Q.46 What is the maximum number of hydrogen bonds that a water molecule can
make in the liquid state?
A water molecule can form a maximum of four hydrogen bonds in the liquid state through its two hydrogen atoms as donors and two lone pairs on oxygen as acceptors. This capability arises from water’s polar bent structure, enabling a tetrahedral arrangement despite dynamic fluctuations in liquid water. For CSIR NET aspirants, understanding this distinguishes maximum potential from average bonds (around 3.5).
Question Breakdown
CSIR NET Life Sciences Q.46 asks: “What is the maximum number of hydrogen bonds that a water molecule can make in the liquid state?” Options are typically 1, 2, 3, or 4. The key lies in water’s molecular geometry: oxygen’s sp³ hybridization yields two O-H bonds and two lone pairs, allowing four bonds—one per site.
Option Analysis
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Option 1: Incorrect; one bond ignores water’s two hydrogens and two lone pairs, possible only in extreme isolation.
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Option 2: Incorrect; accounts for either donor (two H) or acceptor (two lone pairs) sites but not both, underestimating full capacity.
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Option 3: Incorrect; reflects average bonds in liquid water (~3.5 at 25°C) due to thermal motion breaking some links, not the maximum.
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Option 4 (Correct): Matches structural maximum; each water links to four neighbors tetrahedrally, as in ideal network.
Molecular Structure
Water (H₂O) features oxygen bonded to two hydrogens at 104.5° angle, with two lone pairs. Each H donates one bond to another’s oxygen; each lone pair accepts one from another’s H, totaling four. In liquid state, bonds form/break rapidly (picoseconds), but maximum remains four per simulations and models like TIP4P.
Liquid vs. Ice Bonding
Ice achieves four bonds perfectly, forming a rigid lattice (density lower). Liquid water retains potential for four but averages fewer (~3.6 at 0°C, 3.2 at 100°C) from kinetic energy disrupting order. Question specifies “maximum,” so four applies.
Biological Relevance
Hydrogen bonding drives water’s high boiling point, cohesion, and solvent power, vital for life sciences like protein folding and DNA stability. CSIR NET emphasizes this for biochemistry/ecology units.
