QQuestionChemistry
QuestionChemistry
Draw a Lewis structure for NO, indicating whether NO could be expected to be a stable molecule from the Lewis structure. Draw a molecular orbital diagram for NO. Does MO theory predict NO to be stable (include bond order in your answer)? Comment on the differences between predictions from the Lewis structure and that from MO theory.
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Answer
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Step 1:: Draw the Lewis structure for NO.
Nitrogen (N) has 5 valence electrons and Oxygen (O) has 6 valence electrons. Since there is one N atom and one O atom in the NO molecule, there will be a total of 11 valence electrons. The Lewis structure for NO is: \mathrm{O:}---\mathrm{N:}
Step 2:: Evaluate the stability of the NO molecule based on the Lewis structure.
The Lewis structure shows that Nitrogen has a formal charge of + 1 and Oxygen has a formal charge of - 1. This indicates that the Lewis structure does not satisfy the octet rule for both atoms. In general, a molecule is considered stable if it follows the octet rule and has minimal formal charges.
Step 3:: Draw the molecular orbital (MO) diagram for NO.
The atomic orbitals involved in forming the NO molecule are the 2s and 2p orbitals of Nitrogen and Oxygen. The molecular orbitals are formed by the linear combination of atomic orbitals (LCAO). The order of energy for the MOs is as follows (from lowest to highest energy):
Step 4:
N(2s) and O(2s) -> bonding σ (sigma) orbital
Step 5:
N(2s) and O(2s) -> antibonding σ* (sigma star) orbital
Step 6:
N(2p) and O(2p) -> bonding π (pi) orbitals (2)
Step 7:
N(2p) and O(2p) -> antibonding π* (pi star) orbitals (2)
Step 8:: Evaluate the stability of the NO molecule based on the MO diagram.
The bonding σ and π orbitals are occupied by one electron each, while the antibonding σ* and π* orbitals are unoccupied. The bond order of NO can be calculated by subtracting the number of electrons in antibonding orbitals from the number of electrons in bonding orbitals, and then dividing by 2: Bond order = (number of electrons in bonding orbitals - number of electrons in antibonding orbitals) / 2 Bond order = (2 - 0) / 2 = 1
Step 9:: Compare the predictions from the Lewis structure and MO theory.
The Lewis structure suggests that NO is not a stable molecule due to the presence of formal charges. However, the MO diagram shows that NO has a bond order of 1, which indicates a stable molecule. In reality, NO is a stable molecule with a bond order of 2.5. This discrepancy between the Lewis structure and MO theory can be attributed to the fact that the Lewis structure does not account for the delocalization of electrons, which is captured in the MO diagram. The MO theory provides a more accurate description of the electronic structure of NO, and it is more suitable for predicting the stability of molecules with multiple bonds or unpaired electrons.
Final Answer
The Lewis structure for NO indicates that it could not be expected to be a stable molecule due to the presence of formal charges. However, the MO diagram shows that NO has a bond order of 1, suggesting that it is a stable molecule. This discrepancy highlights the limitations of the Lewis structure and the advantages of the MO theory in predicting the stability of molecules.
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