Periodic Trends UPCAT Reviewer: Lesson and Practice
Periodic Trends
Use direction and cause—not three unrelated arrows—to compare elements.
Periodic Trends
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Position predicts general patterns
Across a period, nuclear charge increases while electrons enter the same principal energy level. Down a group, new energy levels and shielding place valence electrons farther from the nucleus.
Atomic radius
Generally increases down a group and toward the left.
Ionization energy and electronegativity
Generally increase up a group and toward the right.
Radius runs down-left; attraction runs up-right
Why it works
Smaller, less-shielded atoms generally exert a stronger attraction on valence or bonding electrons.
Five forms you should recognize
Na is larger; Cl generally has higher ionization energy and electronegativity.
K is larger; Li has higher ionization energy.
F is more electronegative because it is higher in the group.
Effective nuclear charge rises without adding a new principal shell, so radius generally falls.
Additional shells increase distance and shielding, so radius rises.
Check before you commit
- Reversing the radius arrow
- Using atomic mass alone
- Forgetting that trends are general patterns
- Assuming more protons always means a larger atom
- Combining across-period and down-group reasoning incorrectly
- Ignoring shielding
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Foundations
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Core Practice
Use mixed forms with less scaffolding.
UPCAT-Style Transfer
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Periodic Trends FAQ
Are there exceptions?
Yes. Electron configuration creates exceptions, especially in detailed ionization-energy comparisons.
Why exclude noble-gas electronegativity in basic comparisons?
Many introductory scales do not assign conventional values because noble gases rarely form bonds.
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