High school10 min

Periodic trends: radius, ionisation, electronegativity

Compare two elements without a data table: atomic radius, ionisation energy and electronegativity follow from effective charge and the number of shells.

The essentials

1

Effective nuclear charge

A valence electron does not feel the whole of ZZ: the core electrons shield it. Z∗=Z−σZ^* = Z - \sigma Across a period, ZZ rises by one unit per box while σ\sigma rises far more slowly: Z∗Z^* increases from left to right. Down a group, what dominates is the extra shell, farther from the nucleus.
2

Atomic radius

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3

Ionic size

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4

First ionisation energy

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5

Electronegativity

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