Multiple Choice
In the Lewis dot structure of the neutral compound BCl_3, how many lone pairs are present on the central boron atom? Express your answer numerically as an integer.
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11. Bonding & Molecular Structure
Lewis Dot Structures: Neutral Compounds
Multiple Choice
Which of the following is the correct Lewis dot structure for formaldehyde (CH2O)?
A
O=C(H)2, where the oxygen atom is double-bonded to carbon and has two lone pairs, and each hydrogen is single-bonded to carbon.
B
O–C(H)2, where the oxygen atom is single-bonded to carbon and has three lone pairs, and each hydrogen is single-bonded to carbon.
C
O–C(H)2, where the oxygen atom is single-bonded to carbon and has two lone pairs, and each hydrogen is double-bonded to carbon.
D
O≡C(H)2, where the oxygen atom is triple-bonded to carbon and has one lone pair, and each hydrogen is single-bonded to carbon.
Verified step by step guidance1
Step 1: Determine the total number of valence electrons available for bonding in formaldehyde (CH2O). Carbon has 4 valence electrons, each hydrogen has 1, and oxygen has 6. So, total valence electrons = 4 (C) + 2 × 1 (H) + 6 (O) = 12 electrons.
Step 2: Arrange the atoms with carbon as the central atom because it is less electronegative than oxygen and can form multiple bonds. Place the two hydrogens and one oxygen around the carbon.
Step 3: Connect the atoms with single bonds initially. Each single bond represents 2 electrons. So, connect carbon to each hydrogen and to oxygen with single bonds, using 6 electrons (3 bonds × 2 electrons each).
Step 4: Distribute the remaining electrons to satisfy the octet rule, starting with the more electronegative atom, oxygen. Place lone pairs on oxygen to complete its octet. Then, check if carbon has a complete octet; if not, form a double bond between carbon and oxygen by converting lone pairs into bonding pairs.
Step 5: Verify the Lewis structure by counting the total electrons used and ensuring each atom (except hydrogen, which follows the duet rule) has a full octet. The correct structure will have carbon double-bonded to oxygen with two lone pairs on oxygen, and single bonds between carbon and each hydrogen.
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