Skip to main content

Werner's postulates; IUPAC names [partly illegible]

Short answer

Metals have primary valency (ionisable, equals oxidation state) and secondary valency (non-ionisable, equals coordination number, directed in space). IUPAC names: (a) tetraamminediaquacopper(II) ion, (b) diaquatetrahydroxocobaltate(III) ion, (c) hexaamminecobalt(III) chloride, (d) potassium tetracyanonickelate(II).

What are the main postulates of Werner's theory? W[?] following complexes. a) [Cu(NH₃)₄(H₂O)₂]²⁺ b) [Co(H₂O)₂(OH)₄]⁻ c) [Co(NH₃)₆]Cl₃ d) [?]₂[Ni(CN)₄]

Reading: the question is "What are the main postulates of Werner's theory? Write the IUPAC names of the following complexes." Part (d) has an illegible cation; I take it as K₂[Ni(CN)₄].

Main postulates of Werner's theory

  1. A metal in a complex shows two kinds of valency: primary (ionisable) valency, which is equal to the oxidation state and is satisfied by negative ions; and secondary (non-ionisable) valency, which is equal to the coordination number and is satisfied by negative ions or neutral molecules (ligands).
  2. Every metal tries to satisfy both its primary and secondary valencies.
  3. The secondary valencies are directed in space, so each complex has a definite geometry: coordination number 6 gives an octahedral complex, and 4 gives a tetrahedral or square planar complex.
  4. Ligands that satisfy the secondary valency are attached directly to the metal inside the coordination sphere (written in square brackets) and do not ionise; the primary valency is satisfied by ions outside the sphere that ionise in water.

IUPAC names

a) [Cu(NH₃)₄(H₂O)₂]²⁺: tetraamminediaquacopper(II) ion b) [Co(H₂O)₂(OH)₄]⁻: diaquatetrahydroxocobaltate(III) ion c) [Co(NH₃)₆]Cl₃: hexaamminecobalt(III) chloride d) K₂[Ni(CN)₄]: potassium tetracyanonickelate(II)

✓ Answer checked by Claude Opus 5.5 (high effort)

Related questions

All Engineering Chemistry chapter 6 questions →