Here are the corrections and explanations for the chemistry problems shown in your worksheet. I have checked the calculations for valence electrons, shapes, and angles to ensure they are accurate.
5. Nitrite Ion ($NO_2^-$)
1. Total Valence Electrons:
*
Nitrogen (N): Group 15 $\rightarrow$ 5 valence electrons.
*
Oxygen (O): Group 16 $\rightarrow$ 6 valence electrons $\times$ 2 atoms = 12.
*
Charge (-1): Add 1 electron.
*
Total: $5 + 12 + 1 = \mathbf{18}$
electrons.
* *Your calculation ($5+12-(-1)=18$) is correct.*
2. Lewis Structure:
* You correctly drew the two resonance structures: one with a double bond on the left and one on the right.
*
Check: Each structure has 18 electrons total. The central Nitrogen has a formal charge of +1, the single-bonded Oxygen has -1, and the double-bonded Oxygen is 0. Net charge = -1. This is correct.
3. Molecular Shape & Angles:
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Electron Domains: The central Nitrogen has 3 domains (one double bond, one single bond, and one lone pair).
*
Geometry: Trigonal Planar electron geometry.
*
Molecular Shape: Because of the lone pair, the shape is
Bent (or V-shaped).
*
Bond Angle: Ideal trigonal planar is $120^\circ$. The lone pair pushes the bonds closer together. So, the angle is
$< 120^\circ$ (approx $115^\circ$).
* *Your answers are correct.*
4. Polarity & Symmetry:
*
Polar Bonds? Yes. N and O have different electronegativities.
*
Symmetry? Asymmetric. The molecule is bent and has a net dipole moment (it is polar). It does not cancel out.
* *Your answers are correct.*
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6. Hydronium Ion ($H_3O^+$)
1. Total Valence Electrons:
*
Hydrogen (H): 1 valence electron $\times$ 3 atoms = 3.
*
Oxygen (O): 6 valence electrons.
*
Charge (+1): Subtract 1 electron.
*
Total: $3 + 6 - 1 = \mathbf{8}$
electrons.
* *Your calculation ($1\times3+6-1=8$) is correct.*
2. Lewis Structure:
* Oxygen in the center bonded to 3 Hydrogens.
* Oxygen needs 8 electrons total. It uses 6 for bonds (3 pairs). It keeps the remaining 2 as a
lone pair.
* *Your drawing shows the correct connections and the lone pair on top.*
3. Molecular Shape & Angles:
*
Electron Domains: 4 domains (3 bonding pairs + 1 lone pair).
*
Geometry: Tetrahedral electron geometry.
*
Molecular Shape: With one lone pair, the shape is
Trigonal Pyramidal.
*
Bond Angle: Ideal tetrahedral is $109.5^\circ$. The lone pair pushes the H atoms down slightly. So, the angle is
$< 109.5^\circ$ (approx $107^\circ$).
* *Your answers are correct.*
4. Polarity & Symmetry:
*
Polar Bonds? Yes. O-H bonds are polar.
*
Symmetry? Asymmetric. The lone pair makes the charge distribution uneven. The dipoles do not cancel out.
* *Your answers are correct.*
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Summary of Corrections/Confirmations
Your work for items 5 and 6 is excellent. Here is a quick summary of the key facts for your records:
Item 5: $NO_2^-$
*
Valence Electrons: 18
*
Shape: Bent
*
Angle: $< 120^\circ$
*
Symmetry: Asymmetric (Polar)
Item 6: $H_3O^+$
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Valence Electrons: 8
*
Shape: Trigonal Pyramidal
*
Angle: $< 109.5^\circ$
*
Symmetry: Asymmetric (Polar)
Parent Tip: Review the logic above to help your child master the concept of molecular shape worksheet.
