Ch 7Elements of Groups 16, 17 and 18 — Class 12 Chemistry, concept-first.

In Std. XI we learnt that in the p-block elements the differentiating electron — the last filling electron — enters the p-orbital of the outermost shell.

Group 16. The elements oxygen (O), sulfur (S), selenium (Se), tellurium (Te) and polonium (Po) constitute Group 16, called the oxygen family.

The general electronic configuration of the group 16 elements is , while that of the group 17 elements is . The group 18 elements are represented by the configuration.

The atomic properties (radii, ionisation enthalpy, electronegativity, electron gain enthalpy) and the physical properties (density, melting and boiling points) of the elements of groups 16, 17 and 18…

These properties are given in Tables 7.2, 7.3 and 7.4.

a. Group 16 elements (Oxygen family or chalcogens) : Oxygen is a gas while the other elements are solids at room temperature.

The first member of each of these groups — oxygen in group 16 and fluorine in group 17 — stands apart from the rest of its family in several properties.

Oxygen shows the following anomalous properties compared to other members of group 16:

Fluorine, the first member of group 17, differs in properties from the other members of the group. The anomalous behaviour of fluorine is due to the following reasons:

The chemical behaviour of the three families follows directly from their valence shell configurations — , and .

i. The group 16 elements have the valence shell electronic configuration . They attain a noble gas configuration either by gaining two electrons, forming ions, or by sharing two electrons, forming two…

i. Group 16 elements : The elements of group 16 react with hydrogen to form hydrides of the type (where E = O, S, Se, Te, Po) — for example , , , and .

i. Group 16 elements : All the elements of group 16 form oxides of the type and , where E = S, Se, Te, Po.

i. Group 16 elements : Elements of group 16 react with halogens to give a large number of halides of the types , and (where E = S, Se, Te).

i. Group 16 elements : Elements of group 16 react with metals to form the corresponding compounds. For example:

Elements of group 16 exhibit allotropy — the existence of an element in two or more forms in the same physical state. Oxygen has two allotropes, and (ozone).

Sulfur exhibits numerous allotropic forms. However, rhombic sulfur (-sulfur) and monoclinic sulfur (-sulfur) are the most important allotropes of sulfur. Table 7.7 compares them property by property.

Both the chalcogens and the halogens form families of oxygen-containing acids — the oxoacids. Sulfur's oxoacids and their structures are taken up first (7.8.1), followed by the oxoacids of the halogen…

Sulfur forms a number of oxoacids. Some of them are unstable and cannot be isolated; they are known to exist in aqueous solutions or in the form of their salts.

Halogens form several oxoacids (see Table 7.8). Only four oxoacids have been isolated in pure form: hypofluorous acid (HOF), perchloric acid (), iodic acid () and metaperiodic acid — printed in the bo…

Oxygen itself, its binary compounds with other elements (the simple oxides), and its triatomic allotrope ozone are the subject of this section: the preparation, properties and uses of dioxygen (7.9.1)…

a. Preparation

A binary compound of oxygen with another element is called an oxide. Oxides can be classified into:

Ozone () is an allotrope of oxygen. Oxygen in the upper atmosphere absorbs energy in the form of ultra-violet light and changes to atomic oxygen, which combines with molecular oxygen to form :

Of sulfur's many compounds, two carry most of the industrial and exam weight: sulfur dioxide — the gas at the heart of both air-chemistry and acid manufacture — and sulfuric acid, the single most impo…

a. Preparation :

a. Preparation : Sulfuric acid is manufactured by the Contact process, which involves the following three steps:

Chlorine — the most industrially important halogen — and its compound hydrogen chloride get their own treatment here: the discovery, preparation, manufacture, properties and uses of chlorine (7.11.1),…

Chlorine was discovered by Scheele, a German Swedish chemist, in 1774, by the action of HCl on . In 1810 Davy established its elementary nature and suggested the name chlorine on account of its colour…

Hydrogen chloride was prepared by Glauber in 1648, by heating common salt with concentrated sulfuric acid. Davy, in 1810, showed that it is a compound of hydrogen and chlorine.

We have seen that all halogen molecules are diatomic. They form binary compounds with hydrogen; with oxygen they form oxoacids; and with other halogens they form interhalogen compounds.

Depending on their composition, interhalogen compounds are classified into four types:

1. The compound is considered as the halide of X. For example, in ClF the halogen having larger size is chlorine — it is more electropositive than F — and hence the interhalogen compound is named as c…

We have studied earlier in this chapter that group 18 elements have very high ionisation energies, and due to this property they are unreactive.

a. Preparation of Xenon Fluorides : Xenon fluorides are generally prepared by the direct reaction of xenon and fluorine, in different ratios and under different conditions — such as temperature, elect…

a. Preparation of Xenon trioxide () : Fluorides of xenon react with water to form .

Xenon forms the following oxyfluorides:

Sample papers and previous-year board questions for this subject.