3: Water Flashcards
What are molecules with uneven share of electrons called?
Polar molecules
How is water a polar molecule?
Oxygen and hydrogen do not share electrons equally in a covalent bond (oxygen always has a much greater share of electrons)
How do hydrogen bonds form?
Positive and negative regions of polar molecules attract each other and form bonds (hydrogen bonds)
What are some features of hydrogen bonding
Relatively weak, break and reform between constantly moving water molecules, occur in high numbers
Why does water have an unusually high boiling point?
Hydrogen bonding between water molecules which require a lot of energy to overcome
Why is ice less dense than water?
As water is cooled the hydrogen bonds fix the positions of the polar molecules slightly further apart than the average distance in the liquid state. This produces a giant, rigid but open structure (a solid that is less dense than liquid water)
Why does water have cohesive properties?
It moves as one mass because water molecules are attracted to each other (cohesion). Water also has adhesive properties - water molecules are attracted to other materials
What allows water to have surface tension?
Water molecules are more strongly cohesive to one another than they are to air
How does water act as a solvent?
Water is a polar molecule. Many solutes are also polar (amino acids, proteins and nucleic acids) so water acts as a medium for chemical reactions
Why does water make a very efficient transport medium?
Cohesion between water molecules means that when water is transported, molecules stick together. Adhesion occurs between water molecules and other polar molecules and surfaces. Adhesion and cohesion result in water exhibiting capillary action (water can rise up a narrow tube against the force of gravity)
Why can water act as a coolant (help to buffer temperature changes during chemical reactions)?
Large amount of energy required to overcome hydrogen bonding
What does water being stable allow?
It provides a constant environment for organisms
What does ice floating allow?
Forms an insulating layer which allows aquatic organisms to survive
Why can some organisms inhabit the surface of water? Give an example.
Surface tension is strong enough to support small insects. Example = pond skaters
