Question

question 5: remember, on the actual exam, you cant search google images for this information! you must rely on what was taught to you in h. chem for drawing lewis dot structures.
a) draw the 2 resonance structures for ozone, o₃
b) draw the 2 resonance structures for cooh⁻
c) draw the 3 resonance structures for ncs⁻. circle the structure is the most viable/valid based on your assessment of their formal charges.
question 6 matching: label the 6 diagrams with one of the following choices: ionic compound (a.k.a. crystal lattice), brittleness, interstitial alloy, substitutional alloy, malleability, conductivity. will all be used at least once.
electron sea

Explanation:

Step1: Draw resonance structures for ozone ($O_3$)

Ozone has a central oxygen atom double - bonded to one oxygen and single - bonded to another. The resonance structures are:
$O = O - O$ and $O - O = O$. The formal charges are calculated as follows: For the central O in $O = O - O$, valence electrons of O is 6, non - bonding electrons is 2, and bonding electrons is 6. Formal charge = $6-(2 + \frac{6}{2})=1$. For the double - bonded O, formal charge = $6-(4+\frac{4}{2}) = 0$. For the single - bonded O, formal charge = $6-(6+\frac{2}{2})=-1$. The two resonance structures distribute the formal charges.

Step2: Draw resonance structures for $COOH^-$

The $COOH^-$ has a carbon atom double - bonded to one oxygen and single - bonded to another oxygen with a negative charge. The resonance structures are: $O = C - O^-$ and $O^- - C = O$. For the carbonyl O in $O = C - O^-$, formal charge = $6-(4+\frac{4}{2}) = 0$. For the single - bonded O with negative charge, formal charge = $6-(6+\frac{2}{2})=-1$.

Step3: Draw resonance structures for $NCS^-$

The possible resonance structures for $NCS^-$ are: $N≡C - S^-$, $^-N = C = S$, and $N - C≡S^-$. Calculate formal charges: In $N≡C - S^-$, for N, formal charge = $5-(2+\frac{6}{2}) = 0$, for C, formal charge = $4-(0+\frac{8}{2}) = 0$, for S with negative charge, formal charge = $6-(6+\frac{2}{2})=-1$. In $^-N = C = S$, for N with negative charge, formal charge = $5-(6+\frac{2}{2})=-1$, for C, formal charge = $4-(0+\frac{8}{2}) = 0$, for S, formal charge = $6-(4+\frac{4}{2}) = 0$. In $N - C≡S^-$, for N, formal charge = $5-(4+\frac{4}{2})=-1$, for C, formal charge = $4-(0+\frac{8}{2}) = 0$, for S with negative charge, formal charge = $6-(6+\frac{2}{2})=-1$. The most valid structure is usually the one with the least separation of formal charges and negative charge on the more electronegative atom. For $NCS^-$, $^-N = C = S$ is a more valid structure as S is more electronegative than N and can better accommodate the negative charge in the resonance hybrid.

Step4: Match diagrams for crystal lattice and alloys

• Ionic compound: Diagram (d) represents an ionic compound with alternating positive and negative ions.
• Interstitial alloy: Diagram (b) shows an interstitial alloy where smaller atoms fit into the holes of the lattice of larger atoms.
• Substitutional alloy: Diagram (e) shows a substitutional alloy where atoms of similar size replace each other in the lattice.
• Crystal lattice (metallic - electron sea model): Diagram (a) represents a metallic crystal lattice with a sea of delocalized electrons surrounding positive metal ions.
• Malleability is associated with metallic lattices (a) as the delocalized electrons allow the metal ions to slide past each other.
• Brittleness is associated with ionic compounds (d) as the strong electrostatic forces between ions can be disrupted by dislocation of ions.
• Conductivity is associated with metallic lattices (a) due to the presence of delocalized electrons.

Answer:

a) Resonance structures for ozone ($O_3$):
$O = O - O$ and $O - O = O$
b) Resonance structures for $COOH^-$:
$O = C - O^-$ and $O^- - C = O$
c) Resonance structures for $NCS^-$: $N≡C - S^-$, $^-N = C = S$, $N - C≡S^-$; most valid is $^-N = C = S$
d) Ionic compound: Diagram (d)
e) Interstitial alloy: Diagram (b)
f) Substitutional alloy: Diagram (e)
g) Crystal lattice (metallic - electron sea model): Diagram (a)
h) Malleability: Diagram (a)
i) Brittleness: Diagram (d)
j) Conductivity: Diagram (a)