1. WATER On earth, water is the substance that makes life possible as we know it. Many of water’s important biological functions directly stem from its chemical structure.

2. Structure of Water -two hydrogen atoms joined to an oxygen atom, each hydrogen atom is joined by a single covalent bond -the shape and bond angle allow for a charge separation, or an unequal sharing of electrons in the covalent bonds

3. Draw the Structure of Water using Bohr-Rutherford Diagrams to show the Covalent Bonding between atoms:

4. WHY DOES HYDROGEN BONDING OCCUR? -oxygen has more protons in its nucleus than hydrogen so the electrons in the covalent bonds spend more time closer to the oxygen atom -this means that the oxygen is SLIGHTLY negative, and the Hydrogen in SLIGHTLY positive -the atoms of a water molecule are not arranged in a straight line, rather they are at right angles to each other -Thus we say that water is a POLAR molecule: a molecule that has opposite charges on opposite ends.

5. Hydrogen Bonding -not really a "bond"* at all, but rather a weak electrostatic attractionbond -each water molecule can form hydrogen bonds with a maximum of four neighbours Draw Hydrogen Bonding between water molecules using Bohr-Rutherford Diagrams:

6. Hydrogen Bonding can also occur between other molecules that are polar.

7. HYDROGEN BONDING GIVES WATER 4 UNIQUE PROPERTIES: The Properties of Water: 1. Water demonstrates Capillarity Capillarity: water molecules moving through narrow tubes against the force of gravity -organisms depend on the cohesion of water molecules -water molecules ‘stick’ together as result of hydrogen bonding -when water is in its liquid form, its hydrogen bonds are very weak: they re-form and break with great frequency -at any instant, most water molecules are bonded with their neighbours giving water more structure than other liquids Cohesion: the attractive force between particles of the same kind Adhesion: the attractive force between different kinds of particles -water is also attracted to particles of different kinds (example: to the walls of plant cells so water can get up from the roots to the leaves)

8. 2. Water has a High Surface Tension Surface Tension: the measure of how difficult it is to stretch or break the surface of a liquid -water has a greater surface tension than most other liquids -where air and the surface of the water meet, water molecules are bonded to each other and the surface below -this makes the water behave as though it was coated with an invisible film (ie) allows us to skip rocks -allows organisms such as water striders to survive on the water

9. 3. Water has a High Specific Heat Capacity Specific Heat Capacity: the amount of heat that must be absorbed or lost for one gram of that substance to change its temperature by 1 o Celsius -water contributes to Earth’s habitability by moderating temperatures -water stabilizes air temperatures by absorbing heat from air that is warmer and releasing the stored heat to air that is cooler (lake effect) -changes temperature gradually when heated/cooled so offers cells protection/stable internal environment

10. 4. Water is Less Dense as a Solid than a Liquid -water is less dense as a solid than a liquid- expands as it becomes a solid -prevents deep bodies of water from freezing solid from the bottom up, oceans and lakes don’t freeze because ice floats!

11. 5. Water is the Solvent of Life -water is a versatile solvent due to its polarity -water is extremely effective in dissolving other substances

12. Summary of Important Concepts about Water: 1.Structure -unequal sharing of electrons in covalent bonds= POLAR MOLECULE 2.Function Because water is a POLAR MOLECULE: a)It has capillarity b)It has a High Surface Tension c)It has a High Specific Heat Capacity d)It is less dense as a solid than a liquid e)It is the universal solvent of life