#"Increase in atomic radii down a Group, a column of the Periodic"# #"Table."#
The chemistry and atomic structure of the elements is a contest between (i) nuclear charge, conveniently represented by #Z_"the atomic number"#, and (ii) shielding by other electrons. Now it is a fact that the nuclear charge is SHIELDED very poorly by incomplete electronic shells. And the best metric that illustrates this trend is the well-known diminution of atomic radii across the Period from left to right? And of course, we should look at some data.
Of course, the diagram shows NO data (it should do so), but the relative size of the atoms across the Period, and down the Group is clear. It follows that the SMALLEST atoms derive the right of the Table as we face it. Excluding the Noble Gases, the smaller atoms from the right hand side, i.e. nitrogen, fluorine, oxygen, TEND to be very powerful oxidants, and this is also manifested by their small atomic size.
On the other hand, the larger elements, i.e. alkali, and alkaline-earth metals, tend to be good reducing agents, as their valence electrons, whose radial orbit DEFINES the atomic radius, tend to be readily oxidized.