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Bond Characteristics 

1. Bond Length

The distance between the nuclei of two atoms bonded together is termed as bond length or bond distance. It is expressed in angstrom (Å)  units or picometer (pm).

[1Å = 10–8 cm; 1 pm = 10–12 m]

Bond length in ionic compound = rc+ + ra 

Similarly, in a covalent compound, bond length is obtained by adding up the covalent (atomic) radii of two bonded atoms.

Bond length in covalent compound (AB) = rA + rB

The factors such as resonance, electronegativity, hybridization, steric effects, etc., which affect the radii of atoms, also apply to bond lengths.

Important features of bond length

  1. The bond length of the homonuclear diatomic molecules are twice the covalent radii.

  2. 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)

  3. Bond length decreases with increase in s-character since s-orbital is smaller than a p – orbital. 
    C – H = 1.112Å:                    spC – H = 1.103Å;                   sp C – H = 1.08Å;                                                 
    (25% s-character as in alkanes) (33.3% s-character as in alkenes) (50% s-character as in alkynes)

  4. Bond length of polar bond is smaller than the theoretical non-polar bond length.

2. Bond Energy or Bond Strength

 Bond energy or bond strength is defined as the amount of energy required to break a bond in molecule.  

Important features of bond energy 

  1. The magnitude of the bond energy depends on the type of bonding. Most of the covalent bonds have energy between 50 to 100 kcal mol–1 (200-400 kJ mol–1). Strength of sigma bond is more than that of a π-bond.

  2. A double bond in a diatomic molecules has a higher bond energy than a single bond and a triple bond has a higher bond energy than a double bond between the same atoms. C ≡ C > C = C > C – C (decreasing bond length)

  3. The magnitude of the bond energy depends on the size of the atoms forming the bond, i.e. bond length. Shorter the bond length, higher is the bond energy.

  4. Resonance in the molecule affects the bond energy.

  5. The bond energy decreases with increase in number of lone pairs on the bonded atom. This is due to electrostatic repulsion of lone pairs of electrons of the two bonded atoms.

  6. Homolytic and heterolytic fission involve different amounts of energies. Generally the values are low for homolytic fission of the bond in comparison to heterolytic fission.

  7. Bond energy decreases down the group in case of similar molecules.

  8. Bond energy increase in the following order:
    s < p < sp < sp2 < sp3
    C – C          >         N – N         >          O – O
    (No lone pair)        (One lone pair)              (Two lone pair)

?Refer to the following video for bond length and bond strength of covalent bonds


3. Bond angles

Angle between two adjacent bonds at an atom in a molecule made up of three or more atoms is known as the bond angle.

Bond angles mainly depend on the following three factors:

(i) Hybridization: Bond angle depends on the state of hybridization of the central atom


Bond angle











Generally s- character increase in the hybrid bond, the bond angle increases.

(ii) Lone pair repulsion: Bond angle is affected by the presence of lone pair of electrons at the central atom. A lone pair of electrons at the central atom always tries to repel the shared pair (bonded pair) of electrons. Due to this, the bonds are displaced slightly inside resulting in a decrease of bond angle.

(iii) Electronegativity: If the electronegativity of the central atom decreases, bond angle decreases.

4. Resonance

There may be many molecules and ions for which it is not possible to draw a single Lewis structure. For example we can write two electronic structures of O3.


In (A) the oxygen - oxygen bond on the left is a double bond and the oxygen-oxygen bond on the right is a single bond. In B the situation is just opposite. Experiment shows however, that the two bonds are identical. Therefore neither structure A nor B can be correct.

One of the bonding pairs in ozone is spread over the region of all the three atom rather than associated with particular oxygen-oxygen bond. This delocalised bonding is a type of bonding in which bonding pair of electrons is spread over a number of atoms rather than localised between two.

1038_bonding pair in ozone.JPG

Structures (A) and (B) are called resonating or canonical structures and C is the resonance hybrid. This phenomenon is called resonance, a situation in which more than one plausible structure can be written for a species.

Atoms gain or lose electrons to attain a more stable noble gas - like electron configuration (octet rule). There are two ways in which atoms can share electrons to satisfy the octet rule:

Ionic Bonding - occurs when two or more ions combine to form an electrically-neutral compound

The positive cation "loses" an electron (or 2 or 3)
The negative anion "gains" the electron (or 2 or 3)
The anion steals the electrons from the cation. 

Covalent Bonding - occurs when two or more atoms combine to form an electrically-neutral compound

The electrons are shared between the two atoms. Both atoms don't have charge in the beginning and the compound remains with zero charge.

The chemical activity of an atom is determined by the number of electrons in its valence shell. With the help of concept of chemical bonding one can define the structure of a compound and is used in many industries for manufacturing products in which the true structure cannot be written at all.

Some other examples

(i) CO32– ion


(ii) Carbon-oxygen bond lengths in carboxylate ion are equal due to resonance.

  1237_Carboxylate ion.JPG

(iii) Benzene


(iv) Vinyl Chloride

          2470_Vinyl chloride.JPG

Difference in the energies of the canonical forms and resonance hybrid is called resonance stabilization energy and provides stability to species.

Rules for Writing Resonating Structures

Only electrons (not atoms) may be shifted and they may be shifted only to adjacent atoms or bond positions.
The number of unpaired electrons should be same in all the canonical form.

The positive charge should reside as far as possible on less electronegative atom and negative charge on more electronegative atom.

Like charge should not reside on adjacent atom

The larger the number of the resonating structures greater the stability of species. Greater number of covalency adds to the stability of the molecule.

Example: Out of the following resonating structures for CO2 molecule, which are important for describing the bonding in the molecule and why?

2377_Resonating structures.JPG         

Solution: Out of the structures listed above, the structure (III) is wrong since the number of electron pairs on oxygen atoms are not permissible. Similarly, the structures (II) has very little contribution towards the hybrid because one of the oxygen atoms (electronegative) is show to have positive charge. Carbon dioxide is best represented by structures (I) and (IV).

To read more, Buy study materials of Chemical Bonding comprising study notes, revision notes, video lectures, previous year solved questions etc. Also browse for more study materials on Chemistry here

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