Home » Chemistry » MO diagram » Molecular orbital diagram (MO) for F2, F2+, F2-, F22+, F22-, and Bond order

Molecular orbital (MO) diagram for F2, F2+, F2-, F22+, F22-, and their bond order

The chemical formula F2 represents fluorine, a pale-yellow gas formed by the combination of two identical halogen atoms of exceptional reactivity and electronegativity in the Periodic Table of Elements.

In this article, we will teach you the step-by-step construction of the molecular orbital (MO) diagram of fluorine (F2) that provides insight into the bond order, bond length, strength, and magnetic properties of the fluorine molecule. You will also learn to draw the MO diagrams of related molecular ions i.e., F2+, F2, F22+, and F22-.

So let’s take a deep dive into this intricate but super fun realm of Chemistry.

Name of molecule

Fluorine

Chemical formula

F2

Electronic configuration

1s2 2s2 2p5

Molecular orbital electronic configuration

(σ1s2)(σ*1s2)(σ2s2)(σ*2s2) (σ2pz2) (π2px2)(π2py2)(π*2px2) (π*2py2)

Number of electrons in bonding MOs

10

Number of electrons in anti-bonding MOs

8

Bond order

1

Paramagnetic or Diamagnetic?

Diamagnetic

 

How to draw the molecular orbital (MO) diagram of F2 with its bond order?

As per the molecular orbital theory (MOT) of chemical bonding, after bond formation, the individual atomic orbitals cease to exist. Rather, the atomic orbitals of constituent atoms combine to form a unique set of molecular orbitals (MOs).

The electrons of the participant atoms are thus held in these MOs, belonging to the entire molecule in unison.

The linear combination of atomic orbitals (LCAO) produces two types of molecular orbitals:

  • Bonding molecular orbitals
  • Anti-bonding molecular orbitals

The number of MOs produced is exactly equal to the number of atomic orbitals coming together.

A bonding molecular orbital is formed by the linear combination of two AOs in the same phase.

Contrarily, an antibonding molecular orbital is produced by the linear combination of two AOs in the opposite phase, counteracting the cohesive forces of the combining nuclei.

formation of bonding and antibonding Molecular orbital diagram (MO) for F2

This is why, a bonding MO always lies at a lower energy (greater stability) than the parent AOs while an antibonding MO occupies an energy level higher than that of parent AOs (higher instability).

The electrons are filled in these MOs following the three simple rules:

  1. Aufbau Principle: Electrons first occupy the lower energy orbitals followed by their placement in the higher energy molecular orbitals.
  2. Hund’s Rule: The incoming electrons are singly filled in the degenerate MOs before pairing occurs.
  3. Pauli Exclusion Principle: Two electrons placed in the same MO exhibit an opposite spin (clockwise and anticlockwise).

The different numbers of electrons present in the bonding and/or antibonding MOs of a molecule are represented in the form of an energy level diagram called the molecular orbital (MO) diagram.

The MO diagram in turn helps in predicting other useful properties of molecules such as their bond order, bond stability, magnetic behavior, etc.

Fluorine (F2) is a homonuclear diatomic molecule. Two identical F-atoms combine to form an F2 molecule.

We can easily draw the Molecular orbital diagram of F2 following the steps given below.

Steps for drawing the molecular orbital (MO) diagram of F2 with its bond order

1. Write down the electronic configuration of F2 atoms

F2 consists of two fluorine (F) atoms.

The electronic configuration of each F-atom is 1s2 2s2 2px2 2py2 2pz1.

Usually, only the valence electrons are displayed in the MO diagram of a molecule, therefore, it is important to note that each F-atom contains 7 valence electrons.

2 F-atoms combined make a total of 18 electrons and 14 valence electrons in F2.

2. Determine whether the molecule is homonuclear or heteronuclear

F2 is a neutral molecule. It is homonuclear as it is formed by two atoms of the same element. Thus the individual AOs of two F-atoms lie at the same energy level.

As per the rule of LCAO, the two 1s atomic orbitals of fluorine overlap to produce two molecular orbitals i.e., a bonding molecular orbital (σ1s) and an antibonding molecular orbital (σ*1s).

Similarly, two 2s atomic orbitals combine to form two MOs, σ2s and σ*2s. Finally, the three 2p atomic orbitals from each F-atom overlap to produce six MOs including three bonding MOs (σ2pz, π2px, and  π2py) and three anti-bonding MOs (π*2px, π*2py, and σ*2pz).

The MOs discussed above are located on the MO diagram in an increasing energy order.

