Modern periodic table: groups and periods
Periodic Classification and Periodicity · Chemistry
Study notes
Where is phosphorus (Z=15) in the table? Predict its chemistry. Step 1: Electron config: 1s²2s²2p⁶3s²3p³ → outermost shell n=3 → period 3. Step 2: 5 valence electrons (3s²3p³) → group 15, p-block. Step 3: Below nitrogen, above arsenic → forms PCl₃/PCl₅ like NCl₃, AsCl₃. Step 4: Position predicts properties — the table's whole point!