Orbital Blocks in the Periodic Table

You can see that the number of columns in a block corresponds to the maximum number of electrons that can occupy the particular sublevel of that block. The s block has 2 columns (corresponding to one s orbital holding a maximum of two electrons) the p block has 6 columns (corresponding to threep orbitals with two electrons each) the d block has 10 columns (corresponding to five d orbitals with two electrons each) and the/block has 14 columns (corresponding to seven / orbitals with two electrons each). 

Notice also that, except for hehum, the number of valence electrons for any main-group element is equal to its lettered group number. We can tell that chlorine has seven valence electrons because it is in group number 7A. 

Lastly, note that, for main-group elements, the row number in the periodic table is equal to the number (or n value) of the highest principal level. For example, because chlorine is in row 3, its highest principal level is the = 3 level. 

Recall from Chapter 2 that main-group elements are those in the two far left columns (groups lA, 2A) and the six far right columns (groups 3A-8A) of the periodic table. 

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