Transition Metals Lesson

Tranisiton metals L1-4

Summary Lesson

Covered so far...

• Intro to transition metals

• Formation of complex ions

• Formation of coloured compounds

• Variable oxidation states and REDOX

Introduction to transition metals

• Definition

• Electronic structure

• Properties

Open Ended

What is the definition of a transition metal?

Transition metal:

An element that has an incomplete d-sub shell in either its atoms or its common ions

Multiple Choice

Which one of the following electronic configurations is that of a transition element?

• [Ar] 4s²3d¹⁰

• [Ar] 4s²3d⁹

• [A] 4s²3d⁰

• [Ar] 4s²3d¹⁰4p¹

Multiple Choice

What is the electronic structure of the Cu(II) ion?

• [Ar]3d⁹4s²

• [Ar]3d104s1

• [Ar]3d9

• [Ar]3d10

Poll

How do you feel about electronic structures?

• Good

• OK

• HELP!

Complex ions

• Definitions

• Coordinate bonds

• Types of ligand

• Shapes of complexes

• Haemoglobin

Fill in the Blank

A ligand is a particle with a ____ _____ that bonds to metals

Fill in the Blank

A ligand bonds to a metal by a ________ bond

Multiple Choice

What is the co-ordination number

• The number of co-ordinate bonds formed by ligands

• The number of ligands attached to the metal

• The charge of the metal

• The oxidation number of the transition metal

Multiple Choice

What is the name of a complex ion with 2 ligands

• Linear

• Square planar

• Tetrahedral

• Octahedral

Multiple Choice

What is the name of a complex ion with 4 ligands and a 90 degree angle

• Linear

• Square planar

• Tetrahedral

• Octahedral

Multiple Choice

What is the name of the following complex ion [Cu(H2O)6]2+

• Linear

• Square planar

• Tetrahedral

• Octahedral

Isomerisim in complex ions

• Cis/Trans isomerism is shown in octahedral adn square planar complexes where there are two lignads of one type different to the rest of the ligands

• Optical isomerismoccurs in octahedral complexes with three bidentate ligands

Ligand Substitution

• When one ligand is replaced by another ligand

• If the ligands are similar sizes (ie H₂O and NH₃) the co-ordination number usually stays the same.

• If the ligands are different sizes the co-ordination number may change.

• Cl- is much larger than O in H2O or N in NH3

• [Co(H₂O)₆]²⁺ + 4Cl^- -> [CoCl₄]^2- + 6H₂O

Chelate Effect

• Many ligand substitution reactions are easily reversed

• However some complex ions are more stable than others

• If the new ligand forms stronger bonds with the metal ion it is harder to reverse. (ie carbon monoxide bonding to Fe²⁺ in haemoglobin)

• Multidente ligands form more stable complexes than monodentate ligands

The Chelate Effect

• When a monodentate ligand is substituted for a multidentate ligand the enthalpy change is very small. (similar bonds)

• ie [Cr(NH₃)₆]³⁺ + 3NH₂CH₂CH₂NH₂ -> [Cr(NH₂CH₂CH₂NH₂)₃]³⁺ 6NH₃

• However as you can see there is an increase in entropy (4 particles to 7 particles)

• Using what you know about gibbs free energy if enthalpy change is small and entropy change is very positive then the reaction is likely to occur

•  $\Delta G\ =\ \Delta H\ -\ T\Delta S$  

Multiple Choice

Which statement is correct about this reaction?

[Co(NH₃)6]²⁺ + 3H₂NCH₂CH₂NH₂ → [Co(H₂NCH₂CH₂NH₂)₃]²⁺ + 6NH₃

• The co-ordination number of cobalt decreases.

• The enthalpy change is large and positive.

• The entropy change is large and positive.

• The shape of the complex changes from octahedral.

Multiple Choice

Solution A contains the compound [Cu(H₂O)₆]Cl₂

State the type of bonding between the oxygen and hydrogen in this compound.

• Coordinate

• Dative Covalent

• Covalent

• Ionic

Multiple Choice

Hexaaquairon(II) ions react with an excess of H₂NCH₂CH₂NH₂ in a ligand substitution reaction.

Which of the following shows the correct change in entropy for a reaction of hexaaquairon(II) ions with H₂NCH₂CH₂NH₂?

• change in entropy is negative

• change in entropy is close to zero

• change in entropy is positive

Fill in the Blank

In aqueous solution, the [Co(H₂O)₆]²⁺ ion reacts with an excess of ethane-1,2-diamine to form the complex ion Y.

(i) Write an equation for this reaction.

Open Ended

Hexaaquairon(II) ions react with an excess of H₂NCH₂CH₂NH₂ in a ligand substitution reaction.

Explain, in terms of the chelate effect, why the complex ion Y is formed in preference to the [Co(H₂O)₆]²⁺ complex ion.

The number of particles increases / changes from 4 to 7

So the entropy change is positive / disorder increases / entropy increases

Coloured Compounds

• In Transition metal compounds the 5 d orbitals do not all have the same energy

• This gap in energy corresponds to the energy of a part of the visible spectrum

• The colour that you see is a mixture of the colours NOT absorbed

• The colour is affected by - Metal, Oxidation state, Ligands, Co-ordination number

Fill in the Blank

Name the technique used to determine the concentration of a coloured compound