Atomic Radius
Part of the Atomic Structure section of Coddy's Chemistry journey. Lesson 37 of 45.
The atomic radius is the size of an atom: how far its outer electrons sit from the nucleus.
Down a group, atoms get larger, because each period adds a new shell farther out: Li has 2 shells, Na 3, K 4.
Across a period, atoms get smaller. The number of shells stays the same, but each step adds a proton, and the stronger nucleus pulls the electrons in.
Atomic radius: larger down a group, smaller across a period
So the largest atoms are at the bottom left of the table and the smallest at the top right. Noble gases are left out of radius comparisons.
Challenge
A model kit has balls for five atoms: sodium, magnesium, phosphorus, chlorine and potassium. Put them in order of atomic radius, the largest first.
Try it yourself
Test yourselfThis lesson includes a short quiz. Start the lesson to answer it and track your progress.
All lessons in Atomic Structure
1Matter and Atoms
What Everything Is Made OfElements, Compounds, MixturesChemical SymbolsCounting Atoms in a FormulaRecap - Molecule Kit