3.2 - Water Flashcards
How does a molecule become polar
When atoms share electrons through a covalent bond, the electrons are not shared equally. The atom with the greater share of electrons will have a delta negative charge whilst the other has a delta positive charge. These are regions of negativity and positivity.
How do polar molecules interact
Positive and negative regions of molecule attract each other and form bonds (in H20 they form hydrogen bonds)
Describe hydrogen bonds
Weak interactions
Occur in high numbers
Gives water unique characteristics that are essential for life on this planet.
Boiling point of water
Unusually high boiling point for a small molecule that is lighter than some gases.
Liquid at room temperature due to high amount of energy required to break hydrogen bonds between water molecules
Water’s density as a solid
Less dense as a solid due to hydrogen bonds.
As cooled below 4* hydrogen bonds fix polar molecules slightly further apart than average distance in liquid state.
Giant, rigid but open structure.
Oxygen at centre of tetrahedral structure of H atoms
Definition of cohesive (in terms of water)
Moves as one mass as particles are attracted to each other.
How is cohesion in water beneficial
Plants can draw up water, through their roots.
Drink water through a straw.
More cohesive to each other than they are to air so water has skin of surface tension.
Definition of adhesive (terms of water)
Water molecules are attracted to other materials
Benefits of adhesive characteristic of water
When you wash your hands, your hands become wet. Water doesn’t just run off.
Benefits of water being polar
Acts as a solvent. Polar solutes in an organism can be dissolved (e.g. in eukaryotic cells water acts as a medium for chemical reactions and helps transport dissolved compounds into and out of cells)
Benefits of water being cohesive and adhesive
Efficient transport medium. Exhibits capillary action - water rises up narrow tube against the force of gravity.
How does water help temperature
Acts a coolant
Buffers temperature changes during chemical reactions in prokaryotic and eukaryotic cells due to large amount of energy required to break H bonds.
Important as enzymes often only active in narrow temperature range
How feature of water help underwater creatures
Doesn’t change temperature or become gas easily - stable, constant environment
Ice floats- forms on surface of ponds and lakes. Provides an insulating layer. Aquatic organisms would not be able to survive if their habitat froze.
Surface tension - strong enough to support insects such as pond skaters
