Study Guides/Chemistry/Bond Order of O2
Study Guide · Chemistry

What is the Bond Order of O2 (Oxygen Gas)?

In chemical bonding, the Bond Order indicates the number of chemical bonds existing between a pair of atoms. A higher bond order means the bond is stronger, shorter, and more stable.

According to both the simple Lewis structure and the advanced Molecular Orbital (MO) Theory, the bond order of the Oxygen molecule (O₂) is 2.

Question (Click to Flip)

What is the bond order of O2?

Answer

The bond order of the O2 molecule is 2, which corresponds to the double bond between the two oxygen atoms.

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Key Facts

Molecule: O₂ (Diatomic Oxygen).

Total Electrons: 16.

Bond Order: 2 (indicates a double bond).

Formula: (Bonding Electrons - Antibonding Electrons) / 2.

Magnetic Nature: Paramagnetic (due to 2 unpaired electrons in antibonding orbitals).

The Simple Lewis Structure Method

An oxygen atom has 6 valence electrons. To achieve a stable octet (8 electrons), two oxygen atoms must share two pairs of electrons with each other. This creates a double bond (O=O). Since there is a double bond connecting the two atoms, the bond order is simply 2.

The Molecular Orbital (MO) Theory Calculation

For competitive exams (like JEE or NEET), you must calculate bond order using MO Theory. Formula: Bond Order = (Number of Bonding Electrons - Number of Antibonding Electrons) / 2

  1. A single Oxygen atom (atomic number 8) has 8 electrons. Therefore, an O₂ molecule has a total of 16 electrons.
  2. We fill these 16 electrons into the molecular orbitals: σ1s², σ1s², σ2s², σ2s², σ2pz², π2px² = π2py², π2px¹ = π2py¹.
  3. Counting the electrons:
    • Bonding electrons (Nb) = 10
    • Antibonding electrons (Na) = 6 (those with the * symbol)
  4. Calculation: Bond Order = (10 - 6) / 2 = 4 / 2 = 2.

Why is Oxygen Paramagnetic?

The MO Theory configuration reveals something the Lewis structure cannot. In the highest energy orbitals (π2px¹ and π2py¹), there are two unpaired electrons. Because of these unpaired electrons, liquid oxygen is actually attracted to a magnetic field. This property is called paramagnetism.

Questions and Answers

What is the bond order of O2?+

The bond order of the O2 molecule is 2, which corresponds to the double bond between the two oxygen atoms.

How do you calculate bond order using MO theory?+

Subtract the number of antibonding electrons from the number of bonding electrons, and divide the result by 2.

Is O2 diamagnetic or paramagnetic?+

O2 is paramagnetic. Molecular Orbital Theory shows that it contains two unpaired electrons in its anti-bonding pi orbitals.

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