E. Water: The Versatile Molecule
➢ In water, electrons are not shared equally in the bonds between hydrogen and oxygen
- Hydrogen atoms have a partial positive charge while oxygen atoms has a partial negative charge
■ Water is polar
➢ Hydrogen bonds
- Weak attractions that result of water’s polarity
■ Positive end of another polar molecule attracted to oxygen negative charge, and vice versa with the hydrogen end
■ Hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom
■ Weak Individually, but strong on a larger scale
- Lends watermany special properties
■ Cohesion
● Tendency for water to stick to water
● Important during transpiration - Water evaporates, pulls other water molecules with it, pulling all the way down from leaves to roots
■ Adhesion
● Tendency of water to stick to other substances
● $\text{Cohesion + Adhesion =}$ capillary action - Allows water to flow up roots/trunks/branches of trees in thin vessels
■ Surface tension
● Results from cohesion of water molecules
● Ex. water striders can sit on top of water without sinking
■ High heat capacity
● Heat Capacity=ability of a substance to resist temperature changes
● Keeps ocean temperatures stable
● Allows organisms to keep constant body temperature, since most life
forms are mostly made up of water
● Heat is absorbed when hydrogen bonds break, released when hydrogen bonds form
■ High heat of vaporization
● Heat a liquid must absorb for 1g to be converted to gas
● Evaporative cooling - As a liquid evaporates, its remaining surface cools
■ How sweat works to cool body down
■ Expansion on freezing
● Lattice structure of ice causes water to expand on freezing
● Allows ice to float on top of lakes in winter - Animal life can live beneath ice
■ Versatility as a solvent
● Solution is a liquid that is a homogenous mix of substances
● Solvent is the dissolving agent of a solution
● Solute is the substance that is dissolved
● Aqueous solution is one where water is the solvent
● Polarity of water allows it to be a versatile solvent - Can form hydrogen bonds easily
● Hydrophobic substances do not dissolve in water, but hydrophilic ones will