Characteristics of Bond |Bond Length|Bond Enthalpy|Bond Angles

Bond Characteristics

Hello friends welcome to our blog, Today we are going to discuss the various bond characteristics.we know that the chemical bond is possible only if atoms will acquire minimum energy and maximum stability. If it is not having minimum energy than the bond will be very much unstable.

Bond length 

Bond length may be defined as:
                 The average equilibrium distance between the centres of two bonded atoms.

It is also called as Bond distance. The bond length of different covalent bonds are determined by X-Ray diffraction methods.
For covalent bond, It is sum of covalent radii of bonding atoms.For example, Bond length of C-CL bond is cl +  c.
The value of Bond length is expressed in picometre(1 pm=10  -12metre). The various factors such as resonance, electronegativity,hybridization,steric effect etc influence the bond length.

Factor Effect Bond length

1. Size of atoms. The bond length is directly linked with the size of bonding atoms.The bond length of Polar bond is smaller than non polar bond length. For example H-Br bond length(141 pm) is more than H-Cl Bond (127 pm)

2.Multiplicity of bond. The length of double bond(C=C) is less than the length of single bond(C-C) between the same atoms(homo atomic) and the triple bonds(C≡C) even shorter than double bond .

Triple Bond<Double Bond<Single Bond

C≡C            <   C=C               <    C-C

The Multiplicity of the bonds between two atoms brings them close to each other. As a result, the bond length decreases. For example, bond length of C-C bond is 154 pm and the value of C=C bond is 134 pm.

3.Type of hybridisation. The value of  bond length is also influenced by the type of  hybridization.Since s orbital is smaller in size as compared to p orbital,Therefore,greater the s- character smaller will be the bond length.
Example: The alkanes (C-C) have 25% of s character.33.3%  s character  in alkenes(C=C) and
50% as character in alkynes (C≡C).
                   


4.The bond length of same type of two atoms diatomic molecules are twice the covalent radius.

Bond length table

                     Bond Length of Some Common Bonds








Bond Enthalpy

When atoms combine to form bond a certain amount of energy is released.Same amount of energy is needed to break Bond into atoms.Bond enthalpy or bond energy may be defined as

the amount of energy required to break one mole of bond of a particular type in between the atoms in gaseous state of a substance.

Factor Effect Bond Enthalpy

1.The magnitude of bond energy depends upon the type of bonding. Most of the covalent bonds have energy between 50 to 100 kcal per mole.The strength of sigma bond is more than than that of pi bond.

2. If a molecule contains more than one bond of same type, then their bond enthalpy are not same because of the presence of different neighbouring atoms. In such cases, bond enthalpy is the average of bond enthapies of all these bonds.
For example, Cl-Cl Bond enthalpy is 239 kJ per mole while H-H  bond is 433 kJ per mole.

3.If a diatomic molecule contains triple C≡C bond,then it has higher bond energy than that of double bond.Similarly,double bond carbon atoms has higher bond enthalpy than single Bond between the same atoms.

Order

C≡C           >   C=C             >    C-C

4. The bond energy is depend upon the bond length.Shorter the bond length higher is the bond energy

5. The bond energy decreases with the increase in lone pair(lp) on bonded atoms.Electrostatic repulsion of lone pair electrons with  the bonded atoms.

Lp-Lp>Lp-Bp>Bp-Bp

6.Bond energy is also affected by the resonance structured.
Resonance structure. It is a phenomenon of which a molecule expressed in different forms none of which can explain all the properties of molecules.

7.In case of similar molecules bond energy decreases down the group

8. In hybridization the order of energy is

Sp3>sp2>sp>p>s


C H bond energy

The bond dissociation energy of all C-H bonds in methane is not same. Actually when one C-H bond breaks away the electron environment for the remaining C-H Bond change. The carbon atom is now linked with the three C-H bond and not four. Therefore bond dissociation energy changes.

CO bond Energy

The carbon oxygen bond is strongly polarized towards oxygen beacuse  oxygen has much higher electronegative value  than that of carbon.Therefore, the bond length between carbon and oxygen shortens and hence cause the greater bond energy.Bond energy is increasing when going from single to double(CO2) to triple bond(CO)

Bond Angles

Angle between the two adjacent bond of an atom in a molecule made up of three or more atoms is known as bond angle. Bond angle mainly depends upon three factors.

1.Electronegativity. If the central atom is not high electronegative then, bond angle decreases.


2.lone pair repulsive.Lone pair plays a major role in changing the bond angle. If central atom is having lone pair of electrons then the central atom lone pair try to repel the share pair(bonded atoms) of electrons.This is how bonds are slightly displaced inside result in a decrease of bond angle.

3.Hybridization. Bond angle depends upon the state of hybridisation. If the central atom S character increases the hybrid Bond the bond angle increases.



SHARE THIS
Previous Post
Next Post