Diatomic molecules - Homonuclear diatomic & bond order

What are Diatomic molecules?

Molecules formed upon the bonding of two same elements are known as homonuclear diatomic molecules. For example dihydrogen (H2), dinitrogen (N2), etc. In this article, we will study the formation of these diatomic molecules, their stability, and other characteristics.

Dihydrogen-MO-Diagram

Some common diatomic molecules:

  1. Hydrogen molecule (H2): Dihydrogen molecule belongs to the family of diatomic molecules, which consists of two hydrogen atoms bonded to each other by a covalent bond. According to the atomic number of hydrogen, it has only one electron in its 1s orbital. The electronic configuration of H2 molecule is given as:
    H2: (σ1s)2
    Bond order =  =  = 1
    Due to the absence of unpaired electrons in the hydrogen molecule, it is diamagnetic in nature.
  1. Lithium molecule (Li2): Lithium molecule belongs to the family of diatomic molecules, which consists of two lithium atoms, bonded to each other by a covalent bond. The electronic configuration of Limolecule is given as:
    Li2: (σ1s)2 (σ*1s)2 (σ2s)2
    Bond order == 1
    Thus the Li2 molecule is stable and is diamagnetic in nature due to the absence of unpaired electrons.
  1. Carbon molecule (C2): Carbon molecule belongs to the family of diatomic molecules, which consists of two carbon atoms, bonded to each other by a covalent bond. The electronic configuration of the Carbon molecule is given as,
    C2 :(σ1s)2 (σ*1s)2(σ2s)2 (σ *2s)2 (π2p2x= π 2p2y)
    Bond order = = 2
    Due to the absence of unpaired electrons, C2 is diamagnetic in nature. Furthermore, due to the presence of four electrons in pi bonding orbitals, the double bond in C2 consists of both pi bonds.
  1. Oxygen molecule (O2): Oxygen molecule belongs to the family of diatomic molecules, which consists of two oxygen atoms, bonded to each other by a covalent bond.The electronic configuration of the Oxygen molecule is given as,
    O2: (σ1s)2 (σ*1s)2 (σ2s)2 (σ *2s)2 (σ2pz) 2 (π2p2x= π 2p2y) (π*2p1x= π*2p1y)
    Bond order = = 2.
    Due to the presence of one unpaired electron, O2molecule should be paramagnetic.
  1. Helium molecule (He2): According to the atomic number of helium, it has two electrons in 1s.The electronic configuration of the helium molecule  according to molecular orbital theory is given as:
    He2: (σ1s)2 (σ*1s)2
    Bond order == 0.
    Thus, He2  molecule is unstable and does not exist.

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Practise This Question

Which one of the following orbital is filled first in case of N2?