Draw a Lewis structure for SeBr2O in which all atoms obey the octet rule.
Do not draw double bonds to oxygen unless they are needed in order for the central atom to obey the octet rule.
The correct answer and explanation is:
To draw the Lewis structure for SeBr₂O, we need to follow the steps to ensure that all atoms obey the octet rule (except for elements that can accommodate more than 8 electrons, like sulfur, phosphorus, and selenium). Let’s walk through the structure and then explain the reasoning.
Step 1: Count the total number of valence electrons.
- Selenium (Se) is in Group 16, so it has 6 valence electrons.
- Bromine (Br) is in Group 17, and there are two bromine atoms, so 2 × 7 = 14 valence electrons.
- Oxygen (O) is also in Group 16, so it has 6 valence electrons.
Total valence electrons = 6 (Se) + 14 (Br₂) + 6 (O) = 26 valence electrons.
Step 2: Choose a central atom.
- Selenium (Se) is the least electronegative element and is the central atom in the structure.
- The other atoms (Br and O) will be placed around Se.
Step 3: Draw the skeleton structure.
- Connect Se to two Br atoms and one O atom using single bonds. Each single bond counts as 2 electrons.
Step 4: Distribute remaining electrons.
- After forming single bonds between Se and Br₂, and Se and O, we used 6 electrons (3 bonds × 2 electrons).
- Remaining electrons = 26 – 6 = 20 electrons.
- Distribute these electrons as lone pairs. First, place lone pairs on the surrounding atoms (Br and O).
- Each Br will have 6 electrons remaining to complete its octet (since each bond uses 2 electrons).
- Oxygen, with 2 bonds to Se, will have 4 remaining electrons to complete its octet.
Step 5: Final adjustment to ensure Se obeys the octet rule.
- Selenium, with 2 bonds to Br and 1 bond to O, initially has 6 electrons around it. Therefore, it needs 2 more electrons to complete its octet.
- Place a lone pair on selenium to complete its octet.
Final Lewis Structure of SeBr₂O:
Br
|
Se -- O
|
Br
Explanation:
- Electron Count: We used all 26 valence electrons. Each Br has 6 electrons, O has 6, and Se has 8 electrons, fulfilling the octet rule.
- Octet Rule: Both oxygen and the two bromine atoms have a full octet (8 electrons). Selenium, being in the 4th period, can hold more than 8 electrons, but here, it still obeys the octet rule due to the lone pair of electrons added to it.
- Formal Charge: All atoms have a formal charge of 0, which indicates that this is the most stable arrangement of electrons for SeBr₂O.
This structure ensures that all atoms obey the octet rule (or can satisfy expanded octets for selenium) and utilizes all the available valence electrons efficiently.