• Shape: bent (V-shaped)
• Bond angle: about 104.5°

• Oxygen forms two covalent bonds with hydrogen.
• Bond length: about 0.096 nm.
• Oxygen also has two lone pairs of electrons.

• Oxygen attracts electrons more strongly than hydrogen.
• This makes oxygen slightly negative and hydrogens slightly positive.
• The molecule has a dipole moment (~1.85 D).

• Each water molecule can connect to others by hydrogen bonds.
• Each molecule can form up to 4 bonds (2 donor, 2 acceptor).
• This network explains many special properties of water.

• Melting point: 0 °C at 1 atm.
• Boiling point: 100 °C at 1 atm.
• Triple point: 0.01 °C, 611 Pa.
• Critical point: 374 °C, 22.1 MPa.

• Specific heat: high (~4.18 J·g⁻¹·K⁻¹).
• Heat of vaporization: high (~40.7 kJ·mol⁻¹).
• Heat of fusion: ~6.0 kJ·mol⁻¹.

• Water is densest at about 4 °C.
• Ice is less dense than liquid water, so it floats.

• Water dissolves salts and polar molecules easily.
• It does this by surrounding ions and molecules with hydration shells.
• Non-polar substances do not dissolve well in water.

• Two water molecules can react with each other.
• Equation: 2 H₂O ⇌ H₃O⁺ + OH⁻.
• At 25 °C: [H₃O⁺] = [OH⁻] = 10⁻⁷ M.

• Water can act as an acid (donates H⁺).
• Water can act as a base (accepts H⁺).

• Water breaks down into gases when electricity is passed through it.
• Equation: 2 H₂O → 2 H₂ + O₂.
• Hydrogen is formed at the cathode, oxygen at the anode.

• Water has high surface tension (~72 mN/m at 25 °C).
• This is due to hydrogen bonding between molecules.
• It allows droplets, capillary action, and meniscus formation.

• Water has moderate viscosity.
• Viscosity decreases when temperature increases.
• Water molecules diffuse quickly because of constant H-bond rearrangement.

• Relative permittivity (dielectric constant) ~80 at 25 °C.
• Pure water conducts electricity poorly.
• Conductivity increases when salts or ions are present.

• Refractive index: ~1.33.
• Strong absorption in infrared (O–H vibrations).

• Common form: Ice Ih (hexagonal lattice).
• Other forms exist at high pressure (Ice II, III, etc.).

• In gas phase, molecules rotate and vibrate freely.
• Water vapor strongly absorbs infrared radiation.

• Adding solutes lowers freezing point.
• Adding solutes raises boiling point.
• Solutes also create osmotic pressure (π = iMRT).

Water is bent and polar, forms hydrogen bonds, and shows high heat capacity, density anomaly, strong solvent action, and unique chemical reactivity.