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Periodic Trends

▶︎  Watch it animatedinteractive step-through · ~3 min · optional

The periodic table's layout predicts behavior. As you move across a period and down a group, atomic radius, ionization energy, and electronegativity shift in patterns that all trace back to two competing effects: growing nuclear charge pulling electrons in, and added shells and shielding pushing them out. Learn the two forces and the trends follow.

UNIT 1 TOPIC 1.7 • PERIODIC TRENDS TREND SURFER PERIODIC TABLE MAP ACROSS → IE · EN · EA increase DOWN ↓ radius increases F ★ bottom-left = LARGEST atomic radius ★ top-right = HIGHEST IE / EN / EA (excl. noble gases) TREND DIRECTIONS ATOMIC & IONIC RADIUS ↓ down a group, ← across (left) IONIZATION ENERGY (IE₁) ↑ up a group, → across (right) ELECTRONEGATIVITY (EN) ↑ up a group, → across (right) ELECTRON AFFINITY |mag| ↑ up, → right (excl. noble gases) Na [Ne] 3s¹ radius: LARGE IE₁ = 496 kJ/mol loses e⁻ easily (LOW IE) Cl [Ne] 3s² 3p⁵ radius: SMALL IE₁ = 1251 kJ/mol holds e⁻ tightly (HIGH IE) vs IONIC RADIUS Na > Na⁺ cation smaller Na⁺ < Na · Cl⁻ > Cl → anions are larger WHY? EFFECTIVE NUCLEAR CHARGE (Zₑff) Across →: Zₑff ↑ → smaller r, higher IE/EN Down ↓: more shells + shielding → larger r, lower IE/EN CED ANCHOR SAP-2 · periodic trends (radius, IE, EN) follow from Coulombic attraction, Zₑff, and shielding. AP Chemistry · Unit 1 · Atomic Structure & Properties
The trend map. Moving down a group adds shells, so atomic radius grows; moving across a period pulls electrons in harder, so radius shrinks while ionization energy and electronegativity rise. The bottom-left holds the largest atoms; the top-right (noble gases aside) the most tightly held.
Trend Surfer · Open the sandbox →

Trends are reasoned, not memorized. The reliable move is to ask which wins for a given comparison, the stronger pull of a higher nuclear charge or the extra distance and shielding of another shell, and to remember that these are general tendencies with well-known exceptions rather than strict laws.

The work

3 ways in · any order
Lesson
Periodic Trends ›

Radius, ionization energy, and electronegativity all follow from nuclear charge versus shielding. The lesson reasons each trend from those two forces, then closes with a ten-scenario applet that compares atoms across and down the table.

Skill check · 10 scenarios
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Diagnostic
10-item topic check ›

Ten items on the periodic trends: ranking atomic and ionic radius, ionization energy, and electronegativity across periods and down groups, and reasoning each ordering from nuclear charge and shielding rather than position alone.

Not started · 10 items · ~15 min
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Targeted Practice
Drill a single misconception ›

Pick one of the failure modes you missed and drill it on its own. The round is adaptive: two correct in a row clears the misconception and moves you to the next.

Take the diagnostic to identify your misconceptions
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