a) Carbonic Acid (H₂CO₃)
To draw the Lewis structure for carbonic acid, we start by identifying the total number of valence electrons. Carbon (C) has 4 valence electrons, each Oxygen (O) has 6, and Hydrogen (H) has 1. Therefore, the total is:
Total = 4 (C) + 6 (O) × 3 (O) + 1 (H) × 2 (H) = 4 + 18 + 2 = 24 valence electrons.
1. Start with the Carbon atom in the center, as it is less electronegative than oxygen.
2. Attach two Oxygen atoms with single bonds to Carbon to represent the two hydroxyl groups.
3. Attach a double bond to the remaining Oxygen atom.
4. Place the Hydrogen atoms around the respective Oxygen atoms. This gives:
Now, we can determine the bond orders:
- Carbon-Oxygen double bond: bond order = 2
- Carbon-Oxygen single bonds (two): bond order = 1
Total bond orders show strong interactions within the molecule, with one double bond and two single bonds.
b) Phosphoric Acid (H₃PO₄)
Next, for phosphoric acid, we also start with the total valence electrons: Phosphorus (P) has 5 valence electrons, Oxygen (O) has 6, and Hydrogen (H) has 1. Therefore:
Total = 5 (P) + 6 (O) × 4 (O) + 1 (H) × 3 (H) = 5 + 24 + 3 = 32 valence electrons.
1. Place the Phosphorus atom in the center.
2. Connect it to four Oxygen atoms.
3. Three of those will have single bonds (with the Hydrogen atoms connected respectively), and one will have a double bond using the remaining electrons for bond formation. This gives:
Here are the bond orders:
- Phosphorus-Oxygen double bond: bond order = 2
- Phosphorus-Oxygen single bonds (three): bond order = 1
This results in a mix of bond types, crucial for the stability and reactivity of the molecule.