8.4 Molecular orbital theory  (Page 10/26)

Sketch the distribution of electron density in the bonding and antibonding molecular orbitals formed from two s orbitals and from two p orbitals.

How are the following similar, and how do they differ?

(a) σ molecular orbitals and π molecular orbitals

(b) ψ for an atomic orbital and ψ for a molecular orbital

(c) bonding orbitals and antibonding orbitals

If molecular orbitals are created by combining five atomic orbitals from atom A and five atomic orbitals from atom B combine, how many molecular orbitals will result?

Can a molecule with an odd number of electrons ever be diamagnetic? Explain why or why not.

Can a molecule with an even number of electrons ever be paramagnetic? Explain why or why not.

Why are bonding molecular orbitals lower in energy than the parent atomic orbitals?

Calculate the bond order for an ion with this configuration:

Explain why an electron in the bonding molecular orbital in the H ₂ molecule has a lower energy than an electron in the 1 s atomic orbital of either of the separated hydrogen atoms.

Predict the valence electron molecular orbital configurations for the following, and state whether they will be stable or unstable ions.

(a) ${\text{Na}}_2{}^{\text{2+}}$

(b) ${\text{Mg}}_2{}^{\text{2+}}$

(c) ${\text{Al}}_2{}^{\text{2+}}$

(d) ${\text{Si}}_2{}^{\text{2+}}$

(e) ${\text{P}}_2{}^{\text{2+}}$

(f) ${\text{S}}_2{}^{\text{2+}}$

(g) ${\text{F}}_2{}^{\text{2+}}$

(h) ${\text{Ar}}_2{}^{\text{2+}}$

Determine the bond order of each member of the following groups, and determine which member of each group is predicted by the molecular orbital model to have the strongest bond.

(a) H ₂ , ${\text{H}}_2{}^{\text{+}},$ ${\text{H}}_2{}^{\text{−}}$

(b) O ₂ , ${\text{O}}_2{}^{\text{2+}},$ ${\text{O}}_2{}^{\text{2−}}$

(c) Li ₂ , ${\text{Be}}_2{}^{\text{+}},$ Be ₂

(d) F ₂ , ${\text{F}}_2{}^{\text{+}},$ ${\text{F}}_2{}^{\text{−}}$

(e) N ₂ , ${\text{N}}_2{}^{\text{+}},$ ${\text{N}}_2{}^{\text{−}}$

For the first ionization energy for an N ₂ molecule, what molecular orbital is the electron removed from?

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) H and H ₂

(b) N and N ₂

(c) O and O ₂

(d) C and C ₂

(e) B and B ₂

Which of the period 2 homonuclear diatomic molecules are predicted to be paramagnetic?

A friend tells you that the 2 s orbital for fluorine starts off at a much lower energy than the 2 s orbital for lithium, so the resulting σ _{2 s} molecular orbital in F ₂ is more stable than in Li ₂ . Do you agree?

True or false: Boron contains 2 s ² 2 p ¹ valence electrons, so only one p orbital is needed to form molecular orbitals.

What charge would be needed on F ₂ to generate an ion with a bond order of 2?

Predict whether the MO diagram for S ₂ would show s-p mixing or not.

Explain why ${\text{N}}_2{}^{\text{2+}}$ is diamagnetic, while ${\text{O}}_2{}^{\text{4+}},$ which has the same number of valence electrons, is paramagnetic.

Using the MO diagrams, predict the bond order for the stronger bond in each pair:

(a) B ₂ or ${\text{B}}_2{}^{\text{+}}$

(b) F ₂ or ${\text{F}}_2{}^{\text{+}}$

(c) O ₂ or ${\text{O}}_2{}^{\text{2+}}$

(d) ${\text{C}}_2{}^{\text{+}}$ or ${\text{C}}_2{}^{\text{−}}$