Which is the correct Lewis structure for carbonic acid, H2CO3? 6-H 0-H :O=C :O=C 0-H 0-H :O-H 6=C 0-H 0-H 0=C 0-H IV O1 O1 O1 O1
The Correct Answer and Explanation is:
Correct Lewis Structure for Carbonic Acid (H₂CO₃):
The correct Lewis structure for carbonic acid is:
mathematicaCopyEdit O
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H–O–C–O–H
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O
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H
More precisely, in Lewis structure format:
- The central atom is carbon (C).
- The carbon atom forms one double bond with one oxygen atom (O), and two single bonds with two –OH groups (hydroxyl groups).
Here is a detailed representation:
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H–O–C–O–H
Or in terms of lone pairs and bonds:
- One oxygen forms a double bond with carbon and has two lone pairs.
- Two other oxygens are each bonded to hydrogen (O–H), forming hydroxyl groups. Each of these oxygens has two lone pairs.
- Carbon forms four bonds total (satisfying its octet rule).
- Each hydrogen is bonded to an oxygen.
Textbook-Style Explanation (300+ words):
Carbonic acid (H₂CO₃) is a weak diprotic acid formed when carbon dioxide dissolves in water. Understanding its Lewis structure involves applying key principles of chemical bonding, such as the octet rule, formal charges, and electron pair geometry.
The molecule contains 2 hydrogen atoms, 1 carbon atom, and 3 oxygen atoms. Carbon is the central atom because it is the least electronegative (excluding hydrogen). Carbon has 4 valence electrons and typically forms 4 covalent bonds to satisfy the octet rule. Oxygen has 6 valence electrons and prefers to form 2 bonds. Hydrogen has 1 valence electron and forms only 1 bond.
In carbonic acid, the carbon atom is double bonded to one oxygen atom (C=O) and single bonded to two other oxygen atoms. Each of the single-bonded oxygen atoms also bonds to a hydrogen atom, forming hydroxyl groups (–OH). This configuration allows each atom to achieve a stable octet configuration (except hydrogen, which follows the duet rule).
This structure ensures all atoms have a formal charge of zero or close to zero, making it the most stable and commonly accepted Lewis structure. Each oxygen has the appropriate number of lone pairs to complete their octet.
Importantly, this molecule is not linear but bent around the central carbon due to the spatial arrangement of its atoms. The double-bonded oxygen is usually placed opposite one of the hydroxyl groups to minimize repulsion, giving the molecule a somewhat trigonal planar geometry around the central carbon atom.
Carbonic acid plays an important role in biological systems, particularly in buffering blood pH and in forming carbonates and bicarbonates in aqueous systems. The Lewis structure is fundamental to understanding its acid-base behavior, reactivity, and interactions in chemical reactions.
