Group 16 Elements for IIT JEE

Properties and Periodic Trends

Oxygen properties differ greatly from other group elements, but they all have 2 outer orbital choices and 4 electrons in p orbitals, usually written as s2p4. Electron configurations for each element are given below:

• Oxygen: 1s2 2s2 2p4

• Sulphur: 1s2 2s2p6 3s2p4

• Selenium: 1s2 2s2p6 3s2p6d10 4s2p4

• Tellurium: 1s2 2s2p6 3s2p6d10 4s2p6d10 5s2p4

• Polonium: 1s2 2s2p6 3s2p6d10 4s2p6d10f14 5s2p6d10 6s2p4

In this group, the trends of their properties are interesting. Knowing the trend enables us to predict how they will react with other elements. Most trends are true for all element groups, and the group trends are mainly due to the size of the atoms and the number of electrons per atom. Trends are described as below:

• In the order of oxygen, sulfur, selenium, tellurium, or polonium, the metallic properties increase. Essentially, polonium is a metal. It was found by M. Curie, who named it after Poland, her home country.

• Electronegativity, ionizing energy and electron affinity decline for the group as atomic weight increases.

• The atomic radii and melting point increases.

• Because of its small size, oxygen differs from sulphur in chemical properties. The O - S differences are more than the differences among other members.

• Metallic character increases down a group, with metallic tellurium classified as metalloid and metal polonium. All this increases the melting point, boiling point, density, atomic radius and ionic radius down the group.

• The energy of ionization decreases in the group. The most common oxidation state is -2; however, Se, Te, and Po can also have sulphur at + 4 and + 6, and + 2, + 4, and + 6.

Oxygen

• Oxygen is a gas that is colourless, odourless and tasteless at room temperature and at 1 atm. It is both the Earth's crust and the human body's most abundant element by mass. As an abundant element in the atmosphere, it is second next to nitrogen.

• Oxygen gas has many commercial uses, typically obtained through fractional distillation. It is used in iron, steel, and other chemicals manufacturing. It is also used as an oxidizer in rocket fuel, medicinal purposes, and petroleum refining for water treatment.

• There are two allotropes of oxygen, O2 and O3. O2 (or dioxygen) is generally the form referred to when discussing the elemental or molecular form because it is the element's most common form. The O2 bond is very strong, and with other elements too, oxygen can form strong bonds. However, compounds containing oxygen are considered more stable than O2 in terms of thermodynamics. The latter allotrope, ozone, is a poisonous pale - blue gas with a strong smell.

• It is a very good oxidising agent, tougher than dioxygen, and can be used in purifying drinking water as a substitute for chlorine without giving the water an odd taste. However, it disappears due to its unstable nature and leaves the water unprotected against bacteria. Ozone is responsible for protecting the Earth's surface from ultraviolet radiation at very high altitudes in the atmosphere; however, it becomes a major component of smog at lower altitudes. The primary oxidation conditions for oxygen are -2, -1, 0, and -1/2 (in O2-), but -2 is the most frequent.

• Oxides are typically called compounds with oxygen in this state of oxidation. It forms oxides, which are mostly ionic in nature, when oxygen reacts with metals. These can dissolve in water and react with hydroxides, which is why they are called basic anhydrides or oxides. Simple molecules with low melting and boiling points are non-metal oxides that form covalent bonds.

• Oxygen compounds are referred to as peroxides in an oxidation state of -1. Na2O2 and BaO2 are examples of this type of compound. The compound is called a superoxide when oxygen has an oxidation state of -1/2, as in O−2.

• There are a wide range of organic and inorganic oxygen-containing compounds such as peroxides and superoxides, and carbonyl-containing compounds such as ketones, carbonates, and anhydrides.

Sulphur

• At room temperature and at 1 atm pressure, sulphur is a solid. Usually it's yellow, tasteless, and almost odourless. It is the 16th most abundantly sourced element in the crust of Earth. It naturally occurs in various forms, including elemental sulphur, sulfides, sulfates and compounds of organosulphur.

