Ionic and Covalent Bonds: Whenever word bond to hear it means to tie something together. Chemical means we cannot separate (irreversible) by physical means. There is an attractive force which keeps two atoms together in a molecule. In the formation of molecules, only electrons present in the outermost shell or valence shell of atom normally participate. The electrons belonging to inner energy shell are mostly not involved in the formation of the bond. Atoms may attain stable electronic configuration in three different ways by losing or gaining electrons by sharing electrons. Ionic and Covalent bonds form to achieve:
A. Minimum Energy and
What are Ionic and Covalent Compounds?
The formation of bonds between atoms may take place in the following two ways depending upon the electronic configuration of the outermost shell of the combining atoms.
- When there is a complete transference of one or more electrons from one atom to another to complete their octets. This mode of bond formation is referred to as an Electrovalent or Ionic bond and the compound formed is called as an ionic compound. The number of electrons lost or gained by an atom is called its electrovalency.
- By the sharing of electrons between two similar or different atoms. The sharing of electrons between the atoms can take place in the following ways.
- (a) Mutual sharing: The two atoms contribute an equal number of electrons for the bond formation. The bond formed by mutual sharing of electrons is referred to as a covalent bond. The number of electrons contributed by an atom for sharing is called its covalency.
- (b) Unmutual sharing: In this case, the two electrons needed for the formation of a bond are contributed by only one of the two atoms. The shared pair of electrons is called a lone pair and the bond so formed is called the coordinate bond.
Properties of Ionic and Covalent Compounds
The Important characteristics of covalent Compounds are given below:
- Crystal structure: Ionic compounds are crystalline solids in which ions are arranged in a certain definite pattern to form a crystal lattice. For example, in case of sodium chloride, each sodium ion is surrounded by six chloride ions and each chloride ion by six sodium ions, thus giving rise to a three-dimensional crystal structure.
- Non-directional character: In ionic compounds, the oppositely charged ions are held together by the electrostatic force of attraction. As charge is distributed symmetrically around the ion. So ionic bond has no direction, each cation is surrounded by a number of anions and vice versa.
- Solubility: “Like dissolves like” is the principle behind the solubility of a compound. Ionic compounds are usually soluble in polar solvents like water but insoluble in non-polar solvents like benzene and ether.
- High melting point and boiling point: Since the ions are held together by a strong electrostatic force of attraction, the large amount of energy is required to separate the ions. So ionic compounds have high melting point and boiling point.
- Ionization: When an ionic compound is dissolved in water, the force of attraction between ions is weekend and thus the ionic compound splits into ions. In other words, ionization of the compound takes place.
- Electrical conductance: Since the ionic compounds ionize in a molten state or in aqueous Solutions, they conduct electricity in solution or in a fused state. However, they do not conduct electricity in solid state.
- Ionic reaction: The reactions of ionic compounds are the reactions of their ions which are very fast.
Must Read: Ionic Bond Examples.
- Physical State: Unlike ionic compounds (which generally exist as solids), the covalent compounds exist in all the three states, viz, solid, liquid and gaseous.
- Crystal Structure: They usually consist of individual molecules rather than crystalline giant structures.
- Electrical conductivity: Since there are no free ions in covalent compounds to conduct electricity, they are bad conductors of electricity. These are nonelectrolytes.
- Melting and Boiling Points. Covalent compounds have low melting and boiling points because the molecules in covalent compounds are held together less rigidly (by weak van der Waal’s forces), than in case of ionic compounds.
- Solubility: Covalent compounds are generally soluble in organic (non-polar or weakly polar) solvents but insoluble in water and other polar solvents.
- Non-ionic reactions: Since these compounds like CH3Cl or CCI4 are molecular in nature and not ionic, their reactions are molecular and proceed at a much slower rate than those of ionic compounds.
- Directional Character and Isomerism: The covalent bond has a directional character, unlike electrovalent bonds. Due to a directional character of the bond, these molecules show isomerism i.e. one molecular formula may represent two or more than two structural formulae called isomers and this phenomenon is called isomerism.
Compare and Contrast Ionic and Covalent Bonds
|Ionic Bond||Covalent Bond|
|It is generally formed of the metals and nonmetals.||The bond is formed between the two nonmetals.|
|The metal atom loses one or more electrons present in its valence shell and these electrons accept by the nonmetallic atom.||Each combining atom must contribute at least one electron to the shared pair.|
|One of the species is cation and the other is an anion. By losing electrons, the metal atom changes to a (positive ion) cation. Similarly, the nonmetal atom gaining the electrons, get a change to a (negative Ion) anion. The oppositely charged ions attract each other.||The combining atoms mutually contribute one, two or three electrons depending upon their requirement the bond formed.This leads the formation of single double and triple bond.|
|Ionic bond possible only when one of the species must have low ionization energy and the other should have high electron affinity.||The electronegativity difference between the two atoms should be less.|
Difference Between Ionic and Covalent Compounds
|Ionic Compounds||Covalent Compounds|
|They are crystalline solids.||They may be solids, liquids or gases.|
|Ionic exist as ions in their crystal lattice. These ions are held by strong electrostatic forces of attraction.||They exist as molecules in their crystal lattice. These molecules are held by weak van der Waals forces.|
|They are soluble in water and are insoluble in organic solvents.||These Compounds are soluble in organic solvent but are insoluble in water.|
|They have high melting and boiling points.||Covalent Compounds have low melting and boiling points.|
|Their reactions are due to ions which are instantaneous.||Their reactions are molecular which are very slow.|
|These Compounds conduct electricity in solution or in a fused state.||They do not conduct electricity in molten state or in their solutions|
Similarities Between Ionic and Covalent Compounds
The similarity between ionic and covalent only exists in exceptions. Ionic Compounds are generally hard. Similarly diamond is a hard solid like ionic compounds. Ionic compounds are the good conductor of electricity. An exception of graphite in a covalent bond is also a good conductor of electricity.
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