Properties of Water PDF

TOPIC 2 UNIT 1.1 FOUNDATIONAL CHEMISTRY PROPERTIES OF WATER Learning Targets: Describe the molecular structure of water, including the arrangement of hydrogen and oxygen atoms and the nature of the covalent bonds. Define and distinguish between cohesion and adhesion in water molecules....

TOPIC 2 UNIT 1.1 FOUNDATIONAL CHEMISTRY PROPERTIES OF WATER Learning Targets: Describe the molecular structure of water, including the arrangement of hydrogen and oxygen atoms and the nature of the covalent bonds. Define and distinguish between cohesion and adhesion in water molecules. Describe water’s ability to dissolve a wide range of substances, identifying it as the "universal solvent" due to its polarity. Explain water’s high specific heat, heat of vaporization, and how these properties stabilize temperatures in living organisms and environments. www.ens.sch.ae  Water Water = 1 atom of oxygen and 2 atoms of hydrogen held together by covalent bonds (H2O) Water is a Polar Molecule → unequal distribution of charges One side is more positive One side is more negative When water molecules are close, their opposite sides are attracted to each other because of polarity This attraction between water molecules is responsible for most of the properties of water. Hydrogen Bonding A hydrogen bond is the attraction between the positively charged hydrogen atom of one molecule and the negatively charged atom (N, O, or F) of another molecule. ○ A single hydrogen bond is easily broken, but many can be collectively strong.  Covalent bonds internally hold a water molecule together – Different water molecules are held together externally by very weak hydrogen bonds Covalent Hydrogen Properties of Water: Cohesion & Adhesion Hydrogen bonding gives water many unique properties that are essential to life on Earth. Water molecules are cohesive and adhesive: ○ Cohesion is the ability of water molecules to “cling” to each other due to hydrogen bonding. Ex: Water forming droplets ○ Adhesion is the ability of water molecules to “cling” to other polar surfaces due to hydrogen bonding. Ex: Water drops sticking to glass Properties of Water: Cohesion & Adhesion Cohesion and adhesion create capillary action: water’s ability to “climb” narrow spaces. Biological Example: Cohesion and adhesion allows water to be transported up plants against gravity, through microscopic “tunnels” and pores in plant tissue. Water “sticks” to itself Properties of Water: Surface Tension Cohesion also causes water to have a high surface tension. Surface tension is the force created from the molecules at the surface of a liquid being attracted to the molecules below the surface. Surface tension causes water to form droplets, so that it can minimize surface area as much as possible Surface tension also creates a force at the surface of water that is resistant to breaking when objects are carefully placed on it. ○ Ex: Some insects can “walk” on water. Properties of Water: Specific Heat Capacity Water has a high specific heat capacity: ○ Water absorbs lots of thermal energy without a great change in temperature. ○ Biological Examples: Organisms are made of mostly water, which allows them to maintain normal internal temperatures and protects them from rapid temperature change. Coastal habitats have a more stable climate with less fluctuating temperatures, because the nearby ocean absorbs a lot of heat. Properties of Water: Specific Heat Capacity Properties of Water: Heat of Vaporization Water has a high heat of vaporization: ○ Liquid water has to absorb a lot of thermal energy to break its hydrogen bonds so that it can evaporate into water vapor. ○ Biological Example: Evaporative cooling. When animals sweat or get splashed, their body heat is used to evaporate the water, taking away heat from their bodies. Properties of Water: Density of Ice Water expands when it freezes : ○ Due to its hydrogen bonds, water expands when it freezes, causing it to be less dense as a solid. ○ Biological Example: When bodies of water freeze, the ice floats, insulating the water beneath, allowing life to still exist. Prevents lakes from completing freezing. Properties of Water: Universal Solvent Water is the “universal solvent”: ○ A solution is made up of a solute (the substance being dissolved) and a solvent (the substance it’s dissolved in). ○ Because of its polarity, water is able to dissolve many different substances. ○ Biological Example: Blood and cells are mainly composed of water, which allows many essential substances to dissolve and be transported throughout the body (such as proteins, nutrients, minerals, and waste). Check your understanding Explain how cohesion and adhesion are being shown in the picture to the right. Check your understanding How does water travel up a tree from its roots in the soil to the leaves at the top? Check your understanding A paperclip sinks when placed in a cup of water. However, if it is rested very gently and carefully on the surface of the water, it will float. How is this possible? Check your understanding Elephants spray water on themselves to cool down their bodies. What property of water makes this possible? Check your understanding Lysozymes are large protein molecules found in tears and saliva that kill bacteria. Would you predict that a lysozyme molecule is polar or nonpolar? Why?