To draw the Lewis structures for SF6 and N2O4, we need to follow a series of steps that include counting valence electrons, arranging the atoms, and distributing the electrons accordingly.
Lewis Structure for SF6
1. **Count the Valence Electrons:** Sulfur (S) has 6 valence electrons and each fluorine (F) atom has 7 valence electrons. Since there are 6 fluorine atoms, we have:
- 1 S: 6 electrons
- 6 F: 6 × 7 = 42 electrons
So, total valence electrons = 6 + 42 = 48.
2. **Arrange the Atoms:** Place Sulfur at the center and surround it with 6 Fluorine atoms.
3. **Distribute Electrons:** Each S-F bond uses 2 electrons. Thus, 6 bonds consume 12 electrons. The remaining electrons (48 – 12 = 36) are placed as lone pairs on the fluorine atoms until each has a complete octet.
Final Lewis structure shows sulfur with 6 bonds and no formal charge, satisfying the octet rule for all fluorine atoms.
Lewis Structure for N2O4
1. **Count the Valence Electrons:** Nitrogen (N) has 5 valence electrons, and Oxygen (O) has 6 valence electrons. Therefore:
- 2 N: 2 × 5 = 10 electrons
- 4 O: 4 × 6 = 24 electrons
Total valence electrons = 10 + 24 = 34.
2. **Arrangement of Atoms:** A linear arrangement can be assumed with N in the center and O atoms on the sides. We may start with a structure where one nitrogen atom is bonded to two oxygen atoms and the other nitrogen is bonded to the remaining two oxygen atoms.
3. **Distributing Electrons:** Draw single bonds first, then add lone pairs to fulfill the octet for the oxygen atoms. We find that 2 of the oxygens can form double bonds with nitrogen to minimize formal charge.
Based on formal charges, the most stable resonance structures involve two N=O double bonds and two N-O single bonds.
Formal Charge Analysis
Evaluate the formal charges for each atom in the resonance structures. The structure with zero formal charges or the least formal charge on the most electronegative atoms is generally preferred.
- Formal charge formula: Formal Charge = Valence Electrons – (Non-bonding Electrons + 1/2 Bonding Electrons)
By calculating the formal charges in the various resonance forms of N2O4, we can determine the most stable structure that has minimal formal charges.