The P-Block Elements: Group 16 Elements

Introduction 

The elements of the group 13 – 18 come under the p – block elements. In these elements the last electron enters in the outermost p – orbital. They have ns2np1-6 electronic configuration in valence shell, helium being an exception. These elements show the maximum oxidation state equal to the sum of electrons in the outermost shell or valence shell. Most of the elements of the p – block form covalent compounds although some elements form ionic compounds (such as halogens) and coordination compounds as well. p-block contains elements which are either metals, non – metals or metalloids. p-block elements include the group of halogens and inert gases. First member of each family of the p-block elements is given below in the table with their general electronic configuration and oxidation states. p-block has the most electronegative element which is fluorine. Elements of p-block generally form acidic oxides. Many elements such as C, Si, Ge, O, N etc. also show phenomenon of allotropy. Property of catenation is also shown by many elements.  

We have covered the Boron Family (Group -13 elements), the Carbon Family (Group – 14 elements) and the Nitrogen Family (Group – 15 elements) in another article of p-block elements. In this article, we will cover the Oxygen Family or Group 16 Elements of p-block elements (Class XII, Chemistry). 

Group 16 is the fourth group of p-block elements. The first element of the group is oxygen, that’s why it is also known as the Oxygen Family. 

Group 16 Elements: The Oxygen Family 

Anomalous Properties of Oxygen 

• Oxygen differs from other elements of the group – 16 due to its high electronegative character, small size and high ionization enthalpy. 

• Hydride of oxygen means water molecules form hydrogen bonds due to high electronegative character of oxygen. 

• d- orbitals are not found in the valence shell of the oxygen atom. It limits its covalency to four. While in case of other elements they have d – orbitals and their covalence exceed four. 

Simple Oxides 

What are Oxides? 

An oxide is a chemical compound that contains at least one oxygen atom and one other element. Dianion of oxygen is also called oxide which is represented by O-2. All oxides compounds contain at least one dianion of oxygen. Oxides are generally binary compounds composed of oxygen and another element. 

Examples of Oxides – Al2O3 – Aluminium oxide, CO2 – Carbon dioxide, SO2 – Sulfur dioxide, CaO – Calcium oxide, MgO – Magnesium oxide, Na2O – Sodium oxide etc. 

Classification of Oxides 

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Oxides can be divided into following types on the basis of valency of another element in oxides –

• Simple oxides 

• Mixed oxides 

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Simple Oxides – Simple oxides are made up of one metal or semimetal and oxygen. These oxides carry only that number of oxygen atoms which is allowed by the normal valency of the element or metal. 

Examples of simple oxides – H2O, MgO, CaO, SiO2 etc. 

Mixed Oxides – Mixed oxides are produced when simple oxides combine. These two simple oxides can be of the same metal (element) or different. 

Examples of Mixed oxides – Red lead (Pb3O) is mixed oxide of lead dioxide (PbO2) and lead monoxide (PbO). Another example is ferro-ferric oxide (Fe3O4) which is a mixed oxide of two simple oxides – ferric oxide (Fe2O3) and ferrous oxide (FeO).

Oxides can be Divided into Following Types on the Basis of Metallic Character of another Element in Oxides –

Metallic oxides 

• Basic oxide 

• Amphoteric oxide 

Non-metallic oxide 

• Acidic oxide 

• Neutral oxide 

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Metallic Oxides – Metallic oxides are made of metal and oxygen. These are generally found in nature as minerals. These are formed by oxidation of metals.

Examples of metallic oxide – CaO, MgO, Fe3O4, BaO, ZnO etc. 

These can be classified into following two types –

• Basic oxide 

• Amphoteric oxide 

Basic Oxide – If an oxide reacts with water and forms a base is called basic oxide. Thus, basic oxide on reacting with water gives base. It means if we prepare a solution of basic oxide and water and dip a red litmus paper in it then it turns blue. 

Examples of basic oxides – MgO, CaO, BaO etc. 

Amphoteric Oxide – An amphoteric oxide is that metallic oxide which shows dual behavior. It behaves as an acidic oxide and basic oxide both. It also reacts with both bases as well as acids. 

Examples of Amphoteric oxides – Zinc oxide (ZnO)

When zinc oxide reacts with conc. Sodium hydroxide it acts as acidic oxide while when it reacts with HCl it acts as basic oxide. Reactions are given below –

ZnO + 2H2O + 2NaOH 🡪 Na3Zn[OH]4 + H2

                            Acidic zinc oxide

ZnO + 2HCl 🡪 ZnCl2 + H2O

                                  Basic zinc oxide 

Another example of amphoteric oxide is Al2O3 – aluminium oxide. When it reacts with sulfuric acid it acts as a base while when it reacts with sodium hydroxide it acts as acid. Reactions are given below –

Al2O3 + 3H2SO4 🡪 Al2(SO4)3 + 3H2O

                                             Basic

Al2O3 + 2NaOH 🡪 2NaAlO2 + H2O

                                              Acidic                      Sodium aluminate

Other examples of amphoteric oxides are BeO, SnO etc. 

