Define ligand, denticity and coordination number. Find the coordination number of the metal in [CoCl₂(en)₂]⁺ and K₃[Fe(C₂O₄)₃].

How to lay out the answer. Follow the frame, then write it in your own words.

1 · Define a ligand. An ion or molecule bonded to the central atom by donating a lone pair of electrons.
2 · Define denticity, with examples. The number of donor atoms a ligand uses: NH₃ is unidentate, en is didentate, EDTA⁴⁻ is hexadentate.
3 · Define coordination number. The number of donor atoms bonded to the central atom by σ bonds.
4 · Work the first example. [CoCl₂(en)₂]⁺: 2 × 1 + 2 × 2 = 6.
5 · Work the second example. K₃[Fe(C₂O₄)₃]: 3 × 2 = 6.
6 · Close in one line. So the coordination number counts donor atoms; it equals the number of ligands only when all of them are unidentate.

Scoring tip: Show the multiplication (number of ligands × denticity). A bare answer of 6 can lose the working mark.