revised Chemistry of s&p block elements including noble gases

Revised Chemistry of s&p block elements including noble gases

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Inorganic Chemistry CONTENTS s-block Elements Group1 Group2 p-block Elements Group13 Group14 Group15 Group16 Group17 Group18 Compounds of Xenon Keywords s- block element, p- block element, general group trend, ionization enthalpy, electro negativity, metallic behaviour, non-metallic behaviour, diagonal relationship, inert pair effect, anomalous behaviour, oxide, hydride, halide, oxo- acid, boron hydride, organometallic compound, boron hydride, silicate, inter halogen, pseudo halogen, noble gas Introduction 1
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The elements in the long form of the periodic table have been divided into four blocks — s, p, d and f- block elements. This classification is based on the type of the atomic orbital in which the outermost electron is located. The s orbital can accommodate two electrons, while the three p orbitals can accommodate a maximum of six electrons. Thus there are two groups of s - block elements — Groups 1 and 2 whose electronic configurations are represented as [Noble gas] ns 1 and [Noble gas] ns 2 respectively. There are six groups of p - block elements — Groups 13 to 18. The s and p block elements are collectively called the main – group elements or representative elements. The d and f - block elements are located between the s and p - block elements. The s - block elements are located on the left of the periodic table and comprise of highly reactive metals. The p -block elements comprise of both metals and non-metals. On moving from left to right in the periodic table the metallic character decreases, while on moving downwards, in a particular group, it increases. Hence it is apparent that we come across both non-metals and metals in p- block elements with metallic character being more apparent in the heavier members of a group. It is more convenient for us to discuss the s and p - block elements separately since the elements in these two blocks differ significantly in their physical and chemical properties. Our main focus will be on general group trends alongwith comparative study of important compounds. I. s - block elements The elements of groups 1 and 2 are called the s- block elements because the outermost electron(s) occupy the s -orbital. They are highly electropositive metals and form ionic compounds. They are referred to as alkali and alkaline- earth metals respectively. Due to their high reactivity the metals do not occur in the free state in nature but are present in form of halides, silicates, nitrates (Group1) and silicates, carbonates, sulphates and phosphates (Group 2). The elements show similarities in physical and chemical properties within a group — however the first elements exhibit considerable differences from the rest of the elements of the same group. This anomalous behaviour is mainly due to the following factors — (i) comparatively higher value of the first ionization energy and electronegativity (ii) small size (iii) high polarizing power of the cation, consequently a greater tendency to form covalent compounds (Fajan’s rules) and complexes, (iii) inability to display a coordination number exceeding 4 due to non-availability of d - orbitals in the valence shell.
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