Draw the Lewis structure for the selenium dioxide (SeO2) molecule. Be sure to include all resonance structures that satisfy the octet rule.
The correct answer and explanation is:
Correct Lewis Structure of Selenium Dioxide (SeO₂):
Selenium dioxide has two valid resonance structures. Each structure shows selenium (Se) forming a double bond with one oxygen and a single bond with the other, where the singly bonded oxygen carries a negative formal charge and the selenium carries a positive formal charge.
Resonance Structure 1:
..
O = Se – O⁻
..Resonance Structure 2:
..
⁻O – Se = O
..Each oxygen atom has 6 valence electrons and needs two more to complete its octet. Selenium has 6 valence electrons. In both structures, formal charges are minimized and all atoms follow the octet rule.
Explanation (300 words):
Selenium dioxide (SeO₂) is a molecular compound consisting of one selenium atom and two oxygen atoms. To draw its Lewis structure, we begin by counting valence electrons. Selenium has 6 valence electrons, and each oxygen atom also contributes 6, giving a total of:
6 (Se) + 6×2 (O) = 18 valence electrons.
Next, we place selenium as the central atom because it is less electronegative than oxygen. We connect each oxygen to selenium using a single bond, using 4 electrons (2 for each bond). That leaves 14 electrons.
We distribute the remaining 14 electrons to complete the octets of the oxygen atoms. Each oxygen needs 6 more electrons (3 lone pairs), so 12 electrons are used to satisfy both oxygens. Two electrons remain, which can be placed as a lone pair on selenium.
However, in this configuration, selenium only has 6 electrons around it. To satisfy the octet rule, one of the lone pairs on an oxygen atom can be shared to form a double bond with selenium. This results in one double bond and one single bond, giving selenium 8 electrons.
Since either oxygen can form the double bond, two resonance structures exist:
- One where the left oxygen forms the double bond and the right oxygen holds a negative charge.
- One where the right oxygen forms the double bond and the left oxygen holds a negative charge.
In both structures, the molecule maintains overall charge neutrality, obeys the octet rule, and minimizes formal charges. These resonance structures explain the delocalization of electrons and the stability of the SeO₂ molecule.