Chemical bond is the attractive force which holds together the constituents atoms or ions or molecules present in a substance.
Co-ordinate Bond.
Atoms form chemical bonds in order to complete their octet i.e. eight electrons in their valence shell.
Ionic bond or electrovalent bond:
"Ionic bond is formed by the complete transfer of one or more electrons from the outermost energy shell of one atom to the outermost energy shell of another atom".
Ex:-
When sodium (Na) and chlorine (Cl) are combined, the sodium atoms each lose an electron, forming cations (Na+), and the chlorine atoms each gain an electron to form anions (Cl−). These ions are then attracted to each other in a 1:1 ratio to form sodium chloride (NaCl).
Factors favouring of Ionic bond:
1)low ionisation energy of the metal atoms.
2)Higher electron affinity of non-metal atoms.
3)Higher value of lattice energy of the resulting Ionic crystals.
4)Large radius of cations and small radius of anions.
5)Large differences of eletronegativity between the combining atoms.
Co-valent Bond:
A covalent bond is a force which binds atoms of same or different elements by mutual sharing of electrons.
Ex:-1:
2:-
Factors favouring covalent bonds:
1)The combining atoms should have small difference in electronegativity.
2)The combining atoms should obtain octate structure by sharing one or more electrons.
3)High electron affinity.
4)Small atomic size.
5)High ionisation energy.
Bond Length:
"The distance between the nuclei of two atoms bonded together is called bond length".
The lengths of double bonds are less than the lengths of single bonds between the same two atoms, and triple bonds are even shorter than double bonds.
Single bond > Double bond > Triple bond (decreasing bond length)
HYBRIDIZATION:
The mixing or merging of dissimilar orbitals of similar energies to form new orbitals is known as hybridisation.
There are many different types of hybridization depending upon the type of orbitals involved in mixing such as sp3, sp2 , sp. sp3d. sp3d2 , etc.
Formation of methane (CH4):
In methane carbon atom acquires sp3 hybrid states as described below:
Here, one orbital of 2s-sub-shell and three orbitals of 2p-sub-shell of excited carbon atom undergo hybridization to form four sp3 hybrid orbitals.
The process involving promotion of 2s-electron followed by hybridization.
As pointed out earlier the sp3 hybrid orbitals of carbon atom are directed towards the comers of regular tetrahedron.
Each of the sp3 hybrid orbitals overlaps axially with half filled Is-orbital of hydrogen atom constituting a sigma bond.
Because of sp3 hybridization of carbon atom, CH4 molecule has tetrahedral shape..
Formation of ethane:
In ethane both the carbon atoms assume sp3 hybrid state.
One of the hybrid orbitals of carbon atom overlaps axially with similar orbital of the other carbon atoms to form sp3-sp3 sigma bond.
The other three hybrid orbitals of each carbon atom are used informing sp3-s sigma bonds with hydrogen atoms.
Each C-H bond in ethane is sp3-s sigma bond with bond length 109 pm. The C-C bond is sp3-sr sigma bond with bond length 154 pm.
Formation of ammonia (NH)3 molecule;
In NH3 molecule the nitrogen atom adopts sp3-hybrid state.
Three of sp3-hybrid orbitals of the N atom are used for forming sp3 (sigma) bonds with H atoms.
The fourth sp3-hybrid orbital carry lone pair of electrons.
The relatively larger lone pair bond pair interactions cause HNH angle to decrease from 109°.281 to 107°.
The ground state, hybrid state of N atom and orbital overlap in are shown in Fig.
Formation of water (H2O) molecule.
In H2O molecule, oxygen atom adopts sp3 hybrid state.
Two of the sp3-hybrid-orbitals of oxygen contains lone pairs of electrons whereas the other two hybrid orbitals constitutesp3-scr (sigma) bonds with H atoms.
The lone pair orbitals exert relatively greater repulsive interactions on bond pair-orbitals causing HOH angle to decrease from 109°.28′ to 104.5°.
The hybridization Of O atom along with orbital overlap in molecule are shown in Fig.
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