Question

(a) The nitric oxide molecule, NO, readily loses one electron to form the \(\mathrm{NO}^{+}\) ion. Which of the following is the best explanation of why this happens: (i) Oxygen is more electronegative than nitrogen, (ii) The highest energy electron in NO lies in a \(\pi_{2 p}^{*}\) molecular orbital, or (iii) The \(\pi_{2 p}^{*}\) MO in NO is completely filled. (b) Predict the order of the \(\mathrm{N}-\mathrm{O}\) bond strengths in \(\mathrm{NO}, \mathrm{NO}^{+},\) and \(\mathrm{NO}^{-},\) and describe the magnetic properties of each.(c) With what neutral homonuclear diatomic molecules are the \(\mathrm{NO}^{+}\) and \(\mathrm{NO}^{-}\) ions isoelectronic (same number of electrons)?

Short answer

Answer: (a) The best explanation for why the nitric oxide molecule (NO) readily loses one electron to form the NO+ ion is (ii) The highest energy electron in NO lies in a \(\pi_{2p}^*\) molecular orbital. (b) The order of the N-O bond strengths in NO, NO+, and NO- is: NO- < NO < NO+. NO and NO- are paramagnetic, and NO+ is diamagnetic. (c) The neutral homonuclear diatomic molecules that are isoelectronic with NO+ and NO- ions are N2 (for NO+) and O2 (for NO-).

Step-by-step solution

Identify the electron configuration of NO

Determine the number of valence electrons for both nitrogen (N) and oxygen (O). The Nitrogen atom has 5 valence electrons and Oxygen has 6 valence electrons. Therefore, the NO molecule has a total of 5 + 6 = 11 valence electrons.

Identify the highest energy electron in NO

The electron configuration of the nitric oxide (NO) molecule is: \( \sigma_{1s}^2\sigma_{2s}^2\sigma_{2p}^4\pi_{2p}^4\sigma_{2p}^*\pi_{2p}^*\). The highest energy electron lies in a \(\pi_{2p}^*\) molecular orbital.

Verify the explanations for NO losing an electron

(i) Oxygen is more electronegative than nitrogen: This statement is true, but it does not directly explain why NO loses an electron to form NO+. (ii) The highest energy electron in NO lies in a \(\pi_{2p}^*\) molecular orbital: This statement is true and explains that the electron can be easily removed from NO. (iii) The \(\pi_{2p}^*\) MO in NO is completely filled: This statement is false, as the highest occupied molecular orbital (HOMO) of NO is not completely filled. Answer: (ii) The highest energy electron in NO lies in a \(\pi_{2p}^*\) molecular orbital. #b - Predicting bond strength and magnetic properties of NO, NO+, and NO-#

Calculate bond order and magnetic properties for NO, NO+, and NO-

For NO (11 valence electrons): Bond order = (8-3) / 2 = 2.5, Magnetic property: Paramagnetic For NO+ (10 valence electrons): Bond order = (8-2) / 2 = 3, Magnetic property: Diamagnetic For NO- (12 valence electrons): Bond order = (8-4) / 2 = 2, Magnetic property: Paramagnetic

Predict bond strength and magnetic properties based on bond order calculations

The N-O bond strengths increase as the bond order increases. Therefore, the bond strength order in NO, NO+, and NO- is: NO- < NO < NO+. NO and NO- are paramagnetic, and NO+ is diamagnetic. #c - Neutral homonuclear diatomic molecules isoelectronic with NO+ and NO- ions#

Count the number of valence electrons in NO+ and NO- ions

NO+ ion has 10 valence electrons (one less than the NO molecule) and NO- ion has 12 valence electrons (one more than the NO molecule).

Identify neutral homonuclear diatomic molecules with the same number of valence electrons

The neutral homonuclear diatomic molecule isoelectronic with the NO+ ion (10 valence electrons) is N2, as it has 5 + 5 = 10 valence electrons. The neutral homonuclear diatomic molecule isoelectronic with the NO- ion (12 valence electrons) is O2, as it has 6 + 6 = 12 valence electrons.

Key concepts

Bond Order

Bond order is a crucial concept in molecular orbital theory, and it helps us understand the strength and stability of bonds in molecules. The bond order is calculated as half the difference between the number of bonding electrons and the number of antibonding electrons.

• A higher bond order indicates a stronger and more stable bond.
• A bond order of one corresponds to a single bond, two to a double bond, and so on.

For nitric oxide (NO), NO⁺, and NO^-, the bond orders can be calculated using their respective electron configurations.
In NO (11 valence electrons), the bond order is 2.5, indicating a bond stronger than a double bond but weaker than a triple bond.
For NO⁺ (10 valence electrons), the bond order is 3, suggesting a triple bond, which implies a very strong bond.
Conversely, NO^- (12 valence electrons) has a bond order of 2, equating to a double bond and indicating it is the weakest among the three. These calculations reveal that the order of bond strength is: NO^- < NO < NO⁺.

Paramagnetic vs Diamagnetic

In molecular orbital theory, understanding whether a molecule or ion is paramagnetic or diamagnetic involves examining its unpaired electrons.

• Paramagnetic species have at least one unpaired electron and are attracted to magnetic fields.
• Diamagnetic species have all electrons paired and are slightly repelled by magnetic fields.

The nitric oxide series gives a clear illustration:
- **NO** contains an unpaired electron due to its electron configuration (\( \pi_{2p}^*\)), rendering it paramagnetic.
- **NO⁺** loses one electron from that configuration, resulting in all electrons being paired, making the ion diamagnetic.
- **NO^-** gains an extra electron back in the antibonding orbital (\( \pi_{2p}^*\)), so it also remains paramagnetic due to that unpaired electron.Identifying paramagnetism or diamagnetism is simple once you determine if unpaired electrons exist.

Isoelectronic Species

Isoelectronic species are molecules or ions that have the same number of electrons and often have similar properties. This concept is valuable because it helps predict the behavior and characteristics of substances.

• Molecules or ions with the same number of electrons can share similar bonding and structure.
• Being isoelectronic doesn't always equate to identical properties, but there can be notable similarities.

For the NO⁺ and NO^- ions:
- **NO⁺** is isoelectronic with nitrogen gas (N₂). Both have 10 electrons in total. This is often why N₂ and NO⁺ are considered similar in terms of stability owing to their full complement of electrons.
- **NO^-** is isoelectronic with oxygen gas (O₂), with 12 electrons. This comparison provides insight into their possible reactivity and magnetic properties. Understanding isoelectronic species is helpful to predict and compare the properties of different molecules or ions efficiently.