Atomic
radius is
generally stated as being the total distance from an atom’s nucleus to the
outermost orbital of electron. In simpler terms, it can be defined as something
similar to the radius of a circle, where the center of the circle is the
nucleus and the outer edge of the circle is the outermost orbital of electron.
As you begin to move across or down the periodic table, trends emerge that help
explain how atomic radii change.
Effective
Nuclear Charge:
The
effective nuclear charge (Zeff) of an atom is the net positive
charge felt by the valence electron. Some positive charge is shieled by the
core electrons therefore the total positive charge is not felt by the valence
electron. Zeff greatly affects the atomic size of an atom. So
as the Zeff decreases, the atomic radius will grow as a result
because there is more screening of the electrons from the nucleus, which
decreases the attraction between the nucleus and the electron. Since Zeff decreases
going down a group and right to left across the periodic table, the atomic
radius will increase going down a group and right to left across
the periodic table.