Grade 11 · Chemistry
The periodic table and trends
Why it matters
Organizing the elements; trends in size, ionization energy and electronegativity.
Core20m readingPrerequisite: Electron configuration
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.
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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.