Complex Ions, Ligands and Their Shapes · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.
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Ligands, shapes and isomers

Science · Chemistry · ages 17-18
Name ______________________   Date ____________

  1. What is the coordination number of [Cu(H2O)6]2+?

    • 2
    • 4
    • 6

  2. What is a ligand?

    • A particle that donates a lone pair to a metal
    • A metal ion that accepts a lone pair from another particle
    • A particle that shares a pair from the metal's d sub-shell

  3. In cis-Pt(NH3)2Cl2, the two chloride ligands sit opposite each other across the square.

    Circle one:   True   False

  4. Which ligand is bidentate?

    • Water
    • Ethane-1,2-diamine
    • Chloride

  5. Why does [CuCl4]2- take a tetrahedral shape instead of octahedral?

    • Chloride ligands are too bulky for six to fit
    • Copper(II) ions are too small to hold more than four ligands
    • Each chloride binds through two atoms, so four fill all the sites

  6. Three ethane-1,2-diamine ligands replace the six waters on Cu2+. Why is the new complex more stable?

    • Ethane-1,2-diamine is a smaller ligand, so more of them fit
    • The swap raises the number of free particles from 4 to 7
    • The copper changes to a higher oxidation state with these ligands

  7. A new square planar drug works only as the cis form. A student says the trans form is worth testing as the same drug. What is the flaw?

    • Trans forms always break down before they can reach a tumour
    • Shape can decide drug action, as cisplatin versus trans shows
    • Cis and trans are one compound drawn two ways, so they act alike

  8. A student labels [CuCl4]2- as octahedral with coordination number 6. What is wrong?

    • Nothing, since copper complexes are octahedral with any ligand at all
    • It holds 4 chlorides, so the number is 4 and the shape is tetrahedral
    • It holds 4 chlorides, so the number is 2 and the shape is linear
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Ligands, shapes and isomers W1-mt_xxWYYqgZp_-s1

  1. 6 · Six waters each bond once, so the count is 6.
  2. A particle that donates a lone pair to a metal · A ligand gives its lone pair into an empty metal orbital.
  3. False · Cis means the matching ligands sit side by side. Chlorides opposite each other across the square would be the trans form, so the sentence is false.
  4. Ethane-1,2-diamine · Ethane-1,2-diamine binds through two atoms. The others bind through one.
  5. Chloride ligands are too bulky for six to fit · Four bulky chlorides fit tetrahedrally, while six small waters fit octahedrally.
  6. The swap raises the number of free particles from 4 to 7 · One complex plus three diamines becomes one complex plus six waters, so free particles rise from 4 to 7. Entropy increases, which favours the bidentate complex. This is the chelate effect.
  7. Shape can decide drug action, as cisplatin versus trans shows · Cisplatin shows this: the cis form fights tumours and the trans form does not.
  8. It holds 4 chlorides, so the number is 4 and the shape is tetrahedral · Four ligands give coordination number 4, and bulky chlorides arrange tetrahedrally.
Worksheet · LightMySky