Why is the bond angle in water 104.5° and not 109.5°?

Water (H₂O) has sp³ hybridized O atom with 2 bond pairs (O−H) and 2 lone pairs. Lone pair-lone pair repulsion > lone pair-bond pair > bond pair-bond pair. The two lone pairs compress the H−O−H bond angle from the ideal tetrahedral 109.5° to 104.5°.

What is resonance and give one example?

Resonance occurs when a single Lewis structure cannot adequately represent a molecule — the actual structure is a hybrid of two or more Lewis structures (resonance structures). Example: Ozone (O₃) is represented by two resonance structures with the double bond alternating between the two O−O bonds. The actual O−O bond length is intermediate between single and double bond.

Why does ice float on water?

In ice, each water molecule forms 4 hydrogen bonds in a tetrahedral, open lattice structure. This cage-like structure makes ice less dense (0.917 g/cm³) than liquid water (1 g/cm³) which has a more compact arrangement. Therefore ice floats on water — which is crucial for aquatic life survival in winters.

Types of Chemical Bonds

Chemical Bonding and Molecular Structure • Class 11 Chemistry • NCERT • CBSE

Chemical bonds: Ionic bonds (complete electron transfer — NaCl), Covalent bonds (electron sharing — H₂, Cl₂), Coordinate bonds (both electrons from one atom — NH₄⁺). Bond polarity depends on electronegativity difference. Hybridization: sp (linear), sp² (trigonal planar), sp³ (tetrahedral).

Frequently Asked Questions

Why is the bond angle in water 104.5° and not 109.5°?: Water (H₂O) has sp³ hybridized O atom with 2 bond pairs (O−H) and 2 lone pairs. Lone pair-lone pair repulsion > lone pair-bond pair > bond pair-bond pair. The two lone pairs compress the H−O−H bond angle from the ideal tetrahedral 109.5° to 104.5°.
What is resonance and give one example?: Resonance occurs when a single Lewis structure cannot adequately represent a molecule — the actual structure is a hybrid of two or more Lewis structures (resonance structures). Example: Ozone (O₃) is represented by two resonance structures with the double bond alternating between the two O−O bonds. The actual O−O bond length is intermediate between single and double bond.
Why does ice float on water?: In ice, each water molecule forms 4 hydrogen bonds in a tetrahedral, open lattice structure. This cage-like structure makes ice less dense (0.917 g/cm³) than liquid water (1 g/cm³) which has a more compact arrangement. Therefore ice floats on water — which is crucial for aquatic life survival in winters.

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