Topic 15 - TRANSITION METALS Flashcards
Definition of a transition metal
An element that has an incomplete d sub shell in its common ions
Which two period 4 d-block elements are not transition metals and why? (6)
- Transition metals are elements that have an incomplete d sub shell in its common ions
- Scandium forms Sc3+ ion
- Electronic configuration of Sc3+: 1s2 2s2 2p6 3s2 3p6
- In Sc3+, the d orbital is empty
- Zinc forms Zn2+ ion
- Electronic configuration of Zn2+: 1s2 2s2 2p6 3s2 3p6 3d10
- In Zn2+, the d orbital is completely full
- Therefore Zn and Sc are not transition metals
Electronic configuration of Cr using [Ar]
[Ar] 4s1 3d5
Electronic configuration of Cu using [Ar]
[Ar] 4s1 3d10
Describe and explain the properties of a transition metal
- High MP/BP
- High density
- High tensile strength
- Large nuclear charge
- Small atomic radius
- Strong electrostatic attraction
Why do transition metals have variable oxidation states?
- Energy difference between orbitals
- So both energy levels can be used for bond formation
Why do transition metals form coloured compounds?
- Gap in energy levels between d orbitals
- Electrons absorb energy to be promoted to higher energy level
- We see colour because of the visible light that is not absorbed
- The colour we see of solids is due to light being reflected
Identify 4 factors that affect the colour of transition metal complexes and explain why they affect colour
- Oxidation state
- Ligands
- Co ordination number
- Shape
All affect size of energy gap between d orbitals and wavelength of light absorbed
What does this equation stand for:
△E = hf = hc/λ
△E = gap in energy
h = Planck’s constant (6.63 x 10^-34 J)
f = frequency of light
c = velocity of light
λ = wavelength of light
Definition of a ligand
Particle with lone pair of electrons that bonds to metals by a co-ordinate bond
Definition of a complex
Metal ion with co-ordinately bonded ligands
Definition of co-ordinate number
Number of co-ordinate bonds from ligands to metal ion
What is the shape and angle of a complex with:
- Coordination number: 2
- Contains Ag+ ?
- Planar
- 180
What is the shape and angle of a complex with:
- Coordination number: 4
- Contains Pt 2+ and Ni 2+ ?
- Square planar
- 90
What is the shape and angle of a complex with:
- Coordination number: 4
- Contains larger ligands eg Cl- ?
- Tetrahedral
- 109.5
What is the shape and angle of a complex with:
- Coordination number: 6
- Contains small ligands eg. H2O ?
- Octahedral
- 90
What is a monodentate ligand and give examples?
- Ligand which has one pair of electrons they can donate to a central metal ion
- H2O
- NH3
- Cl-
- CN-
What is a bidentate ligand?
- Ligand which can form two dative bonds to the complex ion as it contains two lone pairs of electrons
What is a polydentate ligand and give examples?
- Ligand with more than two atoms with lone pairs of electrons and can form more than two dative bonds to the complex ions
- EDTA+
How can we identify cisplatin complexes from a diagram?
Similar ligands are next to each other
How can we identify transplatin complexes?
Similar ligands are opposite each other
What is a ligand substitution?
A reaction where one ligand is replaced by another ligand
What is the colour of [Cu(H2O)6]2+
Blue
What is the colour of [Fe(H2O)6]2+
Green
What is the colour of [Co(H2O)6]2+
Pink
What is the colour of [Fe(H2O)6]2+
Yellow
What is the colour of [Cr(H2O)6]3+
Green
What happens when excess OH- is added to group 2 metals?
White ppt forms
What is the colour of chromium (III) with some OH-?
Green ppt
What is the colour of chromium (III) with excess OH-?
Green ppt redissolves to dark green
What is the colour of iron (III) in OH-?
Green ppt which oxidises on standing
What is the colour of iron (III) in OH-?
Red/brown ppt
What is the colour of cobalt (II) in OH-?
Blue ppt which turns pink on standing
What is the colour of copper (II) in OH-?
Blue ppt
What is the colour of chromium (III) with some NH3?
Green ppt
What is the colour of chromium (III) in excess NH3?
Green ppt redissolves to form purple ppt
What is the colour of iron (II) in NH3?
Green ppt which oxidises on standing
What is the colour of iron (III) in NH3?
Red/brown ppt
What is the colour of cobalt (II) in some NH3?
Pink solution to blue ppt
What is the colour of cobalt (II) in excess NH3?
Redissolves to form brown solution that darkens on standing
What is the colour of copper (II) in NH3?
Ppt redissolves forming dark blue solution
What is the colour of Cr2O7 2-?
Orange
What is the colour of Cr 3+?
Green
What is the colour of Cr 2+?
Pale blue
What is the colour of V 2+?
Violet
What is the colour of V 3+?
Green
What is the colour of (VO) 2+?
Blue
What is the colour of (VO2) +?
Yellow
What happens to the entropy and therefore △G if a ligand is replaced by another which forms more co ordinate bonds?
- Significant increase in entropy
- And △H is negligible
- Therefore △G is very negative and reaction is feasible
What is the chelate effect?
When:
- Ligands are replaced with by another that forms more coordinate bonds
- Reaction is feasible
What does a large Kstab mean?
Complex formed is very stable
What does a small Kstab mean?
Complex formed is not very stable
Which complexes tend to have a larger Kstab?
Complexes containing:
- Bidentate ligands
- Polydentate ligands
