Overview
This lecture covers the periodic trends of atomic size and ionization energy, explaining how and why these properties change as you move across or down the periodic table.
Atomic Size Trends
- Atomic size is measured from the nucleus to the outermost electron.
- As you go down a group in the periodic table, atomic size increases due to the addition of electron shells.
- As you go across a period (left to right), atomic size decreases because more protons pull electrons closer, shrinking the atom.
- Example: Sodium is larger than lithium because sodium has more electron shells.
Ionization Energy Trends
- Ionization energy is the energy required to remove the outermost (easiest) electron from an atom.
- Atoms with outer electrons farther from the nucleus (larger atoms) have lower ionization energy.
- As you go down a group, ionization energy decreases because the outer electron is farther from the nucleus and easier to remove.
- As you go across a period, ionization energy increases because atoms are smaller and electrons are held tighter by the nucleus.
- Atomic size and ionization energy show opposite trends on the periodic table.
Key Terms & Definitions
- Atomic size — the distance from the nucleus to the outermost electron of an atom.
- Ionization energy — the energy required to remove the most loosely held electron from a neutral atom.
- Periodic trend — a predictable change in a property of elements within the periodic table as you move across or down.
Action Items / Next Steps
- Review periodic table trends for atomic size and ionization energy.
- Practice identifying these trends for various elements on the periodic table.