Energy level diagram of F2

3. Fill the molecular orbitals of F2 with electrons following the energy and bonding principles

A total of 4 electrons are present in the 1s atomic orbitals of two fluorine atoms. Therefore, as per the Aufbau principle, the first two electrons go in the lowest energy σ1s MO, and the remaining two are accommodated in σ*1s.

Similarly, the 4 electrons in the 2s atomic orbitals of fluorine, are uniformly distributed between σ2s and σ*2s molecular orbitals of F2.

In contrast, there are a total of 5 + 5 = 10 electrons in the 2p atomic orbitals of two F-atoms. Thus, the first two electrons are placed in σ2pz while the next two are situated in π2px and π2py and consequently paired up.

2 + 2 + 2 = 6 leaves behind 10 – 6 = 4 valence electrons which are finally placed in the high energy antibonding MOs (π*2px and π*2py), one in each (Hund’s rule) and then paired up in opposite spins (Pauli Exclusion Principle).  

This successfully completes the molecular orbital diagram of F2 as shown below.

Molecular orbital diagram (MO) of Fluorine (F2) and it's bond order

Is F2 diamagnetic or paramagnetic?

F2 is a diamagnetic molecule as there are no unpaired electrons in its molecular orbital diagram. Rather, even the electrons in the high-energy antibonding MOs (π*2px and π*2py) are paired up.

Diamagnetic substances possess no permanent dipole moment; therefore they get repelled by an external magnetic field.

Bond order of F2

The bond order formula is:

Bond order formula for F2

∴ Bond order = (Nb –Na)/2

  • Nb = Electrons present in the bonding MOs (Bonding electrons).

∴ Electrons in σ1s + σ2s + σ2pz + π2px + π2py = 2 + 2 + 2 + 2 + 2 = 10

  • Na= Electrons present in the anti-bonding MOs (Anti-bonding electrons).

∴ Electrons in σ*1s + σ*2s + π*2px + π*2py = 2 + 2 + 2 + 2 = 8

Bond order of F2 = (10 – 8)/2 = 2/2 = 1.  

A bond order of 1 implies that there is a single covalent bond (F-F) between two F-atoms in an F2 molecule.

MO diagrams and bond orders of F2+, F2, F22+ and F22-  

F2+ represents a cation of fluorine. It is a molecular ion formed by the loss of 1 valence electron from the fluorine molecule.

This valence electron is removed from the least stable, high-energy 2p atomic orbital of an F-atom. As a result, the Molecular orbital diagram of fluorine is transformed as shown below:

F2+ Molecular orbital diagram (MO) and Bond order

∴ Bond order of F2+ = (Nb –Na)/2 = (10 – 7)/2 = 1.5

Paramagnetic

Similarly, F22+ is formed by removing two electrons, one from a 2p AO of each F-atom. Therefore, the electrons present in both π*2px and π*2py MOs get unpaired to produce the F22+ Molecular orbital diagram.

∴ Bond order of F22+ = (Nb –Na)/2 = (10 – 6)/2 = 2

Paramagnetic

F22+ Molecular orbital diagram (MO) and Bond order

Contrarily, F2 is a negatively charged anion. 1 extra valence electron is gained by an F-atom. This extra electron singly fills σ*2pz in the Molecular orbital diagram of F2.

∴ Bond order of F2 = (Nb –Na)/2 = (10 – 9)/2 = 0.5

Paramagnetic

F2- Molecular orbital diagram (MO) and Bond order

Finally, F22- is formed when 2 extra valence electrons are gained, one by each parent F-atom. Consequently, these 2 electrons are accommodated as an electron pair in the highest energy antibonding MO i.e., σ*2pz, resulting in an F22- Molecular orbital diagram, completely filled with electrons.   

∴ Bond order of F22- = (Nb –Na)/2 = (10 –10)/2 = 0

Diamagnetic

F22- Molecular orbital diagram (MO) and Bond order

F22- is an exception. It is the only diamagnetic molecular ion out of all those discussed above.

However, a bond order of zero implies that the formation of F22- ion is extremely unlikely in real life. Rather, it is a hypothetical ion only.

The bond order also signifies the strength of a bond. Therefore, for the fluorine family, the bond strength increases as follows:

F22- < F2 < F2 < F2+ < F22+

However, bond order is inversely proportional to bond length. The greater the bond strength, the closer the bonded atoms are to each other.

Therefore, the bond lengths of the fluorine family decrease in the order:

F22- > F2 > F2 > F2+ > F22+

Also read:

FAQ

What is the molecular orbital diagram of F2?

The molecular orbital (MO) diagram of F2 is shown below.

