1. Water.pdf

Title: Water Date: 04/09/2024 LI: To understand the properties and bonding of water molecules Starter: What is the chemical structure of water? What percentage of the Earth and of living organisms do you think is made up of water? Challenge: What type of...

Title: Water Date: 04/09/2024 LI: To understand the properties and bonding of water molecules Starter: What is the chemical structure of water? What percentage of the Earth and of living organisms do you think is made up of water? Challenge: What type of bonding is found in water molecules? Keywords: water, hydrogen bonds, condensation, hydrolysis  Title: Water LI: To understand the properties and bonding of water molecules Starter: - H2O - 60% of living things and 2/3´s of Earth Challenge: The bonding within water molecules is covalent bonds. The bonding between water molecules is hydrogen bonds. Keywords: water, hydrogen bonds, condensation, hydrolysis  Water: Guiding questions What chemical and physical properties of water make it essential for life? What are the challenges and opportunities of water as a habitat? Water has always been essential to life Draw a mindmap in your book and list as many reason as to why living organisms need water. Why do living things need water? Water has always been essential to life Water helps organisms regulate Many reactions in living their temperature organisms require water Why do living things need water? Because it is a solvent it can Water is a habitat for a lot of transport substances around the living organisms body Water is a solvent, so things dissolve in it The first living organisms and water Althought there are many hypotheses about how the first living organisms came to be, there is a general consensus that water was vital. Water was required for: 1.Effective interaction of the naturally formed molecules of life, allowing growth and copying of these molecules. 2.Formation of compartments, which allowed the development of internal chemistry different from the surrounding environment. The first living organisms and water For 4 billion years, water has been abundant on Earth. All living organisms which are formed of one or more cells are dependent on water. For example water is the solvent that: Notes: Makes up the cytoplasm Makes up the fluid inside all organelles Permits transport of substances in and out of cells Essential component of blood and other bodily fluids Provides habitats for many organisms in the form of rivers, oceans etc.  The chemical structure of water Water is formed of two hydrogen atoms and one oxygen atom which are covalently bonded. The chemical structure of water As you can see from the image, the electrons are not shared evenly between the Oxygen and the Hydrogen atoms. This is because the oxygen is more electronegative. What is meant by electronegativity? Recap from previous years: Electronegativity is the ability of an atom to attract a shared pair of electrons, this can be influenced by two factors: The number of protons in the nucleus: The positive protons in the nucleus attract the electrons in the shells. The number of orbital shells: The greater the number of shells between the outer electrons and the nucleus. Polarity of water Because Oxygen is more electronegative than Hydrogen, it attracts the shared pair of electrons greater. This uneven distribution results in the oxygen atom being slightly negative (δ-), whilst the hydrogen atoms are slight positive (δ+). This polarity of water gives it many of its unique Note: You may be used to seeing porperties. the Greek symbol Δ delta. However, we use the lowercase version of this symbol δ to show that the molecules are slightly positive or negative Polarity of water (key information/notes) Formed of 2 Hydrogen atoms and one Oxygen Oxygen is more electronegative than Hydrogen Water is a polar molecule, Oxygen is slightly negative and Hydrogen is slightly positive. The hydrogen atoms are 105 degrees apart. This is due to the repulsion between the electrons in the hydrogen atoms.  Bonding between water molecules (hydrogen bonds) Hydrogen bonds form when a slightly negatively charged part of a molecule comes close to a slightly positively charged hydrogen molecule in the same or another molecule. This bonds are weak, therefore, they are depicted with a dash lined, not a solid line (see image to the right). Tasks 1. Draw or describe what you know about the structure of hydrogen and oxygen atoms, the two elements that are combined in water. Remember that atoms do not have an overall charge. 2. Draw and describe the structure of water molecules including how the electrons are arranged. Explain the type of bonding within a water molecule. 