Page 34 - 6273

CONTENTS MODULE 1.3 THE STRUCTURE OF ATOMS AND

MOLECULES, THE CHEMICAL BOND

LECTURE 4. CHEMICAL BONDS.

STRUCTURE OF MOLECULES AND CRYSTALS

PROGRAM QUESTIONS:

4.1 CHEMICAL BOND. GENERAL PROVISIONS

4.2 TYPES OF CHEMICAL BONDS

4.1 Chemical bond. General provisions.

The chemical bond is the result of the interaction of atoms which determines
the stability of molecules or crystals and is accompanied by a decrease in the

energy of the system.
According to the electronic valence theory the chemical bond is formed

because of the redistribution of valence electrons, resulting in a stable electron
configuration of noble gas (octet) (Kossel) due to the formation of ions or common

electron pairs (Lewis). For example, Lewis’ scheme of formation of a hydrogen

molecule and a hydrogen chloride molecule:

The chemical bond is characterized by energy and length. Usually it is

depicted by the dashes that connect the atoms that interact with each other. Each

dash is equivalent to a generalized electron pair: HN, Cl-Cl, N≡N, H-F.

In compounds containing more than two atoms the valence angle is an

important characteristic. It isformed by chemical bonds in the molecule and

reflects its geometry.

34