MO diagram of F2

The MO electronic configuration of F2 is:

(σ1s2)(σ*1s2)(σ2s2)(σ*2s2) (σ 2pz2) (π2px2)(π2py2)(π*2px2) (π*2py2)

There are no unpaired electrons in the Molecular orbital diagram of F2; therefore, it is diamagnetic in nature.  The bond order of F2 is calculated as follows:

∴ Bond order of F2 = (Nb –Na)/2 = (10 – 8)/2 = 1.

How is the molecular orbital diagram of O2 different from that of F2?

O2 is a paramagnetic molecule, there are 2 unpaired electrons in the π*2px and π*2py MOs of oxygen.

Contrarily, both the π*2px and π*2py electrons get paired up due to a higher number of valence electrons in the individual atomic orbitals of F2.

Hence, F2 is a diamagnetic molecule. The MO diagrams of the two molecules are shown below. 

Molecular orbital diagram of F2 vs O2

What is the bond order of F2?

The bond order of F2 is 1.

∴ Bond order = (Nb – Na)/2

As per the MO diagram of F2, Nb = 10 and Na = 8

∴ Bond order = (10 – 8)/2

∴ Bond order = 2/2  = 1

How many electrons are in the bonding and antibonding molecular orbitals of F2?

There are a total of 10 electrons in the bonding molecular orbitals of F2.

There are 8 electrons in the antibonding molecular orbitals of F2.

How many paired and unpaired electrons are there in the MO diagram of F2?

There are no unpaired electrons in the Molecular orbital diagram of F2. Rather, all 18 electrons are paired in sets of 2. Hence, there are 9 electron pairs in the F2 molecular orbital diagram.

What is the molecular orbital diagram of F2

F2 is a negatively charged molecular ion. One out of the two identical F-atoms gains an extra valence electron to produce the F2 ion.

This extra valence electron is accommodated in the highest energy σ*2pz MO of fluorine.

What is the bond order of F2+

F2+ is a cation formed by the loss of 1 valence electron from one of the two F-atoms in the F2 molecule. Therefore, its MO electronic configuration is:

(σ1s2)(σ*1s2)(σ2s2)(σ*2s2) (σ 2pz2) (π2px2)(π2py2)(π*2px2) (π*2py1)

Nb = 10 and Na = 7 give a bond order of:

∴ Bond order = (10 – 7)/2 = 1.5

As per the molecular orbital theory, is F22+ paramagnetic or diamagnetic?  

F22+ is a paramagnetic substance as there are two unpaired electrons in its MO diagram. The loss of 2 electrons from F2 means both the π*2px and π*2py electrons get unpaired in the molecular orbital diagram. 

Which of the three molecular ions is the most likely to form?

F2+, F22+ or F2

F22+ is the most likely to form as it possesses the highest bond order out of the three molecular ions mentioned above.

  • Bond order of F2+ = 1.5
  • Bond order of F22+ =2
  • Bond order of F2 = 0.5

A higher bond order denotes a greater bond strength thus a higher probability of bond formation in real life.

Summary

  • Fluorine (F2) is a homonuclear diatomic molecule. Two identical F-atoms combine to form F2.
  • As per MOT, 10 atomic orbitals of individual fluorine atoms combine to form 10 molecular orbitals including 5 bonding and 5 antibonding MOs.
  • The MO electronic configuration of F2 is (σ1s2)(σ*1s2)(σ2s2)(σ*2s2) (σ 2pz2) (π2px2)(π2py2)(π*2px2) (π*2py2).
  • The absence of any unpaired electrons in the Molecular orbital diagram of F2 denotes it is a diamagnetic substance.
  • The bond order of F2 is 1 which means there is a single covalent bond between two F-atoms in the F2 molecule.
  • F2+, F2, F22+, and F22- are molecular ions formed by the loss or gain of electrons in the valence shell atomic orbitals of individual F-atoms.
  • The bond order follows the ascending pattern: F22- < F2 < F2 < F2+ < F22+ i.e., 0, 0.5, 1, 1.5, and 2 respectively.
  • F2+, F2 and F22+ are all paramagnetic while F22- is diamagnetic in nature.
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Vishal Goyal author of topblogtenz.com

Vishal Goyal is the founder of Topblogtenz, a comprehensive resource for students seeking guidance and support in their chemistry studies. He holds a degree in B.Tech (Chemical Engineering) and has four years of experience as a chemistry tutor. The team at Topblogtenz includes experts like experienced researchers, professors, and educators, with the goal of making complex subjects like chemistry accessible and understandable for all. A passion for sharing knowledge and a love for chemistry and science drives the team behind the website. Let's connect through LinkedIn: https://www.linkedin.com/in/vishal-goyal-2926a122b/

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