Chemical Bonding and Compound
Chemical bond meaning the different types of force bonding together by two common atoms or groups of atoms forming an aggregate of ions or molecular species such that there occurs lowering of energy. The definition and formation of chemical bonds or bonding explain the different types of properties like polarity, dipole moment, electric polarization, oxidation number or state, etc of the ionic, covalent, metallic compounds in chemistry or science. But there will be many examples of chemical bonding molecule whose properties and structure indicate the bonds of intermediate types, which are called the coordinate covalent bond.
The fundamental questions in learning chemistry, since the beginning, the forces responsible for the formation of bonds or bonding in the chemical compound. After nearly a century of confusion, Kekule, Van’t Hoff, Le Bel, Lewis, and London, etc in the nineteenth century given the definition of the chemical bonding for learning chemistry. It was easily realized that the number of atoms or groups of atoms combines to form the ions or molecules. Therefore, every chemical compound has a saturation capacity of the electron around the nucleus for the formation of chemical bonding. The Valency is commonly used for the saturation capacity of periodic table elements for chemical bonding.
Different Types of Chemical Bonding
Ionic, covalent, and metallic bonding in crystalline solid metal meaning different types of forces that bonded the atom or ion in a chemical compound. But in coordinate covalent chemical bonding, properties and bonded structure indicate the bond with intermediate types.
Meaning and Definition of Ionic Bond
The electrostatic forces bind together oppositely charged ions in chemical compounds responsible for the formation of ionic bonds. Therefore, the ionic bonding in the molecule is formed by the transfer of electron or electrons from an electropositive metal to an electronegative non-metal atom. Here, electropositive chemical elements have a tendency to lose one or more electron particles. But the electronegative elements have a tendency to gain these electron particles. As a result of mutual electrostatic attraction between positive and negative ion establishes the formation of ionic bonding in chemical compounds.
Examples of Ionic Bonds
Every halogen atom has seven electrons in its outermost orbital. Therefore, the halogen atom gains one electron by chemical bonding to attain the stable electronic configuration of the next inert gas molecule. On the other hand, alkali metal with very low ionization energy has one electron in the outermost orbitals. Therefore, alkali metal tries to lose this electron for the formation of chemical bonding to form a stable noble gas electronic configuration.
From the above idea, Kossel in 1916 developed the theory for the formation of chemical bonding in sodium chloride, potassium chloride, magnesium sulfide, etc. For the formation of NaCl, the sodium atom loses one electron to form a positively charged Na+ ion. But the chlorine atom gains one electron to form a negatively charged Cl– ion.
Na → Na+ + e
Cl + e → Cl–
Na+ + Cl– → NaCl
These two oppositely charged ions associated or bonding together by electrostatic attraction to form sodium chloride crystalline solid molecule. Crystallographic studies of sodium chloride show that there is no discrete sodium chloride molecule in nature. Hence in sodium chloride crystal lattice, each potassium ion is surrounded by six chlorine atoms or vice versa.
Formation of Covalent Bond
G.N. Lewis in 1916 first proposed the formation of chemical bonds in the molecules by atoms without any transference of electrons from one to another. Lewis suggested that the union of atoms by bonding in molecules like hydrogen, nitrogen, oxygen, chlorine, etc, and most of the organic chemical compounds like hydrocarbon, alcohols, organic acids, etc. These types of bonds are formed by the sharing of electrons pair between the atoms. In such a way, the participating atoms complete their octet or form a stable noble gas electron configuration.
For example, the carbon atom has four electrons in the outermost shell. Therefore, the carbon atom needs four electrons to complete the octet. If these four obtained from four chlorine atoms by common sharing, carbon tetrachloride was formed by the covalent chemical bonding. In each bonding, the chemical atom attains its stable inert gas configuration. In the case of the hydrogen atom and carbon atom in methane molecule where hydrogen atom bonding with carbon by sharing of electrons.
Lewis’s theory explains clearly the formation of covalent bonds through the sharing of electrons and also the most chemical behavior like polarity, dipole moment or polarization, etc. of covalent compounds. But the theory does not provide the mechanism of sharing obtained from the learning of wave mechanics.
Examples of Coordinate Covalent Bonds
But the sharing of electrons equal to the partner not common for the definition of covalent chemical bonds sometimes. For the formation of the bond between boron trichloride and ammonia, both the electrons come from ammonia. Hence such type of chemical bonding is an example of a coordinate covalent bond. Therefore, here ammonia acts as Lewis acid, and boron trifluoride act as Lewis base, NH3 + BF3 → F3B←:NH3.
Chemical Bonding in Metallic Compound
Metals are a good conductor of electricity and electric power. Therefore the formation of the metallic bonds given crystalline solid with high coordination numbers of 12 or 14. When the atoms in a metal are identical they can not show ionic properties. Therefore the ionic compounds are formed between two different atoms. Covalent bonds also not possible for metal. In covalent compounds much weak Van der Waals force acting between the two bonding chemical atoms. It can not explain the rigidity of the metal atom.
The metallic chemical bonding may be the collection of positive atomic cores and mobile electrons in the electron sea model. Therefore, the chemical force that binds the metal and mobile electrons responsible for the formation of the metallic bond.
Common Properties of Metallic Bond
The electron sea model in the metallic bond easily explains conductivity and heat conduction in the metal compounds. 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. Therefore, the higher chemical energy transfers some energy to mobile electrons for the formation of metallic bonding. But these electrons move one atomic core to another. Therefore, metal is a good conductor of heat. Although most of the chemical properties of the metal can explain by metallic bonding but the heat capacity of metals difficult to explain by the electron sea model definition.
Formation of Ionic and Covalent Bonding
Therefore, we easy to learning that the ions forming ionic bonding by electrostatic attraction. But not clear that which forces holding the two atoms in the covalent bonds. After the development of quantum mechanics, valence bond and molecular orbital theory explain better the chemical nature of the covalent bonding. Another type of bonding like Hydrogen bond uses for explaining some common physical properties of the compound.