Periodic Trends - Atomic Radius
Topics Covered: periodic trends, atomic radius, effective nuclear charge, shielding effect
Did you know that the radii of atoms have patterns across the periodic table? Today, we’re back with the periodic trends series and will discuss the periodic trends of atomic radius.
One thing to note before we start our discussion: this post is written on the assumption that you are familiar with all the concepts that help explain periodic trends (mainly effective nuclear charge for today), so if you are unfamiliar with that concept, please refer to our previous post on ionization energy!
As you move from left to right of the periodic table, the effective nuclear charge increases since the number of protons in the nucleus increases. This means the electrons will be drawn closer to the nucleus. Because the nucleus is pulling electrons tighter than before, this would decrease the atomic radii!
If you move from top to bottom of the periodic table, the energy levels of the atoms increases. Because of this increase in energy level, the atomic radius would also increase! This trend can also be explained with a shielding effect. Going from top to bottom of the periodic table, there is an increase in the shielding of the nucleus by the core electrons, which would decrease the attraction between the nucleus and valence electrons and thus increase the atomic radius.
To summarize, the trends in atomic radius is the opposite of the trends in ionization energy. Atomic radii decrease from left to right of the periodic table, and increase from top to bottom of the periodic table!
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