Bond in Some Homonuclear Diatomic Molecules

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Homonuclear diatomic molecules are molecules composed of two identical atoms bonded together, such as hydrogen (H2), oxygen (O2​), and nitrogen (N2​). These molecules play central roles in nature and display bonding characteristics. These molecules exploring concepts like covalent bonding, molecular orbital theory, and bond order.
Bond in Some Homonuclear Diatomic Molecules-covalent bonding
covalent bonding

Hydrogen Molecule (H2)

Hydrogen is the simplest element, consisting of one proton and one electron. In a hydrogen molecule (H2​), two hydrogen atoms share their electrons through a single covalent bond. The bond is formed by the overlap of the 1s atomic orbitals of each hydrogen atom.
According to molecular orbital theory, the 1s orbitals combine to form two molecular orbitals:
  • A bonding orbital (σ1s​) with lower energy.
  • An antibonding orbital (σ1s​) with higher energy.
In H2​, both electrons occupy the bonding orbital, resulting in a bond order of 1:
Bond Order=Number of bonding electrons – Number of antibonding electrons
                   ————————————————————————
                   
                                                      2
                     =   2- 0
                        ——–   =   1
                            2

This single bond is responsible for the molecule’s stability and low reactivity under normal conditions.

Hydrogen Atom
Bond in Some Homonuclear Diatomic Molecules

Oxygen Molecule (O2)

Oxygen is vital for life, and its molecular form (O2) show a unique bonding structure. Each oxygen atom has six valence electrons, resulting in a total of 12 valence electrons for O2​.
The molecular orbital configuration for O2 is:
σ2s,σ2s∗,σ2pz,π2px = π2py,π2px∗ = π2py∗
The bonding and antibonding orbitals are partially filled, leading to a bond order of 2:
Bond Order = 8−4 / 2 = 2
This indicates a double bond between the oxygen atoms.
O2​ has unpaired electrons in its π∗ orbitals, making it paramagnetic. This property is experimentally confirmed by its attraction to a magnetic field, which molecular orbital theory predicts accurately.

Nitrogen Molecule (N2​)

Nitrogen gas (N2) makes up approximately 78% of Earth’s atmosphere and is known for its exceptional stability. Each nitrogen atom has five valence electrons, leading to a total of 10 valence electrons in the molecule.
Bond in Some Homonuclear Diatomic Molecules-Valence Electron
Valence Electron
The molecular orbital configuration for N2 is:
σ2s,σ2s∗,σ2pz,π2px = π2py,π2px∗ = π2py∗
All bonding orbitals are fully occupied, while the antibonding orbitals remain empty. The bond order is 3:
Bond Order=10−4 / 2 = 3
This triple bond makes N2​ highly stable and inert under normal conditions. The strong triple bond also contributes to the high energy required to break N2​ molecules during chemical reactions.

Halogen Molecules (e.g., Cl2, F2)

Halogens like chlorine (Cl2) and fluorine (F2​) form homonuclear diatomic molecules with a single bond. Each atom contributes one electron to form a covalent bond. For example, in Cl2​:
  • Each chlorine atom has seven valence electrons.
  • The bond order is 1, as only a single bond forms.
Halogen molecules are relatively reactive due to the presence of lone pairs on the atoms, which influence their chemical behavior.

General Trends in Homonuclear Diatomic Molecules

1.Bond Order and Stability: Higher bond orders correspond to stronger and shorter bonds, as seen in N2​ with its triple bond.
2. Magnetic Properties: Molecules like O2​ exhibit paramagnetism due to unpaired electrons, while H2​ and N2​ are diamagnetic.
3. Bond Strength: The strength of the bond decreases as the atomic size increases. For example, the bond in F2 is weaker than in H2 or N2 because of increased electron repulsion in larger orbitals.

Note :-

The bond in homonuclear diatomic molecules provides insights into their stability, reactivity, and properties. These molecules are essential in chemistry and play significant roles in biological and industrial processes.
Homonuclear diatomic molecules consist of two identical atoms bonded together, such as H2​ (hydrogen), O2​ (oxygen), and N2​ (nitrogen). These molecules are formed by the chemical bonding of two atoms of the same element.
In H2, the bond forms when the 1s orbitals of two hydrogen atoms overlap, creating a single covalent bond. The two electrons occupy the bonding molecular orbital (σ1s), resulting in a bond order of 1.
Oxygen (O2​) is paramagnetic because it has two unpaired electrons in its antibonding molecular orbitals
(π 2px∗  and π2py​). This causes it to be attracted to a magnetic field, a property confirmed experimentally.
Nitrogen (N2) is highly stable due to its triple bond, which arises from the sharing of three pairs of electrons. This results in a bond order of 3, making the bond strong and requiring significant energy to break.
Molecular orbital theory explains that the 12 valence electrons in O2 are distributed across bonding and antibonding molecular orbitals. With a bond order of 2, O2​ has a double bond, but the presence of unpaired electrons in antibonding orbitals makes it paramagnetic.
Halogen molecules like Cl2​ and F2​ form single bonds because each atom contributes one electron to the shared pair. This results in a bond order of 1. However, these bonds are weaker compared to molecules like N2​ due to increased repulsion from lone pairs.
Bond order is directly proportional to bond strength and inversely proportional to bond length. Higher bond orders, such as in N2​ (bond order 3), indicate stronger and shorter bonds, while lower bond orders, as in H2​ (bond order 1), correspond to weaker and longer bonds.

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