3. Draw the hydrogen bonds between at least ten water molecules. Make sure you include the small delta (δ+ and δ–) symbols to show the polar covalent bonds that exist in water molecules. Answers 1. Answers 2. Answers 3. Key terms (copy in notes) Cohesion: A property of water in which water molecules are attracted to each other by hydrogen bonding, allowing the molecules to move together. Tension: A force that tends to stretch something. Adhesion: A property of water in which water molecules are attracted to surfaces such as walls of the cells, vessels or tubes. Cohesion and its consequences Because of the hydrogen bonds formed between water molecules. They are described as a highly cohesive molecule (attraction between the molecules). This can be clearly seen, if you put a few drops of water on a coin (see image below), the water forms a dome shape. Cohesion and its consequences The cohesive properties of water are very important in nature. Below are some examples: Movement of water in the xylem: Vascular plants use the cohesion of water to transport water up thin tubes called xylem, reaching to the top of the plant, sometimes tens of metres above ground Surface tension: Water striders (Gerris lacustris, also called pond skaters) live on the surface of relatively calm and unpolluted bodies of water Surface tension Have you ever wondered why it is so painful when you ´belly-flop´ into a swimming pool? This is because on the surface of water, there are relatively strong cohesive forces between water molecules which need to be over come. Examples of Surface tension It is this surface tension which allows organisms to live on the surface of still water. For an object to fall into the water the surface tension must be broken. Water tension in plants. Water is able to move in columns up plants due to cohesion. Water moves in a continuous column up small tubes in plants called ´xylem´. When water evaporates from the leaves in a process called transpiration, the water that evaporates is cohesively joined to the water in the xylem. This is in effect pulls water up the xylem to replace the water lost in the leaves. Adhesion of water Adhesion is attraction between water and other substances via hydrogen bonds. Note that water is not the only polar molecules in nature. Within the xylem cohesion and adhesion work together for a phenomena called capillary action. Cohesion allows water to move up the xylem in a continuous tube when water is being lost. However, when water is not being lost, the adhesion of water molecules to the walls of the xylem ensure that entire column of water does not drop down. Explain how adhesion and cohesion takes place in plants xylem cells.  Examples of capillary action in ACTION 1. Soil does not dry out at the surface as the roots of plants absorb water. This is because as the roots absorb water it is replaced at the surface by capillary action. 2. Plants also use capillary action to move water into cell walls. As water moves through the xylem, the cellulose fibres that compose the cell wall pull water into the spaces between them. When water evaporates from the surface of cells inside a leaf, capillary action draws out more water and prevents the cells from drying out. Water as a medium for metabolism Task: Suggest what the following terms mean: Hydrophobic Hydrophilic Water as a medium for metabolism Task: Answers Hydrophobic: These are molecules are usually non-polar (no charge) and cannot dissolve in water (e.g. water hating) Hydrophilic: These are molecules are usually polar and can dissolve in water (e.g. water loving) Examples of hydrophobic and Hydrophilic molecules in nature. Hydrophilic (Soluble): Hydrophobic (insoluble): Glucose Steroid hormones Ions Plasma membrane and nuclear membrane Amino acids Certain part of proteins Proteins e.g. enzymes Because steroids are This ensures they can be hydrophobic, they can pass transported easily. Making straight through the nuclear water an excellent transport membrane and interact with medium. DNA- Water as a medium for metabolism Water is incredibly important for many metabolic reactions. For examples the cytoplasm contains a huge number of dissolved substances. The cytoplasm is largely formed of water, and how these molecules interact with water can impact their actions. For example: The presence of water within enzymes can enable them to maintain their shape to be able to catalyse reactions. Water as a medium for transport In a large multicellular organism, such as a human, it is necessary to transport many compounds throughout the body. Each and every cell needs access to oxygen, glucose and minerals. At the same time, waste products have to be excreted. As a water-based liquid, blood takes care of the majority of these tasks Transport in animals Task: For each subatance, research its role in the human body. Physical properties of water In pairs, list as many properties of water as you can – try to include both chemical AND physical properties and list some roles of water in or by living organisms Check your list - properties Wide temperature range over which water is a liquid Ice is less dense than water (Bouyancy) High specific heat capacity High latent heat of evaporation Polar molecule- slightly positive and negative Reactant Many hydrogen bonds Transparent High specific capacity Water has a high specific capacity. Think back to your chemistry Gr.10 class, what does this mean? Because of the hydrogen bonds between water molecules, it takes a lot of energy to raise the temperature of water, as the H-bonds can absorb a lot of the energy. Why do you think this makes water a good