# How do you think the atomic radii will change as electrons are added to a shell?

##### 1 Answer
Jan 23, 2016

As electrons are added to the shell across the Period, atomic radii should DECREASE why?

#### Explanation:

I assume you describe a Periodic trend. As electrons are added to the valence shell, an extra proton (i.e fundamental, positively charged nuclear particle) is added to the element's nucleus. As electrons add and $Z$ the atomic number increases 1 by 1, nuclear charge WINS, and electronic radii contract. The result is the well-established CONTRACTION of atomic radii ACROSS a PERIOD.

One a Period is full, the full electron shell effectively shields the increased nuclear charge, and the next valence shell of electrons is further distant from the atomic nucleus. What is described here is the rationale for the observation that ATOMIC radii decrease across a Period (going from left to right) BUT increase down a Group.

Of course, if we discuss the same element, the reduced element (i.e. the element with 1 or 2 or 3 extra electrons , should be larger than the neutral element. Why?