Module elements 

Periodic table: atomic number ↔ element symbol.

Index 0 is the wildcard / dummy atom (*). Indices 1..=118 are H..=Og.

Constants

SYMBOLS

Symbols by atomic number (0 → *, 1 → H, … 118 → Og).

Functions

atomic_number

Atomic number for an element symbol (case-insensitive). "*" / "R" → 0.

element_symbol

Element symbol for atomic number z. Unknown z → "X".