STD X – CHEMICAL BONDING – EINSTEIN

Introduction

A chemical bond is a lasting attraction between atoms, ions or molecules that enables the formation of chemical compounds. The bond may result from the electrostatic force of attraction between oppositely charged ions as in ionic bonds or through the sharing of electrons as in covalent bonds.

Electrovalent Bond

The concept of chemical bonding was recognised as early as the 12th century that ‘certain types of chemical species were joined by a type of chemical affinity’.

It was only in 1704 that the concept was firmly established by Sir Isaac Newton, when he published the atomic bonding theory. Newton in his statement said, that “particles attract one another by some force, which in immediate contact is exceedingly strong, at small distances performs the chemical operations, and reaches not far from the particles with any sensible effect.”

A chemical Bond is thus defined as the force of attraction that holds various constituents like atoms, ions etc. together. The three main types of bonds that are formed are:

Ionic or electrovalent bonds

Covalent bonds

Co-ordinate covalent or dative bonds

Ionic or Electrovalent Bond

Ionic bonding is the complete transfer of valence electron between atoms. Ionic bonds occur between metals (electron donors) and non-metals (electron acceptors) because of the electrostatic force of attraction between positive and negative ions.

Ionic or electrovalent bonds are formed under the conditions of low ionization energy, high electron affinity and high lattice energy.

Covalent bond

Covalent bonds are formed between two or more atoms when they share electrons. They are normally formed between atoms of similar electronegativity and may occur between atoms of same or of different kind.

Co-ordinate Bond or Dative Bond

A coordinate covalent bond also known as a dative bond or coordinate bond is a type of covalent bond in which the two-shared electrons are supplied by the same atom.

It is formed by two atoms sharing a pair of electrons where one of the atoms has a lone pair of electrons. The electrons are attracted to both the nuclei. The atom which supplies both the electrons is called donor and the other atom is called acceptor.

A lone pair is a valence electron pair without bonding or sharing with other atoms. They are found in the outermost electron shell of an atom.