Chemistry 11 · Chemistry · Lesson 7.4
Periodic trends and electronegativity
- Level
- Grade 11
- Reading time
- 15 min reading
- Review
- Last reviewed 2026-09-03
- Standard
- Accuracy standard
- Errata
Abstract
Organizing the elements; trends in size, ionization energy and electronegativity.
What are periodic trends?
Short answer
Periodic trends are patterns in element properties across the periodic table that follow from atomic structure. Moving across a period, atomic radius decreases while ionization energy and electronegativity increase; moving down a group, atomic radius increases while ionization energy and electronegativity decrease. These trends arise from changing nuclear charge and the number of electron shells.
Concept preview
What you will be able to do
- 01Explain how the periodic table is organised and the periodic law
- 02Describe the trend in atomic radius across and down the table
- 03Describe the trends in ionization energy and electronegativity
By the mid-1800s dozens of elements were known, and chemists sought a way to organise them. Early attempts grouped elements by similar properties — Döbereiner's triads and Newlands' 'octaves' — hinting that properties repeat periodically. A period is a horizontal row and a group (or family) is a vertical column of the table.
School Plan
Periodic trends and electronegativity
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Related topics
Frequently asked questions
- Why does atomic radius decrease across a period?
- The growing nuclear charge pulls the electrons in the same shell closer, shrinking the atom.
- What is electronegativity?
- A measure of how strongly an atom attracts shared electrons in a bond; it increases across a period and decreases down a group.