Question

Part A

Use the drawing of the MO energy diagram to predict the bond order of Li2+.

Express the bond order as an integer or fraction.

Part B

Use the drawing of the MO energy diagram to predict the bond order of Li2?.

Express the bond order as an integer or fraction.

Part C

Which molecules are predicted to exist in the gas phase?

Check all that apply

Check all that apply

	Li2?
	Li2+

Answer 1

Concepts and reason

The concept used to solve this problem is calculated bond order ofand by using MO diagram.

Fundamentals

The bond order in a molecule is one-half the difference between the number of electron in bonding molecular orbitals and the number in anti-bonding molecular orbitals.

Importance of bond order is as follows:

1.Stability of molecules or ions:

If the bond order is positive the molecule or ions will be stable, but if the value of bond order is zero or negative the molecule or ion will be un-stable.

2.Bond dissociation energy:

The relation between Bond dissociation energy and bond order is direct proportional therefore when bond order is high then the bond dissociation energy greater will be.

3.Bond length:

The relation between Bond length and bond order is inversely proportional

Therefore greater the bond order, smaller will be the bond length.

4.Number of bonds:

The value of bond order is equal to the number of covalent bonds in the molecules. For example if the value of bond order is 2, thus there are two covalent bonds.

When all electrons are paired then the species is diamagnetic while Para-magnetism requires unpaired electrons.

Part a

The general molecular orbital is formed as follows:

The sigma (σ) bonding molecular orbitals, the electron probability of both molecular orbitals are centered along the line passing through the two nuclei.

The sigma (σ) bonding molecular orbital

When the parallel p orbital are combined with the positive and negative phases matched, constructive interference occurs, giving a bonding π orbital, electron probability lies above and below the line between the nuclei.

Bonding π orbital

The sigma (σ^*) anti-bonding molecular orbitals, the anti-bonding MO has greater electron probability on either side of nuclei.

The sigma (σ^*) anti-bonding molecular orbitals

When the parallel p orbital have opposite phase the π^* anti-bonding MO are formed.

The π^* anti-bonding MO orbital

The atomic number of lithium is 3, thus there are 6 electrons are present in lithium molecular while 5 electron are present in ion.

The following Molecular orbital s are occupied in and:

Calculate the bond order as follows:

Part b

The following Molecular orbital s are occupied in and :

Calculate the bond order as follows:

Part c

The bond order of and ions are 0.5 which is a positive value.

Ans: Part a

Thus, the bond order in is 0.5.

Part b

Thus, the bond order in is 0.5.

Part c

Thus, both and ion exist in gas phase.