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This fanciful image of an atom schematically shows the general structure --- a central nucleus surrounded by a cloud of electrons.Jupiterimages/Photos.com/Getty Images
List the atomic numbers of the elements. This is the number of protons in the nucleus of the element, which is identical to the number of electrons in the cloud surrounding the nucleus. - 2). Use the quantum mechanical rules to determine the number of valence electrons. The number of valence electrons is responsible for nearly all the element's chemical behavior and that is the underlying organizational scheme for the periodic table. The electrons needed to balance out the protons of the nucleus will find the lowest energy permissible state: filling "shells" according to the complex rules of quantum mechanics.
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Vertical columns in the periodic table represent atoms with identical numbers of valence electrons, leading to similar chemical properties.Jupiterimages/Photos.com/Getty Images
Set up the two outer columns of a table. The left column will represent atoms that have one valence electron --- atoms that are very reactive, because that one electron is easily available to link with other atoms. The right column represents atoms that have a full valence shell, with no electrons available for bonding. - 4). Fill in the first row of the table. The left column will have an atomic number of one and one valence electron. The first electron level is full when it has two electrons, so the next entry in the first row goes into the "full shell" column on the right.
- 5). Fill in the second row of the table. This represents the set of electrons that are just a bit further away from the nucleus than the first row. This time, the level is full with 8 electrons. So the left-most column will have atomic number 3, with one valence electron, right under element 1. The right-most column will have atomic number 10. The intervening spaces, from 4 to 9, fill in the space in between.
- 6). Fill in the third row of the table. The situation starts to get a little more complex now, but the rule for this row is just the same as the second row, so it starts at element 11, with one valence electron, and ends at element 18, with a full shell.
- 7). Fill in the fourth row of the table. This is where the complexity manifests itself. There is again a periodicity of 8 electrons in the fourth level, but there's a twist: the third level, even though it made it to a full shell, still has some extra space. Specifically, there is room for 10 more electrons. So the fourth row starts with elements 19 and 20, with one and two valence electrons, respectively, but then elements 21 through 30 are inserted into a middle ground, leftover from the third level. The regular sequence then begins again, as elements 31 through 36 round out the fourth row.
- 8). Fill in the fifth row, a repeat of the fourth row, which takes you from element 37 through 54. The sixth and seventh rows bring in another round of complexity, with the rare earths inserted into the pattern of the fourth and fifth rows.
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