• Sulphur has been mined using the Frasch process since the 1890s, which is useful to recover sulphur from underwater or from sand deposits. Sulphur is used in a variety of ways, including vulcanizing rubber and as a fungicide to protect grapes and strawberries.

• Sulphur, more than any other element in the periodic table, is unique in its ability to form a wide range of allotropes. The most common condition is the solid S8 ring because it is the most thermally stable element at room temperature. There are five different forms of sulphur in the gaseous form (S, S2, S4, S6, and S8). Adequate heat must be supplied to convert sulphur between these compounds.

• Sulphur dioxide (SO2) and sulphur trioxide (SO3) are two common oxides of sulphur. When sulphur is combusted in air, sulphur dioxide is formed, producing a toxic gas with a strong smell. Even these two compounds are used in sulphuric acid production, which is used in a variety of reactions.

• Sulphuric acid is among the top chemicals produced in the U.S. and is mainly used in fertilizer manufacturing. Sulphur also has a wide range of oxidizing states, ranging from -2 to + 6. In a compound, it is often the central ion and can easily bind up to six atoms.

• It forms the compound hydrogen sulfide, H2S, a toxic gas that cannot form hydrogen bonds and has a very small dipole moment. It is easy to recognize hydrogen sulfide by its strong odour similar to that of rotten eggs, but this odour can only be detected at low, non-toxic concentrations. This hydrogen reaction epitomizes how oxygen and sulphur act differently despite their common valence electron configuration and common non-metallic properties.

• There are a variety of compounds containing sulphur, many of which are organic. The prefix thio- in front of the name of an oxygen-containing compound means that a sulphur atom has replaced the oxygen atom.

Selenium

• Selenium appears as an amorphous red or black solid, or as a crystalline red or grey structure, the most stable form being the latter.

• It acts as a semiconductor and is thus mostly used in rectifier manufacturing which are devices to convert alternating currents into direct currents.

• Selenium is also photoconductive, meaning that the electrical conductivity of selenium increases in the presence of light.

• It is used in laser printers and copier drums as well. It is also increasingly used in plumbing.

• In nature, selenium is rare to be found in its elementary form; it typically needs to be eliminated through a whole process of refining, usually involving copper.

• The element is toxic in large doses, but it is required by many animals as a crucial micronutrient.

• The enzyme glutathione peroxidase, which destructs lipid-damaging peroxides, contains selenium atoms. It is an essential cofactor in the human body to maintain the thyroid gland function.

• Furthermore, some research has shown a correlation between selenium-deficiency and an increased risk of HIV / AIDS virus contraction.

Tellurium

• Tellurium is the oxygen family's metalloid with a silver-white colour and a metallic luster at room temperature similar to that of tin. Like selenium, photoconductivity is also displayed.

• Tellurium is an extremely rare component and is most frequently found as a gold telluride. In unique combination with copper, lead, and iron, it is often used in metallurgy.

• It is also used in computer solar panels and memory chips. It is non-toxic or carcinogenic; however, when human beings are exposed to tellurium, they develop a smell of garlic on their breath.

Polonium

• Polonium is an extremely rare metal that is radioactive. The element has 33 different isotopes and all the isotopes are radioactive.

• It has two metallic allotropes and exists in a variety of states. It easily dissolves in diluted acids.

• Polonium does not really exist in compounds in nature, but in the laboratory it can form synthetic compounds. It is used as a beryllium alloy to serve as a source of neutron for nuclear weapons.

• Polonium is an element that is highly toxic. The radiation that it emits makes its handling very dangerous.

• When applied at the correct dosage, it can be immediately lethal or cause cancer if chronic radiation exposure occurs. Methods for treating people who've been irradiated with polonium are still under investigation and it's been shown that chelation agents can be used to decontaminate people.