Block: definition in chemistry
Block: One of four regions of the periodic table, the s-, p-, d- and f-blocks, named after the type of subshell that holds each element's highest-energy electrons.
The s-block holds groups 1 and 2 plus helium, the p-block groups 13 to 18, the d-block groups 3 to 12 and the f-block the lanthanides and actinides. The width of each block, 2, 6, 10 or 14 columns, equals the number of electrons its subshell can hold. Elements in a block share broad traits: apart from hydrogen and helium the s-block elements are reactive metals, the p-block contains every other nonmetal, and the d- and f-block elements are all metals.
Examples
- Sodium (s-block) — [Ne] 3s¹
- Chlorine (p-block) — [Ne] 3s² 3p⁵
- Iron (d-block) — [Ar] 3d⁶ 4s²
- Uranium (f-block) — [Rn] 5f³ 6d¹ 7s²
On the periodic table
Blocks divide the table into four zones: two columns on the left (s), six on the right (p), ten in the middle (d) and the two rows of 14 set below the main table (f).