. It is located in compounds with copper, lead, silver, and gold. Tellurium is also found in a free state.
Polonium is a radioactive element or isotope in the group 16 elements. It has scientific applications for alpha radiations as it is a radioactive element. It is also a rare element.
FAQs on Group 16 Elements
1. Which elements are classified under Group 16 of the periodic table?
Group 16, also known as the oxygen family, consists of the following elements:
- Oxygen (O)
- Sulfur (S)
- Selenium (Se)
- Tellurium (Te)
- Polonium (Po)
- Livermorium (Lv) (synthetic)
These elements are characterised by having six valence electrons and are part of the p-block in the periodic table.
2. What is the significance of the name 'chalcogens' for Group 16 elements?
The name 'chalcogens' is derived from the Greek words 'chalcos' meaning ore and 'gen' meaning former. Therefore, the term literally means 'ore-formers'. This name is significant because the most common metal ores are oxides and sulfides, which are compounds formed with the first two elements of this group, oxygen and sulfur.
3. How does the electronic configuration of Group 16 elements explain their common -2 oxidation state?
The general valence shell electronic configuration for Group 16 elements is ns²np⁴. To achieve a stable, noble gas configuration (ns²np⁶), these elements have a strong tendency to gain two electrons. By accepting two electrons, they form a dinegative anion (E²⁻), thus exhibiting a common and stable oxidation state of -2.
4. Why does oxygen show anomalous properties compared to other elements in Group 16?
Oxygen's behaviour is different from other Group 16 elements like sulfur and selenium primarily due to three reasons:
- Small Atomic Size: Its small size leads to high electronegativity and ionisation enthalpy.
- Absence of d-orbitals: Unlike sulfur and other heavier elements, oxygen cannot expand its octet, limiting its covalency to 2.
- Ability to form pπ-pπ multiple bonds: This allows oxygen to exist as a diatomic molecule (O₂) with a strong double bond, whereas other elements form single bonds and exist as larger molecules (e.g., S₈).
5. What are the general trends in physical properties as we move down Group 16?
As we move down Group 16 from oxygen to polonium, several physical properties show clear trends:
- Atomic and Ionic Radii: Both increase down the group due to the addition of a new electron shell.
- Ionisation Enthalpy: Decreases down the group because the larger atomic size reduces the nucleus's attraction to the valence electrons.
- Electronegativity: Decreases down the group as the atomic size increases.
- Metallic Character: Increases significantly. Oxygen and sulfur are non-metals, selenium and tellurium are metalloids, and polonium is a radioactive metal.
6. How do the allotropes of sulphur, like rhombic and monoclinic, differ from each other?
Both rhombic (α-sulphur) and monoclinic (β-sulphur) are solid allotropes made of S₈ puckered rings. The key difference lies in their crystal structure and thermal stability. Rhombic sulphur has an orthorhombic crystal structure and is stable at temperatures below 369 K (95.6 °C). Above this temperature, it transforms into monoclinic sulphur, which has a needle-shaped monoclinic crystal structure. This temperature is known as the transition temperature.
7. What is the industrial importance of sulphuric acid (H₂SO₄)?
Sulphuric acid is known as the 'King of Chemicals' due to its extensive use across various industries. Its importance includes:
- Manufacturing fertilisers such as ammonium sulphate and superphosphate.
- Use in petroleum refining and metallurgical applications.
- Production of pigments, paints, and dyestuffs.
- Acting as a dehydrating agent in the production of many chemicals.
- Use in lead-acid storage batteries, which are common in automobiles.
8. Why is ozone (O₃) a more powerful oxidising agent than dioxygen (O₂)?
Ozone is a more powerful oxidising agent than dioxygen because it is thermodynamically less stable. Ozone readily decomposes into dioxygen and a highly reactive nascent oxygen atom [O].
O₃ → O₂ + [O]
This single, highly reactive oxygen atom is responsible for ozone's strong oxidising properties, making it much more effective at oxidation than the stable diatomic O₂ molecule.
9. What is a simple mnemonic to remember the elements of Group 16?
A popular and easy-to-remember mnemonic for the Group 16 elements (Oxygen, Sulfur, Selenium, Tellurium, Polonium) is: 'Oh! Style Se Te Po' or 'Old Style Se T-shirt P(h)at-gaya'. This helps students recall the elements in the correct order of increasing atomic number.
