Bond Characteristics 

Bond Length

Definition of Bond Length

“The average distance between the centre of the nuclei of

the two bonded atoms is called bond length”.

It is expressed in terms of Angstrom (1 Å = 10–10 m)

or picometer (1 pm = 10–12 m). In an ionic compound, the bond length is the sum of their ionic radii (d = r+ + r–) and in a covalent compound, it is the sum of their covalent radii (e.g., for HCl, d = rH + rCl).

Factors affecting bond length

(i) The bond length increases with increase in the size

of the atoms. For example, bond length of H – X are in the order, HI > HBr> HCl > HF.

(ii) The bond length decreases with the multiplicity of the bond. Thus, bond length of carbon–carbon bonds are in the order, C ≡ C <C = C < C – C.

(iii) As an s-orbital is smaller in size, greater the s-character shorter is the hybrid orbital and hence shorter is the bond length.

For example, sp3 C – H > sp2 C– H > sp C – H

(iv) Polar bond length is usually smaller than the theoretical non-polar bond length.






Bond Angle
Definition of Bond Angle

In case of molecules made up of three or more atoms, the average angle between the bonded orbitals (i.e., between the two covalent bonds) is known as bond angle θ.

Factors affecting Bond Angle

(i) Repulsion between atoms or groups attached to the central atom may increase or decrease the bond angle.

(ii) In hybridisation as the s character of the s hybrid bond increases, the bond angle increases.






 


  

Bond type

  

sp3

  

sp2

  

sp

 

  

Bond angle

  

109º28¢

  

120°

  

180°



(iii) By increasing lone pair of electron, bond angle decreases approximately by 2.5%.



 


  



  

CH4

  

NH3

  

H2O

 

  

Bond angle

  

109º

  

107o

  

105o

 




(iv)  If the electronegativity of the central atom decreases, bond angle decreases.

In case the central atom remains the same, bond angle increases with the decrease in electroneativity of the surrounding atom.

Bond Energy

Definition of Bond Energy

“The amount of energy required to break one mole of bondsof a particular type so as to 

separate them into gaseous atoms is called bond dissociation energy or simply bond energy”.

Greater is the bond energy,stronger is the bond. Bond energy is usually expressed in kJ mol–.

Factors affecting bond energy

(i) Greater the size of the atom, greater is the bond length and less is the bond dissociation energy i.e. less is the bond strength.

(ii) For the bond between the two similar atoms, greater is the multiplicity of the bond, greater is the bond dissociation energy.

(iii) Greater the number of lone pairs of electrons present on the bonded atoms, greater is the repulsion between the atoms and hence less is the bond dissociation energy.

(iv)The bond energy increases as the hybrid orbitals have greater amount of s orbital contribution.     Thus, bond energy decreases in the following order, sp > sp2 > sp3

(v) Greater the electronegativity difference, greater is the bond polarity and hence greater will be the bond strength i.e., bond energy, H – F > H – Cl > H – Br > H – I,

(vi) Among halogens Cl – Cl > F – F > Br – Br > I – I, (Decreasing order of bond energy) Resonance increases bond energy.




References:

1- http://www.newagepublishers.com/samplechapter/000568.pdf