Question

Which statement of the following is false for isoelectronic species? (1) They have same outer electronic configuration. (2) Their bond orders are same. (3) Their outer electronic configuration is different. (4) Their bond energies are nearly same.

Short answer

Statement (3) is false for isoelectronic species.

Step-by-step solution

Define Isoelectronic Species

Isoelectronic species are atoms, molecules, or ions that have the same number of electrons.

Evaluate Option (1)

Isoelectronic species have the same number of electrons, which means they have the same outer electronic configuration. Therefore, statement (1) is true.

Evaluate Option (2)

Bond order depends on the number of electrons in bonding and antibonding molecular orbitals. Isoelectronic species often have the same bond order if they have similar electron distribution. Thus, statement (2) can be considered true.

Evaluate Option (3)

Since isoelectronic species have the same number of electrons, their outer electronic configuration should be the same, not different. Therefore, statement (3) is false.

Evaluate Option (4)

Bond energy is influenced by bond order and other factors, which can make bond energy fairly similar in isoelectronic species. Thus, statement (4) can be considered true.

Conclusion

Based on the evaluation of the statements, statement (3) is the false one for isoelectronic species.

Key concepts

Electronic Configuration

Electronic configuration refers to the arrangement of electrons in an atom, molecule, or ion. The configuration is important because it determines how the entity interacts with other chemicals via bonding.
For isoelectronic species, which are atoms or ions having the same number of electrons, the electronic configuration of the outermost electrons will be the same. This similarity in electron configuration leads to many shared chemical properties.

For example:

• Neon (Ne): 1s² 2s² 2p⁶
• Sodium Ion (Na⁺): 1s² 2s² 2p⁶
• Fluoride Ion (F⁻): 1s² 2s² 2p⁶

Although these species differ in the number of protons and neutrons, they share the same number of electrons, making them isoelectronic with each other.
This similarity results in them having the same outer electronic configuration, thus confirming statement (1) as true but making statement (3) false in the given exercise.

Bond Order

Bond order essentially measures the strength and stability of a bond. It is calculated by subtracting the number of antibonding electrons from the number of bonding electrons and then dividing by two: \[ \text{Bond Order} = \frac{(\text{Number of bonding electrons} - \text{Number of antibonding electrons})}{2} \]
For isoelectronic species, the similar number of electrons generally means similar electron distributions in bonding and antibonding molecular orbitals.
This results in a similar bond order. For instance, consider the following species:

• C₃: Bond Order of 2.0
• NN: Bond Order of 2.0

Here, both species have similar bonding characteristics due to their isoelectronic nature.

Therefore, option (2) holds as true in the context of isoelectronic species.

Bond Energy

Bond energy is the amount of energy required to break a bond between two atoms. It's closely related to bond order. Generally, the higher the bond order, the stronger the bond and the higher the bond energy.

Isoelectronic species, having the same number of electrons, often exhibit very similar bond energies because their bonds involve similar electronic arrangements.
Let's compare:

• CO: Bond Energy of 1076 kJ/mol
• CN⁻: Bond Energy of 1012 kJ/mol

Here, though nearly the same, the slight difference is influenced by factors like atomic size and electronegativity. Nonetheless, the bond energies of isoelectronic species are still closely related.
Thus, statement (4) indicating that bond energies are nearly the same is also true for isoelectronic species in the given exercise.