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
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.
Processes in which nuclei, atoms, or molecules interact in a manner which changes how they are
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.
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
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
The combustion reaction is represented as
CH 4 2O =2 CO + 22 O + 2nergy
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