Module 5: Chapter 24 (Transition Elements) Flashcards
Where are d-block elements found on the periodic table?
between Group 2 and Group 13
What is the highest energy level for period 4?
from Sc to Zn 3d sub-shell has the highest energy level
What are d-block elements?
- all metals, form metallic bonds
- good conductors of heat and electricity
- high melting and boiling points
What are some uses of d-block elements?
Cu, Ni, Zn and Ag are used in coins
Fe is used to make steel used in construction and tool making
Cu is used in water pipes and electrical wiring
What is the electron configuration of chromium?
[Ar]3d5 4s1
- half filled d-subshell
What is the electron configuration of copper?
[Ar] 3d10 4s1
- fully filled d sub-shell
Why do chromium and copper have half and fully filled sub-shells?
It is believed that the half-filled or fully filled d sub-shell gives additional stability to atoms of chromium and copper
When elements between Sc and Zn form ions, are electrons lost from 3d sub-shell first?
4s empties before 3d orbitals when forming an ion (4s fills before 3d when forming an atom, first in first out)
What are transition elements?
d-block elements that form at least one ion with a partially filled d-orbital
Why are Zn and Sc not transition elements?
both only form one ion without a partially filled d-orbital
Sc3+ = 1s2 2s2 2p6 3s2 3p6 (empty d-orbitals) Zn2+ = 1s2 2s2 2p6 3s2 3p6 3d10 (full d-orbitals)
What are the properties of transition elements and their compounds?
- they can form compounds in which the transition element has different oxidation states
- they form coloured compounds
- many transition elements and their compounds can act as catalysts
Transition element property: variable oxidation states
- each oxidation state has a characteristic colour
- the number of oxidation states increases across the series to manganese and then decreases
- a species containing a transition element in its highest oxidation state is often a strong oxidising agent (e.g. manganate (VII) ion MnO4^-)
Transition element property: formation of coloured compounds
- compounds and ions of transition metals are frequently coloured
- e.g. potassium dichromate (VI) is orange and hydrated copper (II) sulfate is blue
- solid compounds can be dissolved in water to produce coloured solutions
- colour of a solution is linked to the partially filled d-orbitals of the transition metal ion
Define what a catalyst does?
A catalyst is a substance that increases the rate of a chemical reaction without itself changing. It works by providing an alternative reaction pathway of lower activation energy.
Give an example of where a heterogeneous catalyst is used in industry?
- an iron catalyst used in the Haber Process to make ammonia
- Vanadium (V) Oxide (V2O5) is used in the Contact Process (manufacture of sulfuric acid), catalyses the reaction of 2SO2 + O2 <=> 2SO3
- Nickel used in the hydrogenation of vegetable oils to make margarine
What is meant by a heterogeneous catalyst?
The catalyst is in a different state to the reactants
Transition elements property: catalysts
HOMOGENEOUS catalysts…
- Reaction between iodide ions and peroxodisulfate ions is catalysed by Fe2+(aq) ions
S2O8^2-(aq) + 2I-(aq) -> 2SO4^2-(aq) + I2(aq)
- How Fe2+ catalyses reaction…
Fe2+ reacts: S2O8^2- + Fe2+ -> 2SO4^2- + Fe3+
Fe2+ regenerated: Fe3+ + 2I- -> I2 + Fe2+
- Reaction of zinc metal with acids is catalysed by the presence of Cu2+(aq) ions
What is an orbital?
A region around a nucleus where there is a high probability of finding an electron
- an orbital can hold up to 2 electrons with opposite spin
Describe an s-orbital?
- sphere shape
- one occurs in every principal energy level
Describe a p-orbital?
- dumb-bell shaped
- 3 orbitals in the z, y and x axis
- 3 orbitals occur in energy levels except the first
What is a complex ion
A complex ion is formed when one or more molecules or negatively charged ions (ligands) bond to a central metal ion
What is a ligand?
A ligand is a molecule or ion that donates a pair of electrons to a central metal ion to form a coordinate bond or dative covalent bond
What is a coordinate/dative covalent bond?
A shared pair of electrons in which the bonded pair has been provided by one of the bonding atoms only
What is the coordination number?
