Hydrogen bonding gives water high boiling point, high heat capacity and lower-density ice.
Practise Bonding & Molecular Structure All Bonding & Molecular Structure topics
Water has several unusual properties that deviate from the trends predicted for hydrides of other elements in its group, and these arise mainly from extensive hydrogen bonding. Its high boiling point, high heat capacity and high surface tension all reflect the energy needed to break its network of hydrogen bonds. Water is densest at 4 degrees Celsius, and ice is less dense than liquid water because its hydrogen bonds hold the molecules in an open hexagonal lattice. This is why ice floats and lakes freeze from the top down, protecting aquatic life. These properties make water essential for life and for its role as a solvent.
Key ideas: Key numbers: density maximum at 3.98 C, heat of vaporization 40.7 kJ/mol, specific heat 4.18 J per g per K, high dielectric constant near 80, and ice expands about 9 percent on freezing. Each water molecule in ice has four hydrogen bonds in a tetrahedral arrangement, and in the liquid about 3.4 on average.
Common mistakes and connections: Common mistakes are saying ice is less dense because molecules are heavier or lighter, or thinking that water has the highest boiling point of all liquids. Also, hydrogen bonding does not entirely stop when water melts: only about 15 percent are broken. Links to hydrogen bonding, climate, solvent properties and biological membranes.
Water is densest at 4 C, not at its freezing point, a consequence of its hydrogen-bond network; ice floats. The interactive lesson shows this as a live animation or chart.
Water boils at 100 degrees Celsius, whereas hydrogen sulfide, with weaker hydrogen bonding, boils at about -60 degrees Celsius.
Hydrogen bonding gives water high boiling point, high heat capacity and lower-density ice.
Water's Anomalous Properties is a intermediate topic in Bonding & Molecular Structure. It builds on the vocabulary of beginner topics in this area.
Study these earlier topics in Bonding & Molecular Structure first: Dipole-Induced Dipole Forces, Boiling Point and Intermolecular Forces, Intramolecular Hydrogen Bonding.
The next topics in Bonding & Molecular Structure are Covalent Network Solids and Molecular Solids.
Yes. The interactive lesson includes a self-check question on Water's Anomalous Properties, and the Bonding & Molecular Structure quiz draws on every topic in this area.
Water's Anomalous Properties is topic 78 of 104 in Bonding & Molecular Structure.