What do all the elements in a horizontal column of the periodic table have in common?
Rows are horizontal; columns are vertical......
Columns on the Periodic Table dictate the same valence electronic shell, i.e. the same electronic shell. The number of the columns, which chemists call
A horizontal row on the Periodic Table is called a Period; and in the same Period, electrons fill the SAME valence shell. To go a bit farther, the first shell can accommodate 2 electrons to form the first electronic shell, and hence a Period of the Table has been described; the second valence shell can accommodate up to 8 electrons.........and so on.
This electronic structure dictates why, and the way we write the Periodic Table. Full valence shells, i.e. the element has 2 OR 10 electrons, are stable electronic structures.