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How does atomic size change from the upper right to the lower left of the periodic table?
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periodic table
Modern version of the periodic table of the elements. To learn an element's name, atomic number, electron configuration, atomic weight, and more, select one from the table.
Atomic size increases as you move from the upper right to the lower left of the periodic table. Consequently, the smallest atoms are located at the upper right, while the largest atoms are found at the lower left.12
This trend is driven by two primary factors:
- Vertical Trend: Moving down a group, atomic radius increases because electrons are added to new, outer shells, effectively increasing the size of the atom.1
- Horizontal Trend: Moving from left to right across a period, atomic size generally decreases. Although more electrons are added, the increasing positive nuclear charge pulls the valence electrons closer to the nucleus, resulting in a more compact atom.1
The competition between these effects results in the observed trend where atoms become progressively larger as one moves toward the bottom-left corner of the table.12