Non- Metallic oxide – Non - Metallic oxides are formed by non - metal and oxygen. These are generally found in nature as gases such as carbon dioxide. These are formed by oxidation of non - metals. 

Examples of metallic oxide – CO2, SO2, P2O5, CO etc. 

These can be classified into following two types –

• Acidic oxide 

• Neutral oxide 

Acidic Oxides - If an oxide reacts with water and forms an acid is called acidic oxide. Thus, acidic oxide on reacting with water gives base. It means if we prepare a solution of acidic oxide and water and dip a blue litmus paper in it then it turns red. Mostly acidic oxides are oxides of non – metals but some oxides of metals with high oxidation states also possess acidic character. Thus, few metallic oxides such as CrO3, Mn2O7 etc. are also acidic oxides. 

Examples of acidic oxides – SO2, CO2, SO3 etc. 

When sulfur trioxide reacts with water, it forms sulfuric acid. Reaction is given below –

SO3 + H2O 🡪 H2SO4

Neutral Oxide – Neutral oxides are those oxides which neither show acidic properties nor basic properties. They do not form any salt when react with acid or base. 

Examples of neutral oxides – N2O, NO, CO etc. 

Ozone 

Sulphur 

Following are the two important allotropes of Sulphur –

• ɑ – Sulphur (Rhombic sulfur)

• β – Sulphur (Monoclinic sulfur)

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Sulphur Dioxide 

Oxoacids of Sulphur 

Sulphur forms many oxoacids. An oxoacid is an acid that contains oxygen. Oxoacids of sulfur contain oxygen and sulfur. For examples, H2SO3, H2S2O3, H2S2O7 etc. Different oxoacids of sulfur are prepared by different methods. The most commonly used and the most important oxoacid of sulphur is Sulfuric acid. 

Sulphuric acid is an acidic chemical compound with the formula H2SO4. It is widely used in the industries that is why it is called the king of chemicals. Its worldwide production clearly indicates its industrial strength. In the year 2004, its world production was about 180 million tonnes. It is also known as oil of vitriol. It is an odorless, colorless and viscous liquid which is soluble in water. Preparation of sulphuric acid generally involves highly exothermic processes.

Study of the oil of vitriol began in ancient times. It is believed that Muhammad ibn Zakariya al-Razi was the 1st alchemist of Iran who produced sulfuric acid. Then in 17th century German-Dutch Chemist Johann Glauber prepared sulfuric acid by sulfur with potassium nitrate. In 1736, Doctor Joshua Ward used this method for large scale production of sulfuric acid, although it was an expensive method of production. After this many other methods of production of sulfuric acid were also discovered but they were not economically feasible. Then in 1831, British vinegar merchant Peregrine Phillips patented the contact process, in which sulfuric acid is produced by using sulfur dioxide and oleum in presence of vanadium pentoxide as catalyst. This method is more economically feasible than available all other methods and produces concentrated sulfuric acid. It is the current method of producing sulfuric acid in large scale and high concentration required for industrial processes. 

Contact Process for Manufacturing of Sulfuric Acid 

Steps involved in contact process of manufacturing of sulfuric acid are listed below–

• Preparation of sulfur dioxide 

• Oxidation of sulfur dioxide to prepared sulfur trioxide 

• Addition reaction of sulfur trioxide and sulfuric acid to give oleum 

• Dilution of oleum to produce concentrated sulfuric acid 

Preparation of Sulfur Dioxide – In the 1st step sulfur is oxidized or burned to produce sulfur dioxide. Reaction is given below –

S(s) + O2(g) → SO2(g)

Oxidation of Sulfur Dioxide to Prepared Sulfur Trioxide – Sulfur dioxide is oxidized to sulfur trioxide in presence of vanadium pentoxide as catalyst. It is an exothermic reaction which is reversible in nature. the reaction is given below –

2SO2(g) + O2(g) V2O₅ ↔ 2SO3(g)

Addition Reaction of Sulfur Trioxide and Sulfuric Acid to Give Oleum – Sulfur trioxide is absorbed into ~98% sulfuric acid to form oleum which is also known as fuming sulfuric acid. It is an addition reaction. The reaction is given below –

SO3(g) + H2SO4(l) → H2S2O7(l)

                                 Oleum 

Dilution of Oleum to Produce Concentrated Sulfuric Acid – Oleum is diluted with water to form concentrated sulfuric acid. The reaction is given below –

H2S2O7(l) + H2O(l) → 2H2SO4(l)

It should be noticed here that we used 1 mole of sulfuric acid as reactant and produces 2moles of sulfuric acid. 

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