Question

In two or more complete sentences describe how atomic radius changes as you move across a period in the periodic table and why.

Answer 1

Periodic Trend. The atomic radius of atoms generally decreases from left to right across a period. ... Within a period, protons are added to the nucleus as electrons are being added to the same principal energy level. These electrons are gradually pulled closer to the nucleus because of its increased positive charge.

Answer 2

Due to effective nuclear charge  size of an atom decreases along the period.

As the electrons and protons increase they attract each other and thus the size shrinks.