Copper(II)
The Roman numeral identifies copper's +2 oxidation state.
That distinguishes CuSO₄ from compounds containing copper in other oxidation states.
Ionic solid · sulfate salt
Copper(II) sulfate
CuSO₄
Copper(II) sulfate is CuSO₄, an ionic solid built from Cu²⁺ and SO₄²⁻ in a 1:1 ratio. The sulfate ion contains its own covalent sulfur–oxygen framework.
Hydrate distinction: this master represents anhydrous CuSO₄. Copper(II) sulfate pentahydrate is CuSO₄·5H₂O and is a distinct crystalline form with water incorporated into the solid.
Essentials
CuSO₄ is one Cu²⁺ ion for one SO₄²⁻ ion.
The +2 and −2 charges balance in a 1:1 formula unit. The solid should not be pictured as a discrete six-atom CuSO₄ molecule.
Detail
Sulfate is tetrahedral and internally covalent.
Four oxygen positions surround sulfur in the sulfate ion. Resonance-style descriptions avoid assigning one permanent unique S–O double bond.
Coordination in real crystals
Cu²⁺ is surrounded by oxygen donors in the solid-state structure.
The exact coordination environment depends on hydration state and crystal form.
Understand
Hydration state is part of the solid's chemical description.
Adding waters of crystallization changes both formula mass and crystal structure. Anhydrous CuSO₄ and CuSO₄·5H₂O should therefore not be merged into one formula entry.
Color caution
The familiar blue crystalline material is commonly the pentahydrate.
Color depends strongly on copper's coordination environment, so hydration changes more than just mass.
Reference identifiers
Names and identifiers that pin down the chemical identity.
| Formula | CuSO₄ |
|---|---|
| CAS Registry Number | 7758-98-7 |
| Form represented | anhydrous copper(II) sulfate |
| Common hydrate | CuSO₄·5H₂O |
Advanced
Push past the first model without losing the simple picture.
Is CuSO₄·5H₂O just wet CuSO₄?
No. The pentahydrate is a defined crystalline hydrate with stoichiometric water.
Is sulfate molecular inside the crystal?
SO₄²⁻ is a covalently bonded polyatomic ion embedded in an ionic solid.
Why write copper(II)?
The Stock numeral II specifies Cu in oxidation state +2.
Constituent elements