Final answer:
The trend in atomic radii within a period is that it generally decreases from left to right across the period due to the increase in nuclear charge attracting the electrons more strongly.
Step-by-step explanation:
The trend in atomic radii within a period is that the atomic radius generally decreases from left to right across the period. This is due to the increase in the number of protons in the nucleus as one moves from left to right. The increased positive charge of the nucleus attracts the electrons more strongly, pulling them closer to the nucleus, and resulting in smaller atomic size.
However, there are some small exceptions to this trend, such as the oxygen radius being slightly greater than the nitrogen radius. This can be attributed to electron-electron repulsions that cause the atom's size to increase even though the nuclear charge is increasing. Overall, the trend in atomic radii within a period is a decrease as Z (atomic number) increases.