Q43E - Chemistry (OpenStax)

Question

Compare the atomic and molecular orbital diagrams to identify the member of each of the following pairs that has the highest first ionization energy (the most tightly bound electron) in the gas phase:

(a) \({\rm{H}}\) and \({{\rm{H}}_{\rm{2}}}\)

(b) \({\rm{N}}\)and \({{\rm{N}}_{\rm{2}}}\) 

(c) \({\rm{O}}\)and \({{\rm{O}}_{\rm{2}}}\)

(d) \({\rm{C}}\)and \({{\rm{C}}_{\rm{2}}}\)

(e) \({\rm{B}}\)and \({{\rm{B}}_{\rm{2}}}\)

Step-by-Step Solution

Answer

(a) \({{\rm{H}}_{\rm{2}}}\) has the highest first ionization energy because we need remove an electron from bonding molecular orbital.

(b) \({{\rm{N}}_2}\) has the highest first ionization energy because we need remove an electron from bonding molecular orbital.

(c) O has the highest first ionization energy because we need to remove an electron from antibonding molecular orbital in \({{\rm{O}}_2}\).

(d) \({C_2}\)has the highest first ionization energy because we need to remove an electron from bonding molecular orbital.

(e) \({{\rm{B}}_2}\) has the highest first ionization energy because we need to remove an electron from bonding molecular orbital.

Step 1: Definition of bonding molecular orbital

Bonding orbitals are used in molecular orbital theory (MO) to describe the attractive interactions between the atomic orbitals of two or more atoms in a molecule.

Step 2: Comparing H and H 2

Bonding molecular orbitals are more stable  atomic orbitals, and antibonding molecular orbitals are less stable atomic orbitals.

(a)

\({{\rm{H}}_{\rm{2}}}\)has the highest first ionization energy because we need remove an electron from bonding molecular orbital.

Step 3: Comparing N and N 2

b)

\({{\rm{N}}_2}\) has the highest first ionization energy because we need remove an electron from bonding molecular orbital

Step 4: Comparing O and O 2

c)

O has the highest first ionization energy because we need to remove an electron from antibonding molecular orbital in \({{\rm{O}}_2}\).

Step 5: Comparing C and C 2

d)

\({C_2}\) has the highest first ionization energy because we need to remove an electron from bonding molecular orbital

Step 6: Comparing B and B 2

e)

\({{\rm{B}}_2}\) has the highest first ionization energy because we need to remove an electron from bonding molecular orbital