Chemical Bonding and Molecular Structure Part - 1 | Class 11th

Chapter - 4

Chemical Bonding and Molecular Structure

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Syllabus:

  Ø  Introduction

  Ø  Lewis Dot Structure

  Ø  Valence Electrons

  Ø  Ionic Bond, Covalent Bond

  Ø  Bond Parameters

  Ø  Lewis Structure

  Ø  Polar Character of Covalent Bond

  Ø  Valence Bond Theory

  Ø  Resonance

  Ø  Geometry of Covalent Molecules

  Ø  VSEPR Theory

  Ø  Concept of Hybridization, Involving s, p and d Orbitals and Shapes of Some Simple Molecules

  Ø  Molecular Orbital Theory of Homonuclear Diatomic Molecules (Qualitative Idea Only)

  Ø  Hydrogen Bond.

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It is observed that the atoms of all the elements, except those for noble gases, tend to remain in combined state with the atoms of same or other element. They do not exist as single atoms under ordinary conditions. Such atomic aggregates occur as molecules.

The attractive force that binds the atoms together in a molecule is called a chemical bond. It is formed either by the transfer of electrons or by the sharing of electrons.

The elements with one, two, three, four, five, six or seven electrons is outer shell, use these electrons to complete octet. The electrons which take part in two or more atoms to complete octet is known as Electrovalency.

ü Lewis Dot Structure:  It is a shorthand to represent the valence electrons of an atom. The structures are written as the element symbol surrounded by dots that represent the valence electrons. The inner electrons are well protected and they are called core electrons

 

                                                                                  

ü Octet Rule: This rule was proposed by Lewis and Kossel. According to this rule, atoms undergo chemical reaction in order to attain octet of electrons in the valence shell. Or, atoms containing 8 electrons in their valence shell are stable. To attain octet, they share electrons or exchange electrons.

Furthermore, the atom does this by bonding with each other. Moreover, these atoms can be the same element or with different elements.

Two notable exceptions to the octet rule are helium and hydrogen. This is because both are happy with two electrons belonging in the outer shells.

                  

             

Limitations of Octet Rule:

·       Formation of electron deficient compounds like BeCl₂, BF₃, AlCl₃. Central atom has less than 8e^-.

·       Formation of hypervalent compounds like PCl₅, SF₆, IF₇, H₂SO₄ in which central atom has more than 8 electrons.

·       Formation of compounds of noble gases like XeF₂, XeF₄, XeF₆.

·       Odd electron molecules like NO, NO₂.