Chapter 2 Atoms Molecules 1 Elements a substance that cannot be broken down to other substances by chemical reactions Essential Elements Oxygen O Carbon C Hydrogen H Nitrogen N Calcium Ca Phosphorus P Potassium K Sulfur S Sodium Na Chlorine Cl and Magnesium Mg Trace Element only needed in tiny amounts Boron B Cobalt Co Copper Cu Fluorine F Iodine I Iron Fe Silicon Si and Zinc Zn 2 Compound a molecule that consist of two or more elements combined in a fixed ratio ex NaCl and H2O 3 Atom the smallest unit of matter that still retains the chemical and physical properties of an element 4 Chemical Bonds attractions that hold molecules together Covalent Bonds strong bonds shared electrons Nonpolar Covalent Bonds electrons will be shared equally Polar Covalent Bonds electrons will not be shared equally Ionic Bonds strong bond transferred electrons when a cation positively charged ion and an anion negatively charged ion attract to each other result called ionic compounds or salts Hydrogen Bonds weak bond important in DNA and proteins when a hydrogen atom covalently bonds to an electronegative atom 5 Chemical Reactions making and breaking chemical bonds reactants make a change into a product reactants products 6 Energy Levels 1st shell 2 2nd shell 8 Chapter 3 Water Water contributes to the fitness of the environment to support life Cells are 70 to 95 water Water s various properties are the results of its structure and molecular interaction 1 Water is a polar molecule It has opposite charges on opposite sides to allow maximum bonding Water molecules are held together by hydrogen bonds 2 Water is cohesive Water molecules stick to each other Water has more structure than other liquids because so many of the water molecules are hydrogen bonded at one time Cohesion helps water molecules travel up plant stems 3 Surface Tension The measure of how difficult it is to break the surface of a liquid Water has high surface tension and bonding 4 Adhesion When water molecules cling to hydrophilic substances like glass Water molecules do not cling to hydrophobic substances like wax Adhesion aids in water movement in plants and animal tissues 5 Water stabilizes temperature It resists temperature changes when it absorbs or releases heat The oceans are huge heat sinks that help to regulate the earth s temperature 6 Water is a versatile solvent the dissolved substances are solutes Hydrophilic substances are water soluble Hydrophobic substances are NOT water soluble This will be very important with the structure and function of the cell membrane 7 Acids Bases and pH pH is a measure of H ions or OH ions in a solution due to transfer between water molecules If H OH it is a neutral solution If H OH it is an acidic solution If H OH it is a basic solution 8 Buffers are substances that help to stabilize pH levels in living things Body fluids need to have a pH of 6 to 8 Buffers helps to maintain that narrow pH range A buffer can accept H ions when they are in excess or donate H ions when they have been depleted Common buffer bicarbonates found in Tums pepto bismol and buffered aspirin
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