身近な科学
Why are atoms different sizes?
A sodium atom is larger than a chlorine atom in the same period because effective nuclear attraction increases across the row.
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短い答え
A sodium atom is larger than a chlorine atom in the same period because effective nuclear attraction increases across the row.
本当は何が起きている？
Across period 3, atomic size generally falls while first ionization energy generally rises, with instructive exceptions.
役立つイメージ
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Atomic size reflects a competition between nuclear attraction, electron shielding and which shells are occupied. That is why radius changes systematically—but not perfectly smoothly—across the periodic table.