Electron configuration
The s, p, d and f blocks reflect the type of subshell associated with electron filling. Helium is a useful exception: it is in group 18 because of its chemistry, but its 1s² configuration places it in the s block.
Blocks link the table to electron configuration
The s, p, d and f blocks reflect the type of subshell associated with electron filling. Helium is a useful exception: it is in group 18 because of its chemistry, but its 1s² configuration places it in the s block.
Sodium has Z = 11, is in period 3, group 1 and the s block. Its ground-state electron configuration is 1s² 2s² 2p⁶ 3s¹.
What can be inferred for chlorine?
Chlorine has Z = 17, lies in period 3 and group 17, and its configuration ends in 3s² 3p⁵. It therefore has seven valence electrons in its ground state and commonly forms Cl⁻.
3s² 3p⁵ · Cl⁻
Use the table as a structured summary
Position helps identify chemical families, electron patterns and broad trends. Precise reactivity, toxicity, melting point or the behaviour of a compound require additional data and models.