what is the trend in the atomic radii as the atomic number increases across a period? What is the exception to this trend?
I know the radius decreases as you go from left to right, but I can't figure the exception, I read somewhere that it's the noble gasses but I'm not sure.
The trend in atomic radii as the atomic number increases across a period is that the atomic radius generally decreases. This is primarily due to the increase in effective nuclear charge, meaning that as you move across a period, the number of protons in the nucleus increases, resulting in a stronger attraction between the nucleus and the outermost electrons.
The exception to this trend is found in the noble gases. Noble gases, such as helium (He), neon (Ne), argon (Ar), etc., have completely filled electron shells, making them highly stable. Since these elements have the maximum number of electrons in their outermost energy level, they do not readily participate in chemical reactions and do not tend to gain or lose electrons. As a result, their atomic radii are larger compared to the elements in the same period.
To verify this information, you can reference a periodic table or use an online resource. Simply find the atomic radii values for each element in a specific period, and you will observe that as you move from left to right, the atomic radii generally decrease with the exception of the noble gases.