Concept of Ionic and Covalent Bonds

Introduction

The two or more atoms, ions, or molecules are held together by forming a chemical bond between them to yield a compound. The stability of the compound depends upon the type of bond formed between the two or more atoms, and the type of bond formed varies in strength and properties. Primarily there are four types of chemical bonds: 

• Ionic bonds
• Covalent bonds
• Hydrogen bonds
• Polar bonds

These bonds are formed by the loss, gain, or sharing of electrons between two atoms or molecules. This article provides detailed information about ionic and covalent bonds.

Ionic bonds are formed by the transfer of electrons between atoms/molecules. Here, one atom loses an electron which is gained by another atom. The atom which gains an electron develops a negative charge and is called an anion, and the atom which loses an electron develops a positive charge and is called a cation.

Covalent bonds are a type of chemical bond formed by the sharing of electrons between the atoms/molecules. Carbon-containing compounds (organic compounds) commonly show this kind of chemical bonding. The electron pairs shared by the two atoms extend around the nuclei of atoms, leading to the formation of a molecule.

COVALENT AND IONIC COMPOUNDS 

Chemical compounds are generally classified into ionic and covalent compounds. As a result of the gain or loss of electrons between two or more charged atoms, ionic bonds are formed. Ions of opposite charges react to form ionic compounds (metal reacts with non-metals). Whereas the reaction of two non-metals forms covalent compounds (also called molecular compounds), the elements form a compound by sharing a pair of electrons, resulting in the neutral molecule.

Gilbert N. Lewis, an American physical chemist, in 1916 first described the concept of Covalent bonding. Some examples of covalent compounds include DNA, sucrose, and water.

IONIC BONDS

An ionic bond, also called an electrovalent bond, is a chemical bond formed by electrostatic interaction between two oppositely charged ions. The bond formation occurs between a cation, which is usually metal, and an anion, usually non-metal. Nearly all of the ionic compounds possess a degree of covalent bonding, which means that a purely ionic bond never exists. So, the ionic bond can be defined as a bond with greater ionic character than the covalent character.

In ionic compounds, the electrostatic forces of attraction between opposite charges and repulsion between negative charges orient the ions in such a way that every positive ion becomes surrounded by negative ions. Every negative ion becomes surrounded by positive ions leading to the overall charge of the molecule as neutral. Such substances tend to be hard and non-volatile. The more significant the difference in electronegativity between the two atoms involved in the bonds, the more polar the bond is. Bonds with partial covalent and partial ionic characters are known as polar covalent bonds.

Electronegativity and ionic bonding

• Transfer of valence electrons leads to the formation of ionic bonds.
• This leads to the formation of two ions, one having the positive charge called cations and one having the negative charge called anions.
• The opposite charges lead to solid and attractive forces between the atoms.
• This force is known as an ionic or electrovalent force.
• An ionic bond is formed between atoms with high electronegativity.
• The compound formed by electrostatic attraction between positive and negative ions is called an ionic compound.

Properties of Ionic bond

• Ionic bonds are the strongest of all bonds.
• They are the most reactive of all bonds when in the proper medium.
• These molecules have high melting and boiling points
• The ionic bonded molecules are good conductors of electricity in their molten Or aqueous states.

Example of ionic bond: Formation of Sodium Fluoride (NaF) occurs by attracting oppositely charged ions and transfer of electrons.

COVALENT BONDS

It is a chemical bond where electrons are shared between two atoms; it is sometimes also called a molecular bond. It occurs between non-metal elements when atoms share a pair of electrons. Atoms covalently bond with other atoms to reach the nearest noble gas electron configuration. The elements formed are neither positive nor negative because neither gain nor loss of electrons occurs. 

Types of covalent bonds

Based on several electrons shared, the covalent bond can be classified as:

• Single covalent bond: a single line indicates a single bond between two atoms(i.e.involving, one electron pair).
• Double covalent bond: a double line(=) indicates a double bond (i.e., involving two electron pairs).
• Triple covalent bond: a triple line indicates ≡) a double bond (involving three electron pairs).

Properties of covalent bond

• Covalent bond contains the approx 80 kilocalories per mole
• They rarely break
• They are directional, i.e., the bonded atoms as they showcase specific orientations relative to one another.
• They tend to have very low melting and boiling points.
• Have lower enthalpies of vaporization and fusion.
• Covalent compounds are insoluble in water. 

Examples of molecules having covalent bonding include inorganic substances hydrogen, nitrogen, water, ammonia with all organic compounds.

IONIC BOND vs COVALENT BOND

• An ionic bond is formed between a non-metal and metal, whereas a covalent bond is between two similar electronegative non-metals.
• Ionic bonds have no specific shapes, whereas covalent bonds have a definite shape.
• Ionic bonds have higher boiling and melting points, whereas covalent bonds have low melting points.
• Ionic bonds have a solid state at room temperature, whereas covalent bonds are gaseous or liquid.
• Ionic compounds have high polarity and are less flammable, whereas covalent compounds are highly flammable and have low polarity.
• An example of an ionic bond is Sodium Chloride; an example of a covalent bond is HCl.