The periodic table is a chart that organizes all the elements according to their atomic numbers (# of protons) by groups—columns that have similar physical and chemical properties, and periods—rows which have the same number of energy levels.
We will use the “A” group elements to help the student get a basic understanding of how and why a chemical reaction occurs. I have found that having the student think of the symbols for the elements as letters of the alphabet to be very useful. I explain that just as there are rules for making words there are also rules for chemical reactions. There are a limited number of letters justs as there are a limited number of elements.
The electrons in the outer shell are responsible for chemical reactions. The atom wants to have a complete outer shell of eight electrons. This is accomplished by lending or borrowing 1 to 4 electrons. Let’s see how this is accomplished.
We will use the (+) for the tendency to give up electrons and the (-) sign for the tendency to borrow electrons. The roman numeral in front of the letter “A” indicates the number of electrons in the outer shell called valence electrons.
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IA = +
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IIA = ++
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IIIA = +++
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IVA = or
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- - - -
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VA = - - -
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VIA = - -
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VIIA = - -
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VIIIA = 0
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In order to have a chemical reaction, we need something to lend electrons and something to borrow electrons. The number of (+) must equal the number of (-) in a completed chemical reaction.
At this point we can combine some elements using this method.
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Li = +
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Cl = -
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rxn = LiCl
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H = +
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O = - -
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rxn = H O
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H = +
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2
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Al = +++
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O = - -
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rxn = Al O
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Al = +++
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O = - -
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2 3
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0 = - -
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Now that we have a basic understanding of what is happening during a chemical reaction, we will begin to investigate various problems in our environment.
