Periodic Trends: Atomic Radius, Electronegativity and Ionization Energy
Learn how atomic radius, electronegativity and ionization energy change across and down the periodic table, with two worked examples.
Atomic radius
- Across a period: decreases
- Down a group: increases
More protons pull electrons in across. More shells push out going down.
Electronegativity and ionization energy
- Both increase across a period
- Both decrease down a group
- Fluorine is the top-right extreme
Strong pull and a hard-to-remove electron go together.
Example 1
Which has the larger atomic radius, Na or Cl?
- Both are in period 3
- Radius decreases across a period, so Na is on the larger side
Na
Example 2
Which is more electronegative, F or O?
- Both are in period 2
- Electronegativity increases across a period
F
Common mistake
Atomic radius increases from left to right
It decreases across a period.
It only increases as you go down a group.
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