Lesson 6 - Water Flashcards
Definition of polar
Polar molecules have regions of negativity and regions of positivity.
Explanation of polar
The atom with a greater share of negative electrons will be slightly negative, compared with the other atom in the bond which is positive.
How come electrons are not shared equally in water?
Oxygen has a much greater share of electrons in the O-H bond. So hydroxyl molecules are slightly polar.
Water contains two hydroxyl bonds.
How do hydrogen bonds occur in water?
Polar molecules interact with each other, as positive and negative regions attract each other and form bonds. These are called hydrogen bonds.
Hydrogen bonds are weak:
Break and reform between constantly moving water molecules
How come hydrogen bonds are effective?
Occur in high numbers
Characteristics of water:
- high boiling point
- Cohesive
- Adhesive
Compare boiling point of water to other small molecules?
Carbon dioxide is a gas at room temperature, but water is a liquid
Freezing of water:
Water becomes less dense as a solid (unlike most molecules). This is because hydrogen bonds are formed.
As water is cooled below 4 degrees, the hydrogen bonds fix the positions of the water molecules slightly further apart than the average distance in liquid state.
Structure of ice:
Giant, rigid, but open structure. Every oxygen atom is at the centre of a tetrahedral arrangement of hydrogen atoms.
Result of low density of ice:
It floats
Cohesion definition:
Molecules are attracted to each other.
Result of water’s cohesive nature:
Water moves as one mass.
- Plants are able to draw water up their roots
- Can drink through a straw
Adhesive definition:
Molecules are attracted to other materials.
Result of water being adhesive:
Can wash hands and hands become wet, water doesn’t run off.
Why does water have a ‘skin’ surface tension?
Water molecules are more attracted to each other than the air.
Results of water acting as a solvent:
- Cytosol of prokaryotes and eukaryotes are mostly water
- Water acts as a medium for chemical reactions and helps to transport dissolved compounds into and out of cells.
Other polar molecules:
- Amino acids
- Proteins
- Nucleic Acids
What does adhesion of water occur between?
- Other water molecules
- Other polar molecules
- Surfaces
Results of adhesion and cohesion:
Capillary action
What is capillary action?
This is the process by which water can rise up a narrow tube against the force of gravity.
How is water an effective transport medium:
Cohesion between water molecules means that water is transported through the body and molecules will stick together.
Effect of water as a coolant:
Buffer temperature changes during chemical reactions in prokaryotic and eukaryotic cells because of the large amounts of energy required to overcome hydrogen bonds.
Why is it important for water to maintain temperatures in cellular environments?
Enzymes are only active in a small range of temperatures
Results of ice floating:
Forms an insulating layer above the water below.
Why is the insulating layer of ice important?
Aquatic organisms would not be able to survive freezing temperatures if their environment froze solid.
How is surface tension good for some insects?
The surface tension is strong enough to support small insects such as pond skaters.
How does water provide a constant environment?
It does not change temperature easily.