habitat for animals? This means water doesn't experience rapid changes in temperature. Tip: SHC is the amount of energy required to increase the temperature of 1kg of a substance by 10C. High latent heat of evaporation How does evaporation of water help to cool us down? Sweat evaporates from the surface of our skin and helps to cool us down. Hydrogen bonds require energy for the bonds to be broken. For sweat to evaporate these bonds must be broken. Why does this make water the perfect molecule to cool us down? A lot of energy (heat) is required from the surface of our skin to break this bonds. Therefore, it cools the organism very quickly Tip: Latent heat is the energy required to change a substance from one state to another e.g. liquid to gas  Lower density when solid (Buoyancy) Why does ice float on liquid water? The ice is less dense than the liquid water. Look at the image below. Why is the fish below the ice not frozen (dead)? When water freezes it becomes less dense and floats. This insulates the water below and stops it from freezing. This is why all the fishes don’t die when a lake freezes over Tip: Density refers to how closely the particles are packed together e.g. if if substance has a high density it means more molecules are packed into the same space, thus making it heavier Thermal conductivity Thermal conductivity is the ability of a substance to transfer heat when there is a temperature difference. Water has a high thermal conductivity compared with other liquids (except liquid metals). Air has a much lower thermal conductivity than water. This means that organisms (warm blooded) will lose heat quicker in water compared to the air. Therefore, they will need mechanisms to overcome this such as blubber.  Good solvent Why do you think both positive and negative substances can dissolve in water? Draw a diagram to explain your answer. Extension: Fish in a pond need ions and minerals such as nitrates (NO3-) and Magnesium (Mg2+) to survive. Explain how living in water can help them obtain these minerals Exam Tip: A polar molecule is has a Tip: Because water is such a good solvent most slightly positive and a slightly biological reactions happen in water. The negative side cytoplasm and blood plasma are mainly formed of water Physical properties of water: Research task Choose a local species of animal or one in which you are particularly interested. Read about the habitat and life cycle of the species and pay special attention to its relationship with water. Research and outline the adaptations that the species has in relation to at least three of the following properties of water: cohesion, adhesion, surface tension, solvent properties, buoyancy, viscosity, thermal conductivity and specific heat capacity. Be sure to cite your sources. Present your ideas to your class. Example Example Origin of water on Earth When the planet Earth first formed, between four and five billion years ago, it was far too hot to have liquid water on its surface. Scientific evidence suggests that water was delivered to Earth through many collisions with water-rich asteroids (image to the right), also known as comets. Reasons for retention of water on Earth As the Earth began to cool, water was able to condense and the force of Earth’s gravity helped to retain water on the Earth’s surface. The Earth has remained at a moderate temperature, with water neither boiling away nor frozen solid. The presence of liquid water as a solvent and medium for metabolism is considered necessary for life as we know it to exist.  Extraplanetary Origin of Water Where Did Earth's Water Come From? This video sponsored by Tab for a Cause: http://www.tabforacause.org?r=3 Read the linked article Please support MinuteEarth on Patreon: https://goo.gl/ZVgLQZ 1. Explain why water was not And subscribe! http://goo.gl/EpIDGd Earth didn't have water when it formed, but it does now! How did it get wet? Created by Henry Reich Animation: Ever Salazar Production and Writing Team: Alex Reich, Peter Reich, Emily Elert present on Earth when the Music: Nathaniel Schroeder: http://www.soundcloud.com/drschroeder Want to add captions to MinuteEarth videos? - minuteearth.subtitl.us planet formed. MinuteEarth is available as a free iTunes podcast! - https://goo.gl/sfwS6n 2. Explain how the Earth gained Facebook - http://facebook.com/minuteearth Twitter - http://twitter.com/MinuteEarth its oceans MinuteEarth provides an energetic and entertaining view of trends in earth's environment -- in just a few minutes! References 3. Explain why the Earth does not lose its water. Campbell, I. H., O'Neill, H. S. C. (2012). Evidence against a chondritic Earth.Nature, 483(7391), 553-558. Drake, M. J. (2005). Origin of water in the terrestrial planets. Meteoritics Planetary Science, 40(4), 519-527. Greenwood, J. P., Itoh, S., Sakamoto, N., Warren, P., Taylor, L., Yurimoto, H. (2011). Hydrogen isotope ratios in lunar rocks indicate delivery of cometary water to the Moon. Nature Geoscience, 4(2), 79-82. Hauri, E. H. (2013). Planetary science: Traces of ancient lunar water. Nature Geoscience, 6(3), 159-160. Marty, B. (2012). The origins and concentrations of water, carbon, nitrogen and noble gases on Earth. Earth and Planetary Science Letters, 313, 56-66. Pepin, R. O. (2006). Atmospheres on the terrestrial planets: Clues to origin and evolution. Earth and Planetary Science Letters, 252(1), 1-14. Robert, F. (2001). The origin of water on Earth. Science, 293(5532), 1056-1058. Robert, F. (2011). Planetary science: A distinct source for lunar water?. Nature Geoscience, 4(2), 74-75. Saal, A. E., Hauri, E. H., Van Orman, J. A., Rutherford, M. J. (2013). Hydrogen Isotopes in Lunar Volcanic Glasses and Melt Inclusions Reveal a Carbonaceous Chondrite Heritage. Science, 340(6138), 1317-1320. 