What trend is observed in the lower left section of the periodic table?

In the lower left section of the periodic table, which includes elements such as alkali metals and alkaline earth metals, the trend observed is that the atomic radius increases. As you move down a group in the periodic table, additional electron shells are added, which results in a greater distance between the nucleus and the outermost electrons. This increase in distance causes the atomic size to expand.

Moreover, the effective nuclear charge experienced by the outermost electrons does not increase in proportion to the addition of electron shells, leading to less pull on the outer electrons. Hence, the overall size of the atoms increases as you descend the periodic table, particularly in the regions where larger atomic structures, such as those in the lower left section, are found.

In contrast, as you move from left to right across a period, the atomic radius generally decreases due to an increase in nuclear charge without a corresponding increase in shielding, pulling the electrons closer to the nucleus. This explains the distinct trend observed specifically in the lower left part of the table where atomic size continues to grow larger as you go down.