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Introduction

Chemical Bonding of Class 9

Most of the substances found in nature are in the form of clusters or aggregates of atoms. Any such aggregation in which atoms are held together and which is electrically neutral is called a molecule. The molecules are made of two or more atoms joined together by some force acting between them. The force is termed as a chemical bonds. Thus, a chemical bond is defined as a force that acts between two or more atoms to hold them together as a stable molecule.

Theories on Chemical Bonding

Albrecht Kössel and Gilbert Lewis were the first to explain chemical bond formation in 1916 successfully. They explained chemical bonding based on the inertness of noble gases.

Lewis Theory of Chemical Bonding

  • An atom is the 'Kernel' positively charged (nucleus and internal electrons) and the outer shell.
  • The outer shell can hold only eight electron pairs.
  • The eight electrons in the outer shell take the cube corners around the 'Kernel.'
  • Atoms with an octet configuration, i.e., eight electrons in the outer shell, symbolize stable configuration.
  • Atoms can achieve this stable formation by forming chemical bonds with other atoms. This chemical bond can be formed by the acquisition or loss of electrons (NaCl, MgCl2) or, in some cases, due to electron sharing (F2).
  • Only electrons are present in the outer shell, also known as valence electrons, that participate in forming chemical bonds. Gilbert Lewis used specific notations, better known as Lewis symbols, to represent these electrons in valence.
  • In general, the value of an element may be equal to the number of dots in the corresponding Lewis symbol or eight minus the number of dots (or valence electrons).

Kossel’s theory of Chemical Bonding

  1. The Noble gases that separate halogen is very strong electronegative and alkali metals.
  2. Halogens can form negatively charged ions by receiving an electron. However, alkali metals can form positively charged ions for electron loss.
  3. These ions have a negative charge and well-charged ions with a proper gas formation of 8 electrons in the outer shell. The standard electronic configuration of decent gases (excluding helium) is provided by ns2np6.
  4. As unlike charges are attracted to each other, these differently charged particles are held together by the powerful electrostatic attraction between them. For example, MgCl2, magnesium ion, and chloride ions are bound together by electrostatic attraction. This type of chemical bonding between unlike charged particles is known as an electrovalent bond.

Explanation of Kossel Lewis Approach

In 1916 Kossel and Lewis gave an effective explanation based on the concept of the electronic configuration of noble gases of why atoms combine to form molecules. Atoms of fine gases have little or no contact with other atoms or atoms of other elements. This means that these atoms must have a stable electronic configuration.

Due to the stable configuration, noble gas atoms do not tend to gain or lose electrons. Therefore, their bonding capacity or valency is zero. They are so inert that they do not even form diatomic molecules and exist as gaseous monoatomic atoms.

Types of Chemical bonds

Some important types of chemical bonds are:

  • Ionic or electrovalent bond
  • Covalent bond
  • Dative or Coordinate bond

Atom may attain a stable electronic configuration in three different ways by losing electrons, by gaining, or by sharing electrons.

Elements may be divided into the following three types as

  • Electropositive elements: Whose atom give up one or more electron fairly readily.
  • Electronegative elements: Which will accept electron.
  • Elements that have little tendency to lose or gain electrons.

Three different types of bonds may be formed depending on the electropositive or electronegative character of the atom involved.

Electropositive element + Electropositive element Metallic bond

Electropositive element + Electronegative element →  Ionic bond

Electronegative element + Electronegative element →  Covalent bond.

NCERT Solutions for Class 9 Science prepared by Physics Wallah will help you to solve your NCERT textbook exercise.

Also Check

  1. Metallic Bond
  2. Covalent Bond
  3. Electronegativity
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