A1.1.2 Hydrogen bonds as a consequence of the polar covalent bonds within water molecules: understand that polarity of covalent bonding with water molecules is due to unequal sharing of electrons and that hydrogen bonding due to this polarity occurs between water molecules. Be able to represent two or more water molecules and hydrogen bonds between them with notation shown below to indicate polarity.

Explanation:

• water is polar,

• H-bonds form between slightly negatively charged oxygen on one water molecule and slightly positively charged hydrogen of a different water molecules

• attraction between like molecules

• many H-bonds create strong cohesive forces

Examples:

• water can be pulled up xylem in long columns

• surface tension of water allows some insects to walk on water

Explanation:

• H-bonds between water molecules and other polar substances

Examples:

• Adhesion and cohesion lead to “capillary action” —  water can be pulled up vessels

• water ‘adheres’ to xylem vessels to allow transport in tall plants

• Water adheres to cellulose, a component of plant cell walls, greater than the cohesive forces, enabling the water to move upward from the roots to the leaves.

• polar molecules dissolve in water

• ions separate 

• ions become surrounded by water molecules

• e.g. salt.

• non-polar molecules will not dissolve in water

• non-polar regions of molecules orientate away from water

• polar regions orientate towards water

• e.g. phospholipids of cell membrane

• e.g. oils and fats.

Buoyancy: black-throated loon (Gavia arctica) can float on water due to water's upward buoyant force which counteracts the weight of the organism.

Viscosity: black-throated loons are hydrodynamic when diving for fish to reduce drag from the water. They "patter" (run) on water to take off, taking advantages of waters surface tension.

Thermal conductivity: feathers are oiled to prevent them getting wet. This retains an insulating layer of air which prevents birds from losing heat to the water.

Specific heat capacity (4.2 kJ/ kg): water has a high specific heat capacity, it does not change temperature providing a stable environment for the black-throated loon.

Buoyancy: black-throated loon must use it's wings to fly. The wings increase the surface area for the buoyant force of air to overcome weight of the bird.

Viscosity: black-throated loons are aerodynamic when flying to reduce drag from the air. As air is less viscous than water, the birds can fly and glide through the air with little resistance.

Thermal conductivity: down feathers under flight feathers trap an insulating layer to air to prevent heat loss to surrounding atmosphere. Air has less thermal conductivity than water.

Specific heat capacity (1.0 kJ/ kg): air has a low specific heat capacity, it can change dramatically in temperature and hence many birds are migratory, flying to warmer temperatures in winter months.

Buoyancy: aquatic animals such as the ringed seal (Pusa hispida) have low denisty blubber which increases their buoyancy in water.

Viscosity: seals are hydrodynamic when diving for fish to reduce drag from the water. They use their flippers to propel themselves through the water.

Thermal conductivity: thick layer of insulating blubber prevents heat loss to their environment. 

Specific heat capacity (4.2 kJ/ kg): water has a high specific heat capacity, it does not change temperature providing a stable environment for the black-throated loon.

Buoyancy: air is less buoyant that water and the blubber hinders the movement of the seal in land, making it slow and lumbering. 

Viscosity: air is less viscous than water but seals are not flight animals. The flippers can be used to drag the seal through snow and across land. 

Thermal conductivity: thick layer of insulating blubber prevents heat loss to their environment. 

Specific heat capacity (1.0 kJ/ kg): young seals stay in lairs which trap insulating air under snow and ice to prevent heat loss to the colder environmental air.