To draw the Lewis structure for sulfur dioxide (SO2), you start by counting the total number of valence electrons. Sulfur (S) has 6 valence electrons, and each oxygen (O) has 6 valence electrons. Therefore, the total number of valence electrons for SO2 is:
Total Valence Electrons = 6 (S) + 6 (O) + 6 (O) = 18 valence electrons
Next, we sketch a structure where the sulfur atom is the central atom, bonded to the two oxygen atoms. We can form double bonds between sulfur and each oxygen atom to satisfy the octet rule for oxygen, as shown below:
O || O=S
This configuration uses 4 electrons (2 for each double bond) to bond with oxygen. Since each oxygen atom has 6 valence electrons and is involved in a double bond, both oxygens will have 2 lone pairs of electrons remaining (4 electrons total for both oxygens):
O: || O=S :O
Now, we check for formal charges. The formal charge is calculated using the formula:
Formal Charge = Valence Electrons – (Non-bonding Electrons + 0.5 * Bonding Electrons)
For sulfur:
– Valence Electrons = 6
– Non-bonding Electrons = 0
– Bonding Electrons = 8 (4 from each double bond)
Formal Charge for sulfur = 6 – (0 + 0.5 * 8) = 0
For each oxygen:
– Valence Electrons = 6
– Non-bonding Electrons = 4 (2 lone pairs)
– Bonding Electrons = 4 (2 from the double bond)
Formal Charge for oxygen = 6 – (4 + 0.5 * 4) = 0
Hence, all atoms in SO2 have a formal charge of 0.
Now, looking at the geometry of the molecule, SO2 has a bent shape due to the presence of lone pairs on the sulfur atom and the two bonding regions which gives an angle of approximately 120 degrees.
Finally, when considering polarity, the molecule is polar. This is due to the difference in electronegativity between sulfur and oxygen, leading to a dipole moment. The bent shape prevents the dipole moments from cancelling each other out.
In summary:
- Total Valence Electrons: 18
- Lewis Structure: SO2 with two double bonds.
- Formal Charges: 0 on each atom.
- Overall Shape: Bent.
- Molecule Polarity: Polar.