Final answer:
As you go across a period on the periodic table, the atomic radii generally decrease due to the increase in nuclear charge, which outweighs the increase in electron shells. An example of this is the comparison between lithium and neon.
Step-by-step explanation:
As you go across a period on the periodic table, the atomic radii generally decrease. This is because the number of protons in the nucleus increases, which attracts the electrons more strongly and pulls them closer to the nucleus. The increase in nuclear charge outweighs the increase in electron shells, resulting in smaller atomic radii.
An example of this trend can be seen when comparing the atomic radius of lithium (Li) and neon (Ne). Lithium is located towards the left side of period 2, while neon is towards the right. The atomic radius of lithium is larger than the atomic radius of neon because lithium has fewer protons and a smaller nuclear charge, allowing its electrons to be more loosely held.