General Chemistry 2 PDF

Lesson 1.4 The Structure and Unique Properties of Water General Chemistry 2 1/2 Science, Technology, Engineering, and Mathematics Have you ever thought about why researchers keep looking for traces of water on other planets?...

Lesson 1.4 The Structure and Unique Properties of Water General Chemistry 2 1/2 Science, Technology, Engineering, and Mathematics Have you ever thought about why researchers keep looking for traces of water on other planets? 2 This is mainly because water is essential to life. All life on earth depends on water. 3 We, as humans, use water for drinking, cooking, cleaning and making other substances. 4 If a planet has liquid water in it, then there is a chance that life, similar to Earth, may exist. 5 5  In this lesson, you will learn about the unique properties of water that make it suitable for life. 6 What are unique and important properties of water? 7 Learning Competency At the end of the lesson, you should be able to do the following: Explain the properties of water with its molecular structure and intermolecular forces (STEM_GC11IMF-IIIa-c-103). 8  Learning Objectives At the end of the lesson, you should be able to do the following: Describe the structure of water. Identify the interaction of water molecules. Relate the intermolecular forces on the properties of water. 9 What is the molecular shape of water? 10 The Structure of Water Water is represented by the chemical formula H2O. Lewis structure of water 11  The Structure of Water There are 4 electron domains around the central atom, O. Lewis structure of water 12  The Structure of Water The electron domain geometry of water is tetrahedral. Lewis structure of water 13 The Structure of Water Since there are two lone pairs present, the molecular geometry becomes bent. Lewis structure of water 14  The Structure of Water Since oxygen is more electronegative than hydrogen, then the dipole moment moves towards the oxygen atom. dipole moment of water 15  The Structure of Water The dipole moments do not cancel out. This means that the water molecule is polar. dipole moment of water 16 Remember Water has 4 electron domains around the central atom (O). It has two single bonds and two lone pairs. Its electron domain geometry is tetrahedral and its molecular geometry is bent. 17 What intermolecular forces are present in water? 18  IMFAs Present in Water Water is an electrically neutral molecule. It exhibits the following intermolecular forces: London dispersion forces; dipole-dipole interactions; and hydrogen bonding 19 Much of the unique properties of water are owed to the hydrogen bonding capacity of water. 20 H-bonding in Water 21 What are the unique properties of water? 22  Properties of Water Physical Properties of Water Property Values specific heat capacity (liquid water) 4.18 J/g · ºC specific heat capacity (water vapor) 2.11 J/g · ºC specific heat capacity (ice) 2.00 J/g · ºC melting point 0 ºC boiling point 100 ºC 23  Properties of Water Water has the highest boiling point due to H-bonds. 24  Properties of Water This makes it more difficult to break the interactions between particles. 25  Properties of Water Water as a Universal Solvent Water is known to be the universal solvent due to its capacity to dissolve a wide variety of substances. Its ability to dissolve ionic solids stems from the polarity of the water molecule. 26 When ionic compounds are dissolved in water. The ions break apart and each ion will be surrounded by water molecules, forming hydration sphere. 27  Properties of Water Water can dissolve ionic compounds through ion-dipole interactions. 28  Properties of Water Water can dissolve polar compounds through dipole-dipole interactions. 29 Amphiphatic molecules contain a polar and nonpolar regions. Fatty acids, such as palmitic acid, contain a long hydrophobic tail and a hydrophilic head. 30 When placed in water it forms a micelle, which is an assembly of fatty acids, wherein the hydrophobic tails are hidden inside the structure and the hydrophilic heads are exposed. 31  Properties of Water Heat Capacity Heat capacity is the amount of heat required to raise the temperature of a substance by 1 ºC. Specific heat capacity refers to the amount of heat required to raise the temperature of one gram of a substance by 1 ºC. For liquid water, the specific heat capacity is 4.18 (J/g ✕ ºC). 32  Properties of Water Heat Capacity Specific heat, c Specific heat, c Substance Substance (J/g ✕ ºC) (J/g ✕ ºC) liquid water 4.18 magnesium 1.024 water vapor 2.11 aluminum 0.903 ice 2.00 iron 0.449 dry air 1.01 zinc 0.389 granite 0.79 copper 0.385 33  Properties of Water Heat Capacity Remember that from the kinetic molecular theory, temperature is defined as the measure of the average kinetic energy of the particles. When the particles move faster, this translates to a higher temperature. The hydrogen bonds are able to absorb the energy in the form of heat. 34 Remember Heat capacity is an extensive property while specific heat is an intensive property. 35  Properties of Water Phases of Water Water, like all matter, can exist as a solid (ice), liquid (water), or gas (steam). From the kinetic molecular theory, solids typically have a more compact arrangement of particles than liquids and gases. However, this is not true for water. 36 When liquid water solidifies to ice, it arranges itself based on the hydrogen bonding requirements. 37 When a hydrogen bond is formed the hydrogen donor-hydrogen acceptor-hydrogen atom bond should be 180 degrees. 38 What happens to the volume of water when it melts? 39  Check Your Understanding Identify the terms described in each of the following items. 1. It is the type of covalent compound that applies to water. 2. It is the molecular geometry of water. 3. It is the amount of heat needed to increase the temperature of a gram of a substance by one degree Celsius. 40  Let’s Sum It Up! Water is a polar molecule with a bent geometry. The intermolecular forces present in water are: ○ London dispersion forces ○ dipole-dipole interactions ○ hydrogen bonding Water is the universal solvent since it can dissolve a wide variety of solutes. 41  Let’s Sum It Up! The water’s high boiling point and heat capacity are both due to the strong hydrogen bonds present in water molecules. Liquid water is more dense than ice due to the geometrical and spatial restrictions of the hydrogen bonds. 42 Challenge Yourself How can you relate the properties of water to its important role in maintaining life. 43 Bibliography Brown T.L. et al. 2012. Chemistry: The Central Science. Pearson Prentice Hall.Brown. Chemistry: The Central Science. Prentice-Hall, 2005. Bettelheim, Frederick A., et al. 2015. Introduction to General, Organic and Biochemistry. Boston: Cengage Learning. Ebbing, Darrell and Steven Gammon. 2016. General Chemistry. Boston: Cengage Learning. Moore, John W, and Conrad L. Stanitski. 2015. Chemistry: The Molecular Science, 5th ed. USA: Cengage Learning. Petrucci, Ralph H. General Chemistry: Principles and Modern Applications. Toronto, Ont.: Pearson Canada, 2011. Print. 44