1.2 Structure of Water & Hydrogen Bonding

Water’s polarity

• oxygen is very electronegative - “hogs electrons”

result

• hydrogens have partial POSITIVE charge

• oxygen has partial NEGATIVE charge

Hydrogen Bonds

• weak bonds resulting from electrostatic attraction b/w molecules

• direct result of polarity of water

Water as a solvent

• the polarity of water makes it a great solvent

• “universal solvent”

• dissolves many things - polar mlc., ionic mlc., NOT non-polar mlc.

  • ex. NaCl (ionic)

Cohesion

attraction of LIKE particles

Adhesion

attraction of DIFFERING particles

Hydrophilic

“water-loving”

Hydrophobic

“water-fearing”

Capillary Action

act of water moving through a narrow tube against the force of gravity

Results from

1. cohesion (surface tension)

2. adhesion

Increased by

1. Narrowing tube’s diameter

2. Increasing the hydrophilicity of the tube

BPQ

If a tube shows capillary action in water, then in mercury the opposite effect will be observed. From this what can we infer about the properties of mercury?

The tube is hydrophilic, therefore mercury must be hydrophobic.

Surface Tension

• enhancement of intermolecular forces on the surface

• water molecules are more likely to form hydrogen bonds parallel to the surface

Heat Capacity

• amount of energy needed to produce a change in temperature

• water has a very high heat capacity because you need extra energy to break its hydrogen bonds

Temperature

high avg. kinetic energy = hot

low avg. kinetic energy = cold

Evaporation

• process where water transitions from liquid to gas at the surface

• results in a drop in temp. of the remaining liquid (evaporative cooling)

• molecules with higher avg. kinetic energy evaporate

more evaporation = cooler

Evaporative Cooling

bc the average kinetic energy is higher at the surface, as it evaporates, heat is lost and the leftover fluid is cooler

Transpiration

• evaporation of water from plant tissue

• water replaced thru plant’s roots & stems

BPQ

What property of water allows

water to flow from the roots to

the leaves?

Capillary action allows water to flow from roots to leaves

Ice

• less dense than water - floats!

• water expands as it freezes