Draw the Lewis structure of SeOF2 (by following the octet rule on all atoms) and then determine the ideal bonding angle(s) of the central atom. 90° and 120° B) 109.59° C) 60° D) 45° 90°
The Correct Answer and Explanation is:
To draw the Lewis structure of SeOF2 (selenium oxyfluoride) and determine the ideal bonding angle(s) for the central atom, we can follow these steps:
Step 1: Count the valence electrons
- Selenium (Se) is in Group 16, so it has 6 valence electrons.
- Oxygen (O) is also in Group 16, so it has 6 valence electrons.
- Fluorine (F) is in Group 17, and each fluorine atom has 7 valence electrons. Since there are two fluorine atoms, the total for fluorine is 2×7=142 \times 7 = 142×7=14 electrons.
Thus, the total number of valence electrons for SeOF2 is: 6(from Se)+6(from O)+14(from F2)=26 valence electrons6 (\text{from Se}) + 6 (\text{from O}) + 14 (\text{from F2}) = 26 \text{ valence electrons}6(from Se)+6(from O)+14(from F2)=26 valence electrons
Step 2: Draw the skeletal structure
- Selenium is the central atom, as it is less electronegative than oxygen or fluorine.
- Oxygen will be bonded to selenium, and fluorine will be bonded to selenium. We use single bonds to connect these atoms.
Step 3: Distribute electrons
- Each Se-F bond will use 2 electrons, and each Se-O bond will also use 2 electrons. So far, we’ve used:
2×2(for two Se-F bonds)+2×1(for Se-O bond)=6 electrons.2 \times 2 (\text{for two Se-F bonds}) + 2 \times 1 (\text{for Se-O bond}) = 6 \text{ electrons}.2×2(for two Se-F bonds)+2×1(for Se-O bond)=6 electrons.
This leaves us with 26−6=2026 – 6 = 2026−6=20 electrons to distribute.
- Place lone pairs on the oxygen and fluorine atoms. Oxygen will need 6 electrons to complete its octet, and each fluorine will need 6 electrons to complete its octet. Distributing the remaining 20 electrons:
- Oxygen gets 6 electrons in the form of three lone pairs.
- Each fluorine gets 6 electrons in the form of three lone pairs.
Thus, the Lewis structure looks like this:
rCopyEdit F
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Se--O
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F
Step 4: Determine the molecular geometry and bond angles
- The central atom, selenium, has three regions of electron density: one from the Se-O bond and two from the Se-F bonds.
- To minimize electron repulsion, the geometry of the molecule will adopt a trigonal pyramidal shape. This shape typically has bond angles close to 90° and 120° but slightly distorted due to the lone pairs on selenium.
Step 5: Ideal bonding angle
Given the geometry and electron repulsion considerations, the ideal bond angles for the central atom in this case are 90° and 120°, corresponding to option A.
Explanation:
- The Se atom in SeOF2 is surrounded by three bonding pairs and one lone pair of electrons, resulting in a trigonal pyramidal molecular shape.
- The ideal bond angles for a trigonal pyramidal structure are usually close to 90° and 120°, but they can be slightly less due to the lone pair.
Thus, the correct answer is A) 90° and 120°.
