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 attraction -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 CapillarityCapillarity: 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 liquidsCohesion: the attractive force between particles of the same kindAdhesion: 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 TensionSurface 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 CapacitySpecific Heat Capacity: the amount of heat that must be absorbed or lost for one gram of that substance to change its temperature by 1o 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.FunctionBecause water is a POLAR MOLECULE:a)It has capillarityb)It has a High Surface Tensionc)It has a High Specific Heat Capacityd)It is less dense as a solid than a liquide)It is the universal solvent of life