Draw the Lewis structure for the polyatomic formate CHO-, anion Be sure to include all resonance structures that satisfy the octet rule 2

The Correct Answer and Explanation is:

Lewis Structure of Formate Ion (CHO⁻) – Including Resonance Structures

Step-by-step Lewis structure drawing:

Count total valence electrons:
- Carbon (C): 4 valence electrons
- Hydrogen (H): 1 valence electron
- Oxygen (O): 6 valence electrons
- Extra 1 electron due to the negative charge
  Total = 4 + 1 + 6 + 1 = 12 valence electrons
Skeleton structure:
The carbon is the central atom, bonded to both hydrogen and oxygen:
H–C–O⁻ or H–C=O⁻ depending on bonding.
Distribute electrons to satisfy octets and charges:
The carbon forms a single bond with hydrogen and two bonds with oxygen, but due to resonance, there are two valid resonance structures.

Resonance Structures for CHO⁻:

Structure 1:

     ..
H–C=O⁻
     ..

Carbon is single-bonded to hydrogen and double-bonded to oxygen.
The oxygen bears a negative charge and has two lone pairs.

Structure 2:

     ..
H–C⁻–O
     ::

Carbon is single-bonded to hydrogen and oxygen.
The carbon bears the negative charge, and the oxygen has a full octet with two lone pairs and a single bond.

However, Structure 2 violates the octet rule on carbon (carbon has only 6 electrons here), so it is not valid.

Instead, we consider the correct CHO⁻ resonance hybrid, which involves two resonance forms where the negative charge is delocalized between the carbon and oxygen via the C–O double bond rotating.

Correct Resonance Structures:

H–C=O⁻ (with oxygen bearing negative charge, two lone pairs)
[H–C⁻≡O⁺] (rare, less stable, formal charge imbalance)

But the only valid octet-satisfying resonance structure is:

   ..
H–C=O⁻
   ..

Final Answer:

Only one major Lewis structure for formate (CHO⁻) satisfies the octet rule:

H–C=O⁻
   ..

The hydrogen is bonded to carbon, carbon forms a double bond with oxygen, and oxygen bears a negative charge with a full octet. The formal charges are:

H: 0
C: 0
O: –1

Explanation:

The formate ion (CHO⁻) is a simple polyatomic anion derived from formic acid. When drawing its Lewis structure, the goal is to distribute the 12 valence electrons such that all atoms (except hydrogen) satisfy the octet rule and the formal charges are minimized.

Carbon is the central atom because it can form four bonds. Hydrogen can only form one bond, so it must be directly bonded to carbon. The oxygen atom, being more electronegative, is placed terminally and can accept lone pairs and extra electrons.

The most stable and valid Lewis structure shows a single bond between hydrogen and carbon, and a double bond between carbon and oxygen. The oxygen atom retains two lone pairs and carries the extra negative charge, resulting in a formal charge of –1 on oxygen. Carbon and hydrogen both have formal charges of zero.

Although resonance is often present in oxyanions like carboxylate (e.g., HCOO⁻), in the case of formate (CHO⁻), there is only one major resonance structure that satisfies the octet rule for all atoms. Some textbooks may show a second form involving a triple bond or a lone pair on carbon, but these either violate the octet rule or are significantly less stable due to high formal charge separation. Therefore, only the structure with a carbon-oxygen double bond and a negatively charged oxygen is typically accepted.

This structure also aligns with experimental observations, such as bond lengths and reactivity patterns. In sum, CHO⁻ has one main Lewis structure: H–C=O⁻, with the oxygen atom bearing the negative charge and all atoms satisfying the octet rule.