Chapt 5-Seawater(1).doc - OCE-2001 Bolton 1 Chapter 5 –...

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OCE-2001 Bolton 1 Chapter 5 – Seawater The Molecular Structure of Water - atoms make up molecules. Atoms have a nucleus, containing protons (+) neutrons (neutral) Electrons (-) orbit the nucleus. o Atoms bond with other atoms to fill outer shell o 1st shell = 2 electrons; 2nd and 3rd shells = 8 electrons Chemical bonds hold molecules together 1. Covalent bond – atoms share electrons ( strongest ) – electrons shared 2. Ionic bonds – one atom gives up an electron to another atom; resulting in two charged particles that attract each other (weaker than covalent bonding). One gains an electron and becomes negative, the other loses an electron and becomes positive. 3. Hydrogen bonds – attraction of polar molecules (weakest). Water Molecules H 2 O –2 hydrogen and 1 oxygen molecule bonded together covalently (sharing electrons) Both H atoms on same side of O atom Polar molecules – one part of the molecule is oppositely charged from the other part of the molecule like a bar magnet (+ and – ends) o Polarity of covalent bonds - Electrons not equally distributed in molecule Water is a dipolar molecule (two polar covalent bonds) - both ends charged, like a battery or bar magnet O - Oxygen strongly attracts electrons - slightly negative H – Hydrogen slightly positive Allows formation of Hydrogen (H)-bonding between water molecules - Water molecules link together with hydrogen bonds through attraction between + and – ends of water molecules - to each other or to other ions like salts Hydrogen bonding gives water interesting properties H-bonds absorb red light and reflect blue light –gives water the blue color High solubility of chemical compounds Solid, liquid, gas at Earth’s surface High surface tension Unusual density Unusual thermal properties
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OCE-2001 Bolton 2 Unique properties of water Universal solvent - facilitates chemical reactions both outside and within living systems. Because of hydrogen bonding, water easily separates ionic bonds. Example: NaCl à Na + and Cl - Cohesion - water molecules are “sticky”. Due to hydrogen bonding, water clings to itself Surface tension – surface layer of a liquid that causes that layer to behave as an elastic sheet, allowing animals like the water strider to walk on water. Capillary action – the process of water moving up a narrow tube against the force of gravity because water adheres to the sides of the tube. Surface tension straightens the surface making the surface rise. More water is pulled up through cohesion. Three states of Matter Solid – liquid – gas Matter changes state due to adding or subtracting heat The state of matter is based mainly on temperature. Heat - kinetic energy – energy of movement Heat is energy of moving molecules Calorie - amount of heat needed to raise the temp of 1 g of water by 1 o C Temperature is measurement of average kinetic energy Thermal properties of H 2 O high boiling point high freezing point Most H 2
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