Bond Parameters

What Are Bonding Parameters, and How Are They Used?

Several bond properties, such as bond order, bond length, bond energy and bond angle can be used to characterize covalent bonds. Insight into the stability of a chemical complex and the toughness of the chemical bonds that keep its atoms together can be gained by examining these bond characteristics. 

Bond Order 

When describing a covalent bond, the bond order refers to the total number of covalently bound electron pairs that exist between two atoms in the molecule. It can be determined by sketching the Lewis structure of the molecule and tallying the total number of electron pairs that exist between the atoms in the molecule under consideration. 

• The bond order of a single bond is 1. (H-H)
• The bond order of a double bond is 2. (O=O)
• The bond order of a triple bond is 3. (N ≡ N or C ≡ O)
• It is not possible for two atoms to be covalently bound when the covalent bond order is zero (no bond exists).

Examples:

• H−C≡C−H (acetylene), 1 is the the C−H bond order and 3 is the carbon-carbon bond order
• The bond order is 3 in diatomic nitrogen, N≡N

Important Remarks on Bond Order

Equal bond order is observed for isoelectronic species containing the same number of electrons. The higher the bond order the staler the molecules will be. The bond length decreases as the bond order increases.

Bond Order of the Molecular Orbital Theory

• Molecular orbital theory states that the order of a covalent bond is equal to half the difference between the bonding and the antibonding electrons
• Bond Order= (1/2) * (total bonding electrons – total anti bonding electrons ) 

Bond Angle 

The angle between two bonds, i.e. the angle between two orbitals containing a pair of bonding electrons around the central atom in the molecule, is called the bond angle. This angle is usually calculated by spectroscopic methods and is measured in degrees. 

This helps determine the shape of the molecule by providing a clear picture of the distribution of the bonded electron pairs around the atom. It also determines the shape of the molecule by determining the distribution of the bonded electron pairs surrounding the atom.

Bond Enthalpy 

Bond enthalpy measures the amount of energy required to break one mole of a particular type of bond between two atoms in the gaseous state. The strength of intermolecular bonds is directly related to the bond enthalpy. The bond enthalpy of two bonds of the same type in a polyatomic molecule can be different. For example, the enthalpy of the two OH bonds in a water molecule is different. Polyatomic molecules have an average bond enthalpy due to a deviation in the bond enthalpy.

Bond Length 

1. The distance between the nuclei of two chemically bonded atoms in a molecule is measured in bond length. The sum total of the covalent radii of two chemically bonded atoms must equal the bond length between the two atoms. Higher bond orders lead to stronger bonds, which in turn lead to stronger forces of attraction holding atoms together, and vice versa for covalent bonds. These strong forces of attraction result in short bonds.
2. Spectroscopic techniques such as X-ray diffraction and electron diffraction are used for their measurement. The bond length is determined for each atom of the bonded pair. In the case of a covalent bond, the contraction of each atom is its covalent radius. 
3.  The bond length is determined by several factors including.
4. Multiplicity: if the bond multiplicity increases, the bond length decreases. 
5. Size of the atom: as the size of the atoms increases, the bond length becomes longer. 
6. The shorter the bond length the stronger the attraction between the atoms involved. However, the length of a bond is directly proportional to the size of the atom. It is also important to note that in the case of a covalent bond the contraction of each atom is called the covalent radius of the atom.

The Periodic Trend of Bond Length 

The atomic radius of the atoms involved is proportional to the bond length. The periodic trends in the bond lengths of the elements are similar to the periodic trends in the atomic radii of the elements (decreasing over the period and increasing throughout the group).

Bonding Energy and Factors 

The more energy it takes to break a chemical bond, the more powerful it is. Therefore, the bond’s energy can be expressed as follows:

1. Bond energies are inversely proportional to the length of the bond.
2. Bond energies are directly related to the number of bonds present in a molecule.
3. According to the distances between each of the bonding atoms’ atomic radii (since the atomic radius is directly proportional to bond length).
4. The bond energy is also affected by the electronegativities of the atoms involved in the chemical bond.