WATER

Life probably originated in water 3.8 billion years ago

Life spread from the oceans to the continents about 500 million years ago.

Still water is quintessential for life All biochemical reactions happen in aqueous

milieu

Water - the elixir of life

only known substance that can naturally exist as a gas, a liquid, and solid 

This unique property of water is due to Hydrogen bond

Diamond is non-polar

Methane too is Non polar

Water is polar

CO2 and CCl4 are non polar

Hydrogen Bond

Hydrogen Bond

•Weak bonds – Energy: 20 kJ mol–1

• O—H bond : 460 kJ mol–1

• C—H bond : 410 kJ mol–1

• Life span: pico seconds

Why only Water ?

Ice Floats in water

Hydrogen bond in ice

Implications

Cryoablation

Water molecules are so small so many of them can associate with the solute to make them soluble.

Water Is an Excellent Solvent

Not only electrolytes….

Water of hydration

• Full saturation•Half saturation

Binding to zinc lowers the pKa of water from 15.7 to 7

Nonpolar Substances Are Insoluble in Water

Why egg takes longer time to boil at higher altitudes ?

Properties of Water

• Cohesion• Adhesion• High Specific Heat• High Heat of Vaporization• Less Dense as a Solid

Cohesion

• Attraction between particles of the same substance

• Results in Surface tension

Surface Tension

Helps insects walk across water

Adhesion

• Attraction between two different substances.• Water will make hydrogen bonds with other surfaces

such as glass, soil, plant tissues, and cotton.

• Example: transpiration process which plants and trees remove water from the soil, and paper towels soak up water.

Adhesion Causes Capillary Action

Which gives water the ability to “climb”

structures

How does the water in earthen pot becomes cool ?

Water Is Nucleophilic

• oxygen atom of water has two unshared pairs of electrons making it nucleophilic.

• As water is abundant inside the cells, Many macromolecules should be easily degraded by nucleophilic attack by water.

Ionization of Water

• Important properties of water is its slight tendency to ionize

Hydrogen Bond

Hydrogen Bond

Van der Waals Interactions