Question

Below is the Lewis structure of the formaldehyde (CH 2

​
O) molecule. ::
::
​
Count the number of bonding pairs and the number of lone pairs around carbon atom in this molecule. How many valence electrons are in the acetate ion C 2
​
H 3
​
O 2
−
​
? Decide whether these proposed Lewis structures are reasonable.

Answer 1

step 1: Counting Bonding Pairs and Lone Pairs around Carbon Atom

Carbon (C) Atom in Formaldehyde (CH₂O):

Carbon has 4 valence electrons.

In the Lewis structure of formaldehyde, there are 2 single bonds between carbon and hydrogen (CH₂ ) and 1 double bond between carbon and oxygen (CO).

Each single bond represents 2 electrons (1 bonding pair), and the double bond represents 4 electrons (2 bonding pairs).

Counting the bonding pairs around carbon:

2 bonding pairs with hydrogen (2 pairs * 2 electrons/pair = 4 electrons).

2 bonding pairs with oxygen (2 pairs * 2 electrons/pair = 4 electrons).

Total bonding pairs around carbon = 4 (2 from hydrogen + 2 from oxygen).

Lone Pairs around Carbon in Formaldehyde:

Lone pairs are unshared electron pairs.

In formaldehyde, there are no lone pairs around the carbon atom.

Step 2: Valence Electrons in Acetate Ion (C₂H₃O₂−)

Acetate Ion (C₂H₃O₂ −):

The acetate ion has two carbon atoms, three hydrogen atoms, and two oxygen atoms with a charge of -1.

Counting valence electrons:

2 carbon atoms = 4 electrons each * 2 = 8 electrons.

3 hydrogen atoms = 1 electron each * 3 = 3 electrons.

2 oxygen atoms = 6 electrons each * 2 = 12 electrons.

Adding the charge of -1 adds an extra electron.

Total valence electrons in the acetate ion = 8 (from carbon) + 3 (from hydrogen) + 12 (from oxygen) + 1 (from the charge) = 24 electrons.

Step 3: Analyzing Proposed Lewis Structures

Formaldehyde Lewis Structure Analysis:

The Lewis structure for formaldehyde (CH₂O) is reasonable based on the octet rule.

Carbon has a total of 4 bonding pairs (no lone pairs), fulfilling its octet by sharing electrons with hydrogen and oxygen.

Acetate Ion (C₂H₃O₂−) Lewis Structure Analysis:

The proposed structure should satisfy the octet rule and consider the charge on the ion.

A valid structure should distribute the 24 valence electrons such that all atoms follow the octet rule and the overall charge is accounted for.

Conclusion:

The number of bonding pairs around carbon in formaldehyde is 4 (with no lone pairs).

The acetate ion (C₂H₃O₂−) contains 24 valence electrons, and a reasonable Lewis structure should distribute these electrons to satisfy the octet rule and accommodate the ion's charge.

This breakdown should help you understand the steps involved in determining the bonding pairs, lone pairs, valence electrons, and the reasonableness of proposed Lewis structures for formaldehyde and the acetate ion.

Answer 2

In formaldehyde, the carbon atom has four bonding pairs and no lone pairs. The acetate ion has a total of 24 valence electrons, which satisfies the octet rule, making its proposed Lewis structure acceptable.

The Lewis structure of formaldehyde (CH₂O) shows carbon (C) bonded to two hydrogen (H) atoms with single bonds and one oxygen (O) atom with a double bond. Around the carbon atom, there are four bonding pairs (two from the double bond and one from each single bond), and there are no carbon atom lone pairs. Rationalizing the Lewis structure of the acetate ion (C₂H₃O₂⁻), carbon atoms typically make four bonds including any double or triple bonds. The number of valence electrons in the acetate ion is calculated by adding the valence electrons of all the atoms and accounting for the extra electron from the negative charge. This would be 4 for each carbon (total of 8), plus 1 for each hydrogen (total of 3), plus 6 for each oxygen (total of 12), plus 1 for the negative charge, equaling 24 valence electrons. This conforms to the octet rule, making the structures reasonable and acceptable.