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.

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

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

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.

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:

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

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)

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

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

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!

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

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