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Thursday, October 11, 2012.docx

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York University
Natural Science
NATS 1840
Carol Bigwood

Science, Technology and the Environment (SC NATS 1840A) – Thursday, October 11, 2012 Readings 3.3, 3.5, 3.6, Appendix 3, 3.4, 3.7 Activity #1 ON KIT Matter, Chemical Reactions and Nuclear Reactions, Scientific Notation Ionic Bond Example: Carbon = C, needs 4 extra electrons Hydrogen = H, has 1 extra electron  Electrons are shared in a covalent bond H. .C. <= C has 4 dots around it and the two middle ones are connected, carbon would like it better if there are 4 h’s and have 8 electrons =>4CH (Methane)  Covalent bonds are weaker than ionic ones. Reactions: Processes in which nuclei, atoms, or molecules interact in a manner which changes how they are bound. Ingredients =====Reaction=== Products If products are more tightly bound overall compared to the ingredients, reaction is exothermic – energy is released (from the ingredients) in the reaction. If products are less tightly bound than the ingredients, reaction is endothermic – energy must be added to the ingredients for the reaction to occur. Chemical Reactions: Only atoms and molecules undergo chemical reactions. Only the electron clouds participate – nuclei are unaffected and remain intact. As a result, two important rules apply to chemical reactions: 1) Nuclei are conserved. So, the number of atoms of each element remains the same through a chemical change. 2) The total charge remains the same through the reaction. Example: Consider burning methane (natural gas) in air. Methane = CH 4 Burning (or combustion) means combining with oxygen (O 2) The combustion reaction is represented as CH 4 2O =2 CO + 22 O + 2nergy ^ ^ ^ Two oxyg
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