Definition of common types of chemical bond
Definition of chemical bond as the force holding together two atoms or groups of atoms forming an aggregate of ions or molecular species by lowering of energy. Ionic, covalent, and metallic are types of common bond.
But the fundamental questions in study chemistry since the beginning to study the forces responsible for the formation of the chemical bonds.
After nearly a century of confusion, Kekul, Van’t Hoff, Le Bel, Lewis, and London, etc in the nineteenth century given the concept of the chemical bonding.
It was easily realized that the number of atoms or groups of atoms combines to form the ions or molecules. Thus every element has a saturation capacity for the formation of chemical bonds. The valency commonly used for the saturation capacity of an element for forming the bonding.
Ionic, covalent, and metallic bond
For study different types of force holding together on atoms or ions, the chemical compound form mainly three types of bonds.
- Ionic, electrovalent, electrostatic
These three bond types represent three types of forces between atoms. But there many chemical compounds whose properties indicate the bond with intermediate types.
Ionic bond definition with example
The ionic bond is thus electrostatic forces that bind together oppositely charged ions. It formed by the transfer of electron or electrons from an electropositive metal to an electronegative non-metal atom.
Electropositive elements have a tendency to lose one or more electrons. But electronegative elements have a tendency to gain electrons.
Formation of ionic bond in sodium chloride
Crystallographic studies show that there is no discrete sodium chloride. Hence in sodium chloride crystal, each sodium ion surrounded by six chlorine atom or vice versa.
These two oppositely charged ions held together by the electrostatic force of attraction. Each sodium atom loses one electron to form uni positive sodium ion. But chlorine atom gains this electron to form uni negative ion. Thus these two ions formed a close-packed crystalline sodium chloride molecule.
Na → Na+ + e
Cl + e → Cl–
Na+ + Cl– → NaCl
Covalent bond definition and example
A covalent bond may be defined as a force holding together atoms through the sharing of electrons.
We easily understand the formation of an ionic bond by electrostatic attraction between two oppositely charged ions. But much difficulty in understanding covalent bonding. Formation of the bond between two hydrogens or two chlorine atoms easily understands. Because there is no electronegativity difference between two identical atoms.
But electron transfers more reasonable when two atoms with wide differences in electronegativity. Thus HF forms by ionic bond because the electronegativity of H and F are different.
The properties of HF differ from the characteristic of the ionic compounds. HF is a nonconductor of electricity and a low boiling point.
Lewis suggested that such covalent compounds formed by the sharing of electrons between the atoms and each atom can attain a noble gas electron configuration.
|Fluorine||1S2 2S2 2P5|
Thus hydrogen attains helium and fluorine attain neon electron configuration.
Coordinate covalent bond definition
But the sharing of electrons equal to the partner not common for the formation of a covalent bond sometimes.
For the formation of the bond between BF3 and NH3, both the electrons come from NH3. Hence such type of bond is called a coordinate covalent bond. So here NH3 as a donner and BF3 is an acceptor.
Formation of metallic compound
Metals are a good conductor of electricity and thermal energy. It formed a crystalline solid with high coordination numbers of 12 or 14.
But all the atoms in a metal are identical so they can not show ionic properties. Because the ionic compounds are formed between two different atoms.
Covalent bonding also not possible for metal. In covalent molecule much weak Van der Waals force acting between the two atoms. It can not explain the rigidity of the metal atom.
Therefore metallic crystal may be a collection of positive atomic cores in a fluid of mobile electrons. In this electron sea model, the force that binds a metal ion to the mobile electrons is known as the metallic bond.
Properties of metallic bonds
This type of picture easily explains the conductivity and heat conduction in the metal.
- Under the influence of the electric field, the electrons of the metal move through the lattice. Thus metals are the conductor of electricity.
- Heat conduction appears due to motion in electrons. Hence the higher energy transfers some energy to mobile electrons. But these electrons move one atomic core to another. Thus metal is the conductor of heat.
Although most of the properties of the metal can explain by this model but the heat capacity of metals difficult to explain.
Thus covalent, ionic, coordinate, and metallic bond explains most of the common physical and chemical properties of the compounds.