Crash Course Biology: Properties of Water

Introduction

• Water is unique as it naturally occurs in all three forms: solid, liquid, and gas.
• Essential for life; search for life elsewhere often begins with the search for water.
• Exciting discoveries like Mars' Opportunity rover finding gypsum veins suggest past water presence.

Structure of Water

• Chemical structure: H2O (two hydrogen atoms bonded to one oxygen atom).
• Water molecules are V-shaped due to the covalent bonds.
• Oxygen has a slight negative charge; hydrogen has a slight positive charge, creating polarity.

Hydrogen Bonds

• Polarity leads to hydrogen bonds between water molecules.
• Hydrogen bonds are vital for many of water's properties.
• Cohesion: attraction between water molecules.
  • Results in high surface tension.
  • Allows insects and objects to "walk" on water.

Adhesion and Capillary Action

• Adhesion: attraction between water molecules and different substances (e.g., water and glass).
• Capillary action: water can climb against gravity in narrow spaces due to adhesion and cohesion.

Solvent Properties

• Water is known as the "universal solvent."
• Dissolves more substances than other liquids.
• Polar substances (hydrophilic) dissolve, forming hydrogen bonds.
• Non-polar substances (hydrophobic) do not dissolve due to water’s cohesive forces.

Historical Context: Henry Cavendish

• First to recognize hydrogen gas as distinct and determine water's composition.
• Discovered the composition of the atmosphere and the density of the Earth.
• Might have had autism; eccentric personality.

Unique Properties of Ice

• Ice floats because solid water is less dense than liquid water.
• Hydrogen bonds form a crystalline structure in ice, spacing molecules apart.
• Floating ice prevents aquatic ecosystems from freezing entirely.

Heat Capacity

• Water's high heat capacity helps it regulate climate.
• Oceans act as heat sinks, moderating temperature extremes.
• Water retains heat well, making it essential for temperature regulation in various contexts.

Evaporation and Cooling

• Evaporation of water from the skin cools the body.
• Sweating is an effective cooling mechanism due to evaporation taking heat.

Summary

• Water's properties make it essential for life and unique among substances.
• Encouragement to review material for better understanding and exam preparation.