Crash Course on the Properties of Water

Introduction

• Water is unique as it naturally occurs in solid, liquid, and gas forms on Earth.
• Life on Earth depends on water; scientists search for water elsewhere in the universe to find signs of life.
• Discovery of gypsum on Mars by rover Opportunity indicates past presence of water, exciting possibilities for life.

Molecular Structure of Water

• Water molecule is H2O: two hydrogen atoms covalently bond with one oxygen atom.
• Water molecules are V-shaped due to oxygen being more electronegative than hydrogen.
• This creates polarity: oxygen has a slight negative charge, hydrogen has a slight positive charge.

Hydrogen Bonds

• Polarity leads to hydrogen bonding between water molecules.
• Hydrogen bonds are weak but crucial for many properties of water.
• Properties include high cohesion and surface tension.

Cohesion and Surface Tension

• Cohesion: attraction between like molecules (water to water).
• Water has high cohesion, the highest of any non-metallic liquid.
• Surface tension allows insects and even some animals to walk on water.

Adhesion

• Adhesion: attraction between different substances (e.g., water to glass).
• This can lead to capillary action, where water can defy gravity and climb up structures like straws.

Water as a Solvent

• Water is an excellent solvent, capable of dissolving more substances than any other liquid.
• Polar substances dissolve in water (hydrophilic), non-polar substances do not (hydrophobic).
• This property allows water to carry nutrients and waste in biological systems.

Historical Context: Henry Cavendish

• Cavendish identified hydrogen gas and determined the composition of water.
• Despite his eccentric nature, he made significant scientific discoveries.
• Known for recognizing hydrogen's properties and performing groundbreaking experiments with simple tools.

Unique Properties of Ice

• Unlike other substances, ice (solid water) is less dense than liquid water.
• Hydrogen bonds form a crystalline structure, spacing molecules apart and allowing ice to float.
• If ice sunk, it would severely disrupt ecosystems and global water levels.

Heat Capacity

• Water has a high heat capacity, meaning it absorbs and retains heat well.
• This regulates climate and temperature on Earth, making coastal areas more temperate.
• Evaporation cools surfaces (e.g., sweating helps regulate body temperature).

Conclusion

• Water's unique properties are vital for life and environmental stability.
• Review these concepts to understand water's role in natural processes and life on Earth.

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Review these notes to prepare for any upcoming tests or to reinforce your understanding of water's critical functions.