You know the periodic table that hung on the wall of every science class you took at school? As of today, it’s wrong. Or more precisely, it's inaccurate.

Chlorine is a halogen in group VII A of the periodic table with atomic number 17, an atomic weight of 35.45, and a density of 1.56 Mg/m 3. In the solid state it forms a tretragonal crystal with a ...