Final answer:
The atomic radius decreases across a period due to increased nuclear attraction and increases down a group due to additional occupied principal energy levels. The largest atoms are in the lower left of the periodic table, while the smallest are in the upper right corner.
Step-by-step explanation:
The trend of the atomic radius within the periodic table is an important concept in understanding the structure of atoms. Across a period, the atomic radius generally decreases as the atomic number (Z) increases, such as from potassium (K) to krypton (Kr).
This decrease is due to the addition of protons to the nucleus and electrons to the same principal energy level, leading to a greater force of attraction pulling the electrons closer to the nucleus.
In contrast, the trend down a group is that the atomic radius increases as the atomic number increases. This increase is a result of additional occupied principal energy levels, which have larger orbitals compared to lower energy levels.
The effect of these additional principal energy levels is greater than the increased nuclear charge, resulting in an increase in atomic radius down the group.
Overall, atoms tend to be smaller as one moves from left to right across a period and larger as one moves from top to bottom down a group. The largest atoms are found in the lower left corner of the periodic table, and the smallest in the upper right corner.