The coordination number indicates the number of coordinate bonds attached to the central metal ion
What is a monodentate ligand?
Able to donate one pair of electrons to a central metal ion
What are the 5 common monodentate ligands?
Water (H2O:) neutral charge ammonia (:NH3) neutral charge chloride (:Cl-) 1- charge cyanide (:CH-) 1- charge hydroxide (:OH-) 1- charge
: = which atom the lone pair is found on
What is a bidentate ligand?
able to donate 2 pairs of electrons to a central metal ion
What are the 2 common bidentate ligands?
- Ethanedioate (oxalate), (C2O4)2-
- usually forms coordination number of 6
- the negatively charged oxygens donate lone pairs to metal ion (other two oxygens have a double bond each with a carbon) - 1,2-diaminoethane (shortened to en), H2NCH2CH2NH2
- lone pairs found on both nitrogen atoms
- coordination number is normally 6
What to remember when drawing complex ions?
- central metal ion (no charge)
- ligans (bonded to correct atom)
- 3D shape always
- lone pairs and dative bonds
- brackets with an overall charge of ion
Shape of complex ions: six coordinate complexes
- Octahedral shape
- bond angle of 90º around the central metal ion
- 6 coordinate bonds
Shape of complex ion: four coordinate complexes (tetrahedral)
- coordination number of 4
- tetrahedral shape
- bond angle of 109.5º around central metal ion
- e.g [CuCl4]2-
Shape of complex ion: four coordinate complexes (square planar complexes)
- coordination number of 4
- square planar shape
- square planar occurs in complexes involving a transition metal with 8 d-electrons in the highest energy level (e.g. platinum (II), palladium (II) and gold (III))
What is an example of a multidentate ligand?
- EDTA^4- is a hexadentate ligand, bonds to the central metal ion 6 times
- e.g. [Cu(EDTA]2-
- forms 6 coordinate bonds
What is stereoisomerism?
The same structural formula but a different arrangement of the atoms in space
What are the 2 types of isomerism complex ions can display?
- cis-trans isomerism
- optical isomerism
Describe cis-trans isomerism in square planar?
- no more than 2 identical ligands attached to the central metal ion
- cis-isomer = 2 idental groups are adjacent to each other and the coordinate bonds between the identical ligands are 90º
- trans-isomer = 2 identical groups are opposite each other and the coordinate bonds between the identical ligands are 180º
Draw cis-platin and trans-platin
[Pt(NH3)2Cl2]
cis = Cl is 90º apart
trans = Cl is 180º apart
No overall charge on ion
What is the role of cis-platin in the treatment of cancer?
- cis-platin works by forming a platinum complex inside a cell which binds to DNA and prevents the DNA of the cell from replacing
- activation of the cell’s own repair mechanism lead to apoptosis, or systematic cell death
Describe cis-trans isomerism is octahedral complexes with monodentate and bidentate ligands?
MONO…
- there must be 4 of one ligand and 2 of another
- the 2 identical ligands are in cis-form when they are at 90º and trans-form when they are 180º apart (opposite)
BI…
- 2 bidentate ligands and 2 identical ligands
- 90º apart = cis-isomer
- 180º apart = trans-isomer
What are optical isomers?
- optical isomers are stereoisomers that are non-superimposable mirror images of each other
- e.g. [Co(NH2CH2CH2NH2)2Cl2]+ only the cis-form shows optical isomerism as the mirror image forms are non-superimposable (when the images are overlaid it does not overlap)
- this can occur with 2 bidentate ligands with 2 mondentate ligands or with 3 identical bidentate ligands around central ions in octahedral complexes
Cu2+
- aqueous formula?
- solution colour?
- precipitate colour with NH3?
- precipitate colour with NaOH?
[Cu(H2O)6]2+ forms pale blue solution
Adding NH3 = pale blue precipitate of Cu(OH)2
In excess ppt dissolves forming [Cu(NH3)4(H2O)2]2+ dark blue solution
Adding NaOH = pale blue precipitate of Cu(OH)2
Fe2+
- aqueous formula?
- solution colour?
- precipitate colour with NH3?
- precipitate colour with NaOH?