1. Explain why water was not present on Earth when the planet formed. Earth and the other rocky planets of the inner solar system formed by the clumping together of solid particles. Water, in the form of ice, was not present, as the temperatures were too high for water to exist as a solid (ice). Any gaseous water would have been moved away by the solar winds.  2. Explain how the Earth gained its oceans Water formed solid particles in the outer solar system as a result of low temperatures, due to the distance from the sun. The ice formed objects such as comets and asteroids. Earth's water probably arrived from the asteroids (carbonaceous chondrites) , which have similar ratios of heavy hydrogen atoms as Earth’s water. The water probably arrived during the Late Heavy Bombardment, four billion years ago. 3. Explain why the Earth does not lose its water. Planet Earth’s large mass creates enough gravity to retain the liquid water and water vapor on the planet. Earth’s much smaller moon has less gravity and cannot retain water vapor. The Earth is in a habitable zone of the solar system where water can exist as liquid water. The temperature of Earth is suitable for the water cycle, as water vapor condenses to liquid water, and falls back to the Earth as precipitation.  The Goldilocks Zone Goldilocks | Known Universe Which planets in our galaxy are "just right" for supporting human life? ➡ Subscribe: http://bit.ly/NatGeoSubscribe Read the linked article. About National Geographic: National Geographic is the world's premium destination for science, exploration, and adventure. Through their world-class scientists, photographers, journalists, and filmmakers, Nat Geo gets you closer to the stories that matter and past the edge of what's possible. Get More National Geographic: Scientists believe that liquid Official Site: http://bit.ly/NatGeoOfficialSite Facebook: http://bit.ly/FBNatGeo Twitter: http://bit.ly/NatGeoTwitter Instagram: http://bit.ly/NatGeoInsta Goldilocks | Known Universe https://youtu.be/u2OlT9bECqg water is required for life to exist National Geographic https://www.youtube.com/natgeo on planets. Scientists are currently searching for exoplanets with liquid water which may support extraterrestrial life. Planets are in the habitable zone (Goldilocks zone), when their orbit around their star allows liquid water. The planet is not too hot and not too cold for liquid water to exist. The search for extraterrestrial life Most astrobiologists believe extraterrestrial life will be found only in the presence of liquid water on other planets or natural satellites. The habitable zone, or Goldilocks zone, refers to the orbital distance from a star that will result in liquid water. The planet Earth is in the Goldilocks zone because its distance from its start (the Sun) is neither too hot nor too cold to prevent liquid water – it is just the right distance. A planet which is thought to have once had large amounts of water is Mars, it is within the ´Goldilocks zone´. Images of the surface indicate their could have been water (see next slide). Evidence of past liquid water on the surface of Mars. Key summary for students Water is the substance in which cells first developed and remains necessary for the processes of life to occur. The difference in electronegativity between hydrogen and oxygen leads to polar covalent bonds within water molecules and hydrogen bonds between them. Water molecules are cohesive, which leads to surface tension. Some animals, like water striders, can live on the surface of water. Water can dissolve many substances including substrates, such as sugar, and enzymes, such as amylase, needed in metabolism. The solvent properties also allow organisms to make water-based solutions to transport dissolved substances. Water is adhesive to polar and charged substances which are known as hydrophilic. Key summary for students Water is buoyant and viscous compared with air. Water has high thermal conductivity and high specific heat capacity compared with air. The ringed seal and black-throated loon have hydrodynamic shapes for swimming. The ringed seal has blubber for insulation, while the loon uses a layer of dry air and downy feathers. Most of the water on Earth is believed to have been delivered by asteroids. The moderate temperature of the Earth keeps water liquid and gravity allows water to be retained. The concept of the ‘Goldilocks zone’, or habitable zone, is the orbital area around a sun where a planet or natural satellite might have liquid water. Complete questions