Change to the methionine amino acid. How many valence electrons are in methionine? 14b. Evaluating the methionine structure O=C-O C-S-C (S is yellow) H-N-C (H bound to N, N is blue) (1pts) 54 Table view List view Measured bond angle VSEPR Idealized bond angle 122.0 120.0 98.6 108.2 104.5 107.0 14c. Are these results for the methionine structure consistent with what you observed in Avogadro (within a few degrees)? Explain briefly. Normal BIIIU XX No ? Saved T Saved
The Correct Answer and Explanation is:
14a. Valence Electrons in Methionine
Methionine (C₅H₁₁NO₂S) is an amino acid. To determine the number of valence electrons in methionine, we need to count the valence electrons of each atom in the molecule.
- Carbon (C): Each carbon atom has 4 valence electrons, and there are 5 carbon atoms in methionine. So, 5×4=205 \times 4 = 205×4=20 valence electrons from carbon.
- Hydrogen (H): Each hydrogen atom has 1 valence electron, and there are 11 hydrogen atoms. So, 11×1=1111 \times 1 = 1111×1=11 valence electrons from hydrogen.
- Nitrogen (N): Nitrogen has 5 valence electrons, and there is 1 nitrogen atom. So, 1×5=51 \times 5 = 51×5=5 valence electrons from nitrogen.
- Oxygen (O): Oxygen has 6 valence electrons, and there are 2 oxygen atoms in methionine. So, 2×6=122 \times 6 = 122×6=12 valence electrons from oxygen.
- Sulfur (S): Sulfur has 6 valence electrons, and there is 1 sulfur atom. So, 1×6=61 \times 6 = 61×6=6 valence electrons from sulfur.
Now, adding them all together:
20+11+5+12+6=5420 + 11 + 5 + 12 + 6 = 5420+11+5+12+6=54 valence electrons in methionine.
14b. Evaluating the Methionine Structure
You provided a simplified structure of methionine:
- The molecule has a C-S-C backbone with a sulfur atom (yellow) bound to two carbon atoms.
- The nitrogen atom is bonded to a hydrogen atom (H-N), and this nitrogen is part of the amino group.
- The structure includes a C=O double bond, indicating a carboxyl group (COOH).
In terms of VSEPR theory:
- The C=O bond is expected to be linear because it involves a double bond to oxygen.
- The C-S-C bond angle could be close to 120° because the structure resembles a planar geometry around the central carbon atoms (sp² hybridization).
- The N-H bond should show a typical bond angle around 107° because nitrogen is sp³ hybridized, leading to a trigonal pyramidal geometry.
14c. Are the Results for the Methionine Structure Consistent with Avogadro?
Using Avogadro or other molecular modeling tools, the results from VSEPR theory should largely align with observed bond angles. For methionine, the bond angles you provided (122°, 98.6°, 104.5°) suggest that the structure is close to idealized angles for sp³, sp², or hybridized bonds. However, slight deviations are expected due to the real-world interactions of atoms in three dimensions.
- 122.0° vs. 120.0°: A small difference of around 2 degrees is acceptable. The bond angle in the C-S-C might slightly deviate due to the non-ideal nature of actual bond geometry.
- 98.6° and 104.5°: These are somewhat lower than the typical 109.5° for sp³ hybridized atoms (such as nitrogen in the amino group), suggesting some strain in the molecule due to the involvement of heteroatoms like sulfur and oxygen.
In summary, the results are generally consistent with Avogadro’s simulation, with minor differences likely due to real atomic interactions. The slight bond angle differences can be attributed to factors such as lone pairs and atomic radii, which deviate slightly from idealized VSEPR theory predictions.
