# How to draw Molecular Orbital Diagram of Li2 , Li 2+ , Li2 -|Chemistry

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Lithium belongs to group 1 ( alkali metals), period 2 s-block element of the periodic table.

Lithium is represented by the symbol “Li”.

The atomic number of Lithium (Li ) is 3 and the mass number is 6.941.

## Li Electronic Configuration:

The distribution of electrons in lithium electronic shells are as follow:

K shell = 2 electrons

L shell = 1 electron

so the electron configuration is :

The electronic configuration of the Li atom is 1s2 2s1.

How do draw the Molecular Orbital Diagram of Lithium molecule (Li2)?

According to the molecular orbital theory, the molecular orbital diagram of the lithium molecule is shown below:

The 2 electrons are present in σ 2s orbitals.

The antibonding molecular orbital σ*2 s is empty.

Thus

Bond order = Number of electrons in BMO – Number of electrons in ABMO

2

Bond order = 2-0

2

Bond order = 1

Bond order 1 shows that there is a single covalent bond between the lithium atoms in the Li2 molecule.

### How to draw the molecular orbital diagram of Li2, Li2 +, Li2 –?

Incase of Li2 +, the 1 electrons are present in σ 2s orbitals.

The antibonding molecular orbital σ*2 s is empty.

Thus

Bond order = Number of electrons in BMO – Number of electrons in ABMO

2

Bond order = 1-0

2

Bond order = 0.5

Similarly,

In the case of Li2 -, the 2 electrons are present in σ 2s orbitals.

The antibonding molecular orbital σ*2 s contains 1 electron.

Thus

Bond order = Number of electrons in BMO – Number of electrons in ABMO

2

Bond order = 2-1

2

Bond order = 0.5

## Arrange the following species in increasing order of stability:Li2, Li2 +, Li2 –

Since the bond order of Li2 is higher than Li2 + and Li2 -. Therefore, Li2 has stronger single covalent bonding. Thus lithium molecule (Li2) is more stable.

## Li2 + is more stable as compared to Li2 – :

Li2 + and Li2 ions have the same bond order ( 0.5).

But Li2 has more electrons in higher energy antibonding molecular orbital as compared to Li2 +.

Thus Li2 + is more stable than Li2.

so the increasing order of stability is:

Li2 > Li2 + > Li2

Simplest Trick to Calculate Bond Order :

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