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Multiple Choice
Which of the following is the correct Lewis dot structure for formaldehyde (CH2O)?
A
O atom triple bonded to C, C single bonded to two H atoms; O has one lone pair.
B
O atom double bonded to C, C single bonded to two H atoms; all atoms have complete octets except H.
C
O atom double bonded to C, C double bonded to one H and single bonded to the other H.
D
O atom single bonded to C, C single bonded to two H atoms; O has three lone pairs.
Verified step by step guidance
1
Identify the total number of valence electrons available for formaldehyde (CH2O). Carbon has 4 valence electrons, each hydrogen has 1, and oxygen has 6. Sum these to get the total valence electrons.
Determine the skeletal structure of the molecule. Carbon is the central atom bonded to two hydrogens and one oxygen atom.
Start by placing single bonds between carbon and each hydrogen and between carbon and oxygen. Each single bond accounts for 2 electrons.
Complete the octet for the oxygen atom by adding lone pairs. Since oxygen typically forms two bonds and has two lone pairs, adjust bonding to form a double bond between carbon and oxygen to satisfy the octet rule for both atoms.
Verify that all atoms (except hydrogen, which follows the duet rule) have complete octets and that the total number of electrons used equals the total valence electrons calculated initially.