[Fe(H2O)6]2+ forms a pale green solution
Adding NH3 = green ppt of Fe(OH)2
Iron (II) hydroxide will slowly oxidise into iron (III) hydroxide in air (an orange-brown ppt)
Adding NaOH = green ppt of Fe(OH)2
Iron (II) hydroxide will slowly oxidise into iron (III) hydroxide in air (an orange-brown ppt)
Fe3+
- aqueous formula?
- solution colour?
- precipitate colour with NH3?
- precipitate colour with NaOH?
[Fe(H2O)6]3+ forms a yellow solution
Adding NH3 = orange-brown ppt of Fe(OH)3
Adding NaOH = orange-brown ppt of Fe(OH)3
Mn2+
- aqueous formula?
- solution colour?
- precipitate colour with NH3?
- precipitate colour with NaOH?
[Mn(H2O)6]2+ forms a pale pink solution
Adding NH3 = light-brown ppt Mn(OH)2
Adding NaOH = light-brown ppt Mn(OH)2
Cr3+
- aqueous formula?
- solution colour?
- precipitate colour with NH3?
- precipitate colour with NaOH?
[Cr(H2O)6]3+ forms a violet solution
Adding NH3 = green precipitate of Cr(OH)3
In excess ppt dissolves forming a purple solution of [Cr(NH3)6]3+
Adding NaOH = green precipitate of Cr(OH)3
In excess ppt dissolves into a dark green solution of [Cr(OH)6]3-
What is the reaction of ammonia with water?
NH3(aq) + H2O(l) <=> NH4+(aq) + OH-(aq)
The hydrated copper(II) ion is classed as a complex but he hydrates sodium ion is not. Explain why the hydrated sodium ion is not considered to be a complex ion
- Oxygen atoms in water molecules have a partial negative charge
- These form electrostatic attractions with sodium ion (ion-dipole bond) not a dative covalent bond
Describe the structure of RBC
- RBCs contain haemoglobin which are made up of 4 protein chains each of which has a haem group within the structure
- Haem group is a complex ion with an Fe2+ central metal ion
- This can bind to O2 gas in the lungs becoming oxyhaemoglobin
Describe the haem group acting as a complex ion
- Lone pair on 4 nitrogen form a coordinate bond with Fe2+
- Iron can accept 2 more lone pairs, one above and below the plane
- one of these comes from a nitrogen of an amino acid
- the other is from an oxygen molecule (O2)
- the O2 can be replaced by a water molecule (each easily replace each other)
- Complex has a coordination number of 6
What is the effect of CO?
- Carbon Monoxide bonds irreversibly to haemoglobin (carboxyhaemoglobin) making it incapable of binding with any more oxygen
- If the carboxyhaemoglobin concentration becomes high enough the result is death
What is ligand substitution?
A ligand substitution reaction is one in which one ligand in a complex ion is replaced by another ligand.
Describe the ligand substitution of [Cu(H2O)6]2+ and NH3
[Cu(H2O)6]2+ + 4NH3 -> [Cu(H2O)2(NH3)4]2+ + 4H2O
pale blue solution -> dark blue solution (caused by complex ions)
Ammonia is in excess
Both ions are in complex shape and second ion is in trans form (H2O 180º)
- forms a blue precipitate first which then dissolves in excess to the dark blue solution
Describe the ligand substitution of [Cu(H2O)6]2+ and Cl-
[Cu(H2O)6]2+ + 4Cl- <=> [CuCl4]2- + 6H2O
pale blue solution <=> yellow solution (caused by complex ions)
equilibrium reaction
octahedral shape <=> tetrahedral shape
Cl- comes from concentrated hydrochloric acid
Describe the ligand substitution of [Cr(H2O)6]3+ and NH3
[Cr(H2O)6]3+ + 6NH3 -> [Cr(NH3)6]3+ + 6H2O
violet solution -> purple solution
ammonia is in excess
both ions are in octahedral shape
Describe the ligand substitution of [Cr(H2O)6]3+ and SO4^2-
[Cr(H2O)6]3+ + SO4^2- -> [Cr(H2O)5 SO4]+ + H2O
pale purple solution -> green solution
