SHORT NOTES ON CHEMICAL BONDING

 The process of bond formation is associated with the decrease in energy of the system. This lowest energy state corresponds to the most stable state of the system .Different types of bond formation takes place depending on the nature of the participating atom.

LATTICE ENERGY:- the amount of energy released when the oppositely charged gaseous ions are brought closer from an infinite distance to form one mole of ionic crystal is called lattice energy.

IONIC BOND:-

An ionic bond if formed between 2 atoms which differ much in electronegativities. One atom loses one or more electrons and the other atom gains these electrons ti attain noble gas configuration. the electrostatic force existing between the oppositely charged ions is called an ionic bond.

COVALENT BOND:-

when the elements do not differ much in their electronegativities, transfer of electrons is not possible between the atoms. In this case, sharing of electrons takes place.

"a covalent bond is formed when 2 atoms attain their nearest noble gas configuration by sharing one or more electron pairs. Each of the atom contributes equal number of electrons toward bond formation.

(DID YOU KNOW:-

1. A NON POLAR COVALENT BOND WHEN THE PARTICIPATING ATOMS ARE IDENTICAL OR DO OT DIFFER MUCH IN THEIR ELECTRONEGATIIES.
2. A POLAR COVALENT BOND IS FORMED WHEN THE PARTICIPATING ATOMS HAVE DFFERENT ELECTRONEGATIVITIES. )

SIGMA BOND:-

• it is formed as a result of maximum overlapping of atomic orbitals of s-s ,s-p, and p-p orbitals along the internuclear axes .Due to greater extent of overlapping, this is a strong bond.
• it has an independent existence
• bond dissociation energy is high.
• orbitals s, p and d are capable of forming this bond.
• bonded electron cloud is distributed in a cylindrically symmetrical way around the internuclear axis.

PI BOND:-

• it is a weak covalent bond formed by lateral overlapping of orbitals.
• it does not have an independent existence as it can be formed only after the formation of sigma bond.
• bond dissociation energy is low.
• orbitals other than s are capable of forming this bond.
• bonded electron cloud is distributed in two banana shaped regions above and below the internuclear axis.

HYBRIDIZATION:-

 it is a process of intermixing of two or more atomic orbitals of almost equal energies of an atom and their redistribution into an equal number of identical orbitals. the resultant orbitals are called hybrid orbitals.

VALENCE SHELL ELECTRON PAIR REPULSION THEORY:- 

on the basis of VSEPR theory, the geometry and shapes of covalent molecules can be explained. its postulates are as follows:-

• In polyatomic molecules (i.e. molecules made up of three or more atoms), one of the constituent atoms is identified as the central atom to which all other atoms belonging to the molecule are linked.
• The total number of valence shell electron pairs decides the shape of the molecule.
• The electron pairs have a tendency to orient themselves in a way that minimizes the electron-electron repulsion between them and maximizes the distance between them.
• The valence shell can be thought of as a sphere wherein the electron pairs are localized on the surface in such a way that the distance between them is maximized.
• Should the central atom of the molecule be surrounded by bond pairs of electrons, then, the asymmetrically shaped molecule can be expected.
• Should the central atom be surrounded by both lone pairs and bond pairs of electrons, the molecule would tend to have a distorted shape.
• The VSEPR theory can be applied to each resonance structure of a molecule.
• The strength of the repulsion is strongest in two lone pairs and weakest in two bond pairs.
• If electron pairs around the central atom are closer to each other, they will repel each other. This results in an increase in the energy of the molecules.
• If the electron pairs lie far from each other, the repulsions between them will be less and eventually, the energy of the molecule will be low.

(HERE ARE SOME QUESTION FOR YOU...

1)       FIND OUT WHY CHLORINE EXHIBITS A MAXIMUM COVALENCY OF 7 

2) BOTH HYDROGEN AND BBERYLLIUM HAVE ns2 VALENCE ELECTRONIC CONFIGURATION.HOWEVER , BERYLLIUM FORMS COUMPOUNDS AND HELIUM CANNOT FORM COMPOUNDS.EXPLAIN.

3) WHY IS THE REPULSION BETWEEN TWO LONE PAIR OF ELECTRONS MORE THAN THAT BETWEEN A LONE PAIR AND A BOND PAIR OR A BOND PAIR AND A BOND PAIR OF ELECTRONS. )

CO-ORDINATE COVALENT BOND:-

• it is a special type of covalent bond in which only one of the participating atoms contributes to the electron pair for sharing.
• the atom that gives the electron pair is called donor and the other atom which accepts the electron pair is called an acceptor.
• since contribution is one-sided, a slight polarity develops in the molecule.
• it is also called a dative bond.

(hydrogen bond can only form when hydrogen bonds with oxygen ,fluorine or nitrogen)

(HERE ARE A FEW MORE QUESTIONS FOR YOU...

1. HYDROGEN BONDING IS NOTHING BUT STRONG DIPOLE-DIPOLE ATTRACTION.JUSTIFY
2. WHY DO NH3 AND H2O ACT AS ELECTRON PAIR DONORS
3. BETWEEN VAN DER WAALS FORCES AND DIPOLE DIPOLE ATTRACTION,WHICH ARE STRONGER AND WHY?
4. SOME METALS LIKE SODIUM CAN BE CUT WITH A KNIFE.HOW DO YOU EXPLAIN WITH RESPECT TO METALLIC BOND? )