Chemical

Bonding

By: Dr. Akalesh K. VermaAssistant Professor,

Cotton College State University,Assam, Guwahati-01

Email: akhileshverma07@gmail.com

Introduction

Chemical bonding provides the energynecessary to hold two different atomstogether as part of a chemical compound.

Strength of the bond depends on themolecules or atoms involved in theprocess of bond formation.

Types of Chemical Bonding

1. Ionic Bonds

2. Covalent Bonds

3. Hydrogen Bonds

4. Metallic Bonds

Ionic BondsIonic bonding is the complete transfer ofvalence electron(s) between atoms. It is a typeof chemical bond that generates twooppositely charged ions. In ionic bonds, themetal loses electrons to become a positivelycharged cation, whereas the nonmetal acceptsthose electrons to become a negativelycharged anion.

Ionic bonds are generally formed between

metals and nonmetals

Example of Ionic Bond

A classic example of ionic bonding is between Na and Cl. Na is asilvery metal. It has 1 valence electron. Cl is a yellow-green gas,and it needs 1 electron to fill its valence shell. The ions now have

opposite charges and are attracted to each other byelectrostatic forces. They form a crystal with the rock saltstructure.

Covalent Bonds

A type of chemical bond in which thereis mutual sharing of electrons betweentwo atoms is called covalent bond. It isfurther classified into single, double,and triple covalent bond with respect to

mutual sharing of one, two, and threebonds respectively.

Example of Covalent Bond

When two hydrogen atoms get close enough together, theattraction is balanced in both directions and they share theelectrons between them. A covalent bond is made and hydrogengas (H2) is Formed.

Hydrogen Bonds

A hydrogen bond is the attractive forcebetween the hydrogen attached to anelectronegative atom of one molecule and

an electronegative atom of a differentmolecule.

Usually the electronegative atom isoxygen, nitrogen, or fluorine, which has apartial negative charge.

Example of Hydrogen Bond

Each hydrogen atom is covalently bonded to the oxygen via ashared pair of electrons. Oxygen also has two unshared pairs of

electrons. Thus there are 4 pairs of electrons surrounding theoxygen atom, two pairs involved in covalent bonds with hydrogen,

and two unshared pairs on the opposite side of the oxygen atom.Oxygen is an "electronegative“ atom compared with hydrogen.

Metallic Bonds

Metallic bonding is the type of bondingfound in metallic elements. This is theelectrostatic force of attractionbetween positively charged ions anddelocalized outer electrons.

Metallic bonding refers to theinteraction between the delocalizedelectrons and the metal nuclei.

Example of Metallic Bond

As the metal cations and the electrons are oppositely charged,they will be attracted to each other, and also to other metalcations. These electrostatic forces are called metallic bonds,and these are what hold the particles together in metals.

THE PEPTIDE BOND

Proteins are linear polymers composed of amino acids linked together by peptide

bonds.

The chains containing less than 50 amino acids are called “peptides”, while those

containing greater than 50 amino acids are called “proteins”.

Peptide bond is formed by the condensation of the carboxyl group of one amino

acid and the amino group of the second amino acid with the elimination of

water.

• 2 Amino acids – Dipeptide.

• 3 Amino acids –Tripeptide

• 4-10 Amino acids –Oligopeptide

• >50 amino acids --Protein

THE PEPTIDE BOND FORMATION

PHOSPHO-DIESTER BOND

Phospho-diester bonds are central to all life on Earth.

Phospho-diester bonds makeup the backbone of the strandsof nucleic acid. In DNA and RNA,the phosphodiester bond is thelinkage between the 3' carbonatom of one sugar molecule andthe 5' carbon atom of another,deoxyribose in DNA and ribosein RNA. Strong covalent bondsform between the phosphategroup and two 5-carbon ringcarbohydrates (pentoses) overtwo ester bonds.

GLYCOSIDIC BOND

In chemistry, a glycosidic bond or glycosidiclinkage is a type of covalent bond that joins acarbohydrate (sugar) molecule to anothergroup, which may or may not be anothercarbohydrate. Formation of ethyl gluoside :Glucose and ethanol combine to form ethylglucoside and water.

FORMATION OF GLYCOSIDIC BOND

1.

2.

CHEMICAL BONDS AND THEIR IMPORTANCE IN BIOLOGY

Type of Bond Characteristics Biological Importance

CovalentBonding electrons shared between 2

atoms.

This type of bond holds together

the long chains of

macromolecules (DNA, RNA and

Proteins).

Ionic

Complete transfer of electron from one

atom to another. Oppositely charged

atoms attract one another.

Compounds with ionic bonds

split into ions in water. Ions

conduct electricity. Gives

specialized cells (nerve, muscle)

excitable properties.

Hydrogen

Weaker than covalent or ionic bonds.

Formed between a hydrogen covalently

bonded to O or N and a second O or N.

The second O or N may be on the same

molecule or on another nearby

molecule.

Water: makes water molecules

stick together. Responsible for

many of the strange properties of

water.

Proteins: cause protein chains to

spiral and bend, giving unique

shapes.

DNA: hold together the 2 chains

to form the double helix. Allow

chains to "unzip" for replication

and transcription.