What Are Ionic Compounds

Ionic compounds are normal compounds that doesn’t hold molecules but are composed of ions in a two-dimensional or three-dimensional arrangement. This basic structure is composed of anions and cations and are kept intact within by an ionic bond. The cations are positively charged ions which are usually derived from mettalic elements. Similarly, the anions are the negatively charged which evolve from non-metallic elements.

Ionic Bond:

The understanding of Ionic Bond is important in order to perceive the knowledge of ionic compounds. Kössel and Lewis theory gives a proper insight in the establishment of ionic compounds. This theory is globally used to realize the basics of ionic compounds and the formation of ionic bonds. The theory proposed by Kössel and Lewis is based on two factors. Firstly, realization of the ionization of protons and electrons of a neutral atom to form positive and negative ions respectively. Secondly, the ions settle into a solid arrangement similar to the lattice of the crystalline compound. Elimination of an electron from a neutral atom results in the formation of positive ion. Whereas the inclusion of an electron to a neutral atom results in the formation of negative ion. This was the Kössel and Lewis on the formation of ionic compound along with the establishment of ionic bonds.  

M(g) → M+(g) + e– ;

Enthaply: Ionization and Electron gain Enthalpy

The electron gain enthalpy, which is denoted as ΔegH, is basically a change in the physical property of a neutral atom. It generally relates to the heat content of an atom in thermodynamics. The enthalpy occurs when an atom in its neutral state gains an electron. Liberation of heat or absorption of heat is responsible for the electron gain enthalpy. However, the ionization of neutral atom into a positive ion is always carried out by absorption of heat. This is known as ionization enthalpy.

Ionization enthalpy

X(g) + e– → X – (g)

Electron gain enthalpy

M+(g) + X –(g) → MX(s)

Role of enthalpy in the formation of ionic compounds

Low ionization enthaply or high electron gain enthalpy accelerates ionic compound formation. The cations are usually deduced from metallic elements wheres anions are dervied non-metallic elements. This is commonly seen with every ionic compound formations except the rare formation of Ammonium ion, NH4+, which is derived from two non-metallic elements. 

General structure of Ionic compounds

Generally, ionic compounds thrive in their solid crystalline state. This particular state is composed of both cations and anions in a three-dimensional arrangements, where coulombic interaction energy holds the anions. Factors such as arrangements of cations and anions and size of the ionic compund determines the compund structure after crystallization. The structure of sodium chloride is the best example of such crystalline formation.