posted by Anonymous .
please help!!! im confused... can you explain to me how period and group trends in atomic radii are related to electron configuration? is it because as you move down the table the atomic radius increases and as you move across the table from left to right, atomic radius decreases?
Yes it is but I think your confusion may result in your reasoning. The fact you quoted is the RESULT of the trends in electron configuration.
The reason the radii increase as one moves DOWN the table is because additional shells are being filled. (Note that H has just 1 shell (n=1), Li has two shells (n = 1 and 2), Na has three (period 3) etc. The reason radii decreases as one moves from left to right in the table is because the atomic number (number of protons in the nucleus) is increasing but the shell remains the same; therefore, the increasing positive charge in the nucleus is pulling the electrons closer.