Chromate ion
Charge: 2- · Type: Polyatomic anion · Molar mass: 115.992 g/mol
Made of: chromium, oxygen
How it forms
Chromium in the +6 state bonds tetrahedrally to four oxygens. Adding acid joins two chromate ions into one dichromate ion (Cr2O7^2-), and adding base reverses the change.
Naming note
CrO4^2- is the chromate ion; Cr2O7^2- is dichromate. Both contain toxic chromium(VI), so their compounds need careful handling.
Examples in compounds
Potassium chromate
Sodium chromate
Lead(II) chromate