Chemical Bonding and Molecular Structure

Bond Parameters

Bond parameters refer to the characterization of covalent bond on the basis of various parameters like bond length, bond angle, bond enthalpy. In this chapter, we will learn more about the concept of bond parameters.

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Different atoms combine all together in order to become stable. By forming bonds, this combination takes place. There are different types of bond, namely, ionic or electrovalent bond, covalent bond, and coordinate bond. This, in turn, shows that every bond has some feature associated with it.

Here are some of the different features or characteristics of bonds which can be termed as bond parameters. A particular covalent bond is characterized by certain parameters:

  • Bond Length
  • Bond Angle
  • The Bond Enthalpy
  • Bond Order

Bond Length

The bond length refers to the distance between the centers of the nuclei of two bonded atoms in an equilibrium position. The stronger the force of attraction in between the bonding atoms, the smaller is the length of the bond. However, the bigger the atom size, the longer the bond length.

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It is measured by spectroscopic, X-ray diffraction and electron diffraction technique. Each atom of the bonded pair contributes to the bond length. In case of a covalent bond, the contribution by each atom is the covalent radius of that atom.

Bond Parameters

The certain factors upon which the bond length is dependent are –

  • Bond Multiplicity: The bond length decreases with an increase in bond multiplicity.
  • Size of an Atom: Bond length is directly proportional to the size of an atom. The bond length increases with the increase in the size of the atoms.

The stronger the force of attraction between the bonding atom, the smaller the bond length.  However, the bigger the size of an atom, the longer will be the bond length. Also, it is to be noted that in the case of a covalent bond, the contribution by each atom is referred to as the covalent radius of that atom.

Download Chemical Bonding Cheat Sheet PDF by clicking on the Download button below

chemical bonding cheat sheet

chemical bonding cheat sheet

Bond Angle

Bond angle refers to the angle between the two bonds i.e. the angle between two orbitals that contains a pair of bonding electron around the central atom in a complex molecule or an ion. This angle is usually measured in degrees, further calculated using the spectroscopic method.

This gives a clear idea about the distribution of bonded electron pairs around the atoms and helps in determination of the shape of the molecules. It also gives an idea about the bonded electron pairs distribution around the atoms and determining the shape of the molecules.

Bond Parameters

Bond Enthalpy

The amount of energy which is needed in order to break one mole of the bond of a particular type between two atoms in a gaseous state is referred to as the Bond Enthalpies. Bond enthalpy is directly proportional to the strength of the bond between the molecules.

In case of polyatomic molecules, the two bonds of the same type can have different bond enthalpy. For e.g.: Two O-H bonds of water molecule have different bond enthalpy. Due to differences in bond enthalpy, polyatomic molecules have average bond enthalpy.

Bond Parameters

Factors affecting the bond Enthalpy:

Bond Order

As per the Lewis description of covalent bonds, the bond order is the number of bonds that forms in between the two atoms in a molecule. The Isoelectronic molecules or ions have the same bond order.

For example, the two isoelectronicc molecules, F2 and O22- are isoelectronic molecules and so have the same bond order of 1. The greater the order of the bond, there is an increase in bond enthalpy and a decrease in the length of the bond.

The bond order in H2 wherein one electron pair is shared is one, in O2 where two electron pairs shared is two and in N2 in which three electron pairs are shared is three.

  • H – H Bond order = 1
  • O = O Bond order = 2
  • N ≡ N Bond order = 3
  • C ≡ O Bond order = 3

Isoelectronic species have the same bond order. For Example, F2, O22- (18 electrons) have bond order 1 N2, CO and NO+ (14 electrons) have bond order = 3

Important Points Regarding the Bond Order

  • The Isoelectronic species,  those species that have the same number of electrons, have equal bond orders. Considering, for example, N2, NO+ and CO have a total of 14 electrons and all of them have the equal bond order of 3.
  • The greater the order of the bond, the greater is the stability of molecules.
  • The greater the order of the bond, the shorter is the length of the bond.

Solved Example For You

Question: Determine the bond order for nitrate ( NO3− ) ion.

Answer :

  1. The Lewis structure of nitrate ion is:
    Bond Parameters
  2. Total number of bonds in the molecule = 4
  3. Total number of bond groups between individual atoms = 3
  4. Hence, the bond order is 4/3 = 1.33
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