Periodic Trends
Periodic trends describe how properties change across periods and down groups. Master atomic radius, ionization energy, electronegativity, electron affinity, and metallic character.
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Study Tips
- ✓Most trends are explained by effective nuclear charge and shielding
- ✓Atomic radius decreases across a period, increases down a group
- ✓Ionization energy and electronegativity increase across and up
- ✓Cations are smaller than parent atoms; anions are larger
Common Mistakes to Avoid
Students often confuse trends for atomic vs ionic radius, forget that noble gases don't follow electronegativity trends, mix up ionization energy with electron affinity, and don't consider electron configuration anomalies (like Cr and Cu).
Periodic Trends FAQs
Common questions about periodic trends
Across a period, protons are added to the nucleus while electrons are added to the same shell. The increased nuclear charge pulls electrons closer, decreasing radius. Shielding remains roughly constant since electrons are added to the same shell.
The first electron removed from Na is the single 3s valence electron. The second electron must come from the stable 2p^6 core, which requires much more energy because these electrons are closer to the nucleus and experience less shielding.
Effective nuclear charge (Zeff) is the net positive charge experienced by an electron. Zeff = Z - S, where Z is atomic number and S is shielding from other electrons. Core electrons shield effectively; valence electrons barely shield each other.
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