Inorganic Chemistry

Some New Facets

Ram Charitra Maurya

• Publisher: De Gruyter
• Year: 2021
• ISBN:
  9783110727401
• Edition: 1
• Topic: Sciences physiques
• Subtopic: Chimie

This book covers different aspects of Inorganic Chemistry in terms of 10 Chapters with in-depth and up-to-date coverage. Starting with the VSEPR theory in the first chapter, the book symmetrically presents delocalized p-bonding in polyatomic molecules; structure, bonding and topology of borane and related compounds; synthesis and reactivity of metal clusters and their bonding; some aspects of stability constants of metal complexes; magnetochemistry; mechanism of inorganic reactions; molecular orbital (MO) approach of bonding in transition metals; bonding in organometallic sandwich compounds based on MO approach. Safe and economical inorganic experiments at UG and PG Levels are also presented in the last chapter. At the end, five relevant topics are included as appendices for updating students and faculty members.

Chapter I Valence shell electron pair repulsion (VSEPR) theory: principles and applications

1.1 Introduction

This theory was first formulated by Sidgwick and Powell (1940) based on the repulsions between electron pairs, known as valence shell electron pair repulsion (VSEPR) theory to explain molecular shapes and bond angles of molecules of non-transition elements. Later on Gillespie and Nyholm (1957) developed an extensive rationale (basis/underlying principle) called VSEPR model of molecular geometry.

According to this theory, the shape of a given species (molecule or ion) depends on the number and nature of electron pairs surrounding the central atom of the species.

1.2 Postulates of VSEPR theory: Sidgwick and Powell

The various postulates of this theory are as follows:

1. The unpaired electrons in the valence shell of central atom form bond pairs (bps) with surrounding atoms while paired electrons remain as lone pairs (lps).
2. The electron pairs surrounding the central atom repel each other. Consequently, they stay as far apart as possible in space to attain stability.
3. The geometry and shape of the molecule depend upon the number of electron pairs (bond pair as well as lone pair) around the central atom.
4. The geometrical arrangements of electron pairs with different number of electron pairs around central atom are given in Table 1.1.

Table 1.1:Shapes of the various molecules depending upon the number of shared electrons around the central metal atom.

1.3 Rules proposed by Gillespie and Nyholm

The following rules have been proposed by Ronald Gillespie and Ronald Sydney Nyholm of University College of London to explain the shape of a number of polyatomic molecules or ions.

1.3.1 Rule 1. Spatial arrangement of electron pairs around the central atom of a given molecule/ion

The electron already present in the valence shell of the central atom of the given species plus the electron acquired by the central atom as a result of bonding with other atoms are called the valence shell electrons. Half of this gives the number of electron pairspresent in the valence shell of the central atom of the given species.

Electron pairs present in the valence shell of the central atom occupy localized orbitals which arrange themselves in space in such a way that they keep apart from one another as for as possible. This gives minimum energy and maximum stability to the species. As there can be only one definite orientation of orbitals corresponding to minimum energy, a molecule or ion of a given substance has a definite shape, that is, a definite geometry.

When the central atom in a molecule is surrounded by bonded electron pair only, the molecule will have a regular geometry or shape. The geometry depends on the number of bonded electron pairs as given in Table 1.1.

1.3.2 Rule 2. Regular and irregular geometry: presence of hybrid orbitals containing bond pairs and lone pairs

If...