Chapter 24 Flashcards
Physical properties of d block elements
High melting points and boiling points
Shiny in appearance
Conduct both electricity and heat
Transition elements
D block elements that form at least one stable ion with a partially filled d-orbital
What two d block elements are not transition elements?
Scandium and zinc are d block elements but do not match the definition and are thus not classified as transition elements
Scandium
Only forms Sc3+ by loss of two 4s electrons and one 3d electron thus highest energy electron is in 3p subshell/orbital
Zinc
Only forms the Zn2+ ion by the loss of its two 4s electrons thus has a fully filled 3D subshell (full d-orbitals)
Properties of transition metals?
They form compounds in which the transition element has different oxidation states
They form coloured compounds
The elements and their compounds can act as catalysts
Variable oxidation states
Transition elements form compounds with more than one oxidation state - number of oxidation states increases across the transition elements series to manganese and then decreases - all of the transition elements form compounds with an oxidation number of +2
Species containing transition metal in highest oxidation state?
A strong oxidising agent
Potassium dichromate (vi)
Bright orange
Cobalt (ii) chloride
Pink-purple
Nickel (ii) Sulfate
Green
Copper (ii) Sulfate
Blue
What is colour of transition element solution linked to?
Partially filled d-orbitals of the transition metal ion - colour varies with different oxidation states
Fe 2+
Pale green
Fe 3+
Yellow
Cr 3+
Green
Cr +6
Yellow
Haber process
Manufacture of ammonia from nitrogen and hydrogen
CATALYSED BY A FINELY DIVIDED IRON CATALYST
Contact process
Sulfur trioxide from oxidation of sulfur dioxide - catalysed by vanadium oxide
Hydrogenation of vegetable fats in manufacture of margarine?
Uses nickel as the catalyst
Catalytic decomposition of hydrogen peroxide forming oxygen
Uses manganese oxide as the catalyst
2H2O2 -> 2H2O + O2
Example of homogenous catalysts
Catalyst is in the same physical state as the reactants - reaction between iodide ions and peroxodisulfate ions is catalysed by Fe2+ (aq) ions
Overall reaction homogenous catalyst
S2O82- (aq) + 2I- (aq) -> 2SO42- (aq) + I2 (aq)
When peroxodisulfate ions is carried out with a trace of starch
A blue-black colour forms ; if this experiment is repeated with a small a Fe2+ - blue black solution forms much more quickly demonstrating the catalytic action of transition metal ion
Fe2+ disulfate?
Forms Fe3+
Vital property of d-block elements?
Ability to form complex ions - blue solution is formed containing complex ion [Cu(H2O)6]2+
How can complex ions be formed?
Not restricted to d-block elements - other elements such as aluminium can also form complex ions
What is a ligand?
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 ligand?
It 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 dative covalent bond/coordinate bond?
Special kind of covalent bond which is formed when one of the bonded atoms provides both of the electrons for the shared pair - coordination number indicates the number of coordinate bonds attached to the central metal ion
Overall charge of complex ion
Sum of the charges on the central metal ion and any ligands present
Water acting as a ligand?
Each water molecule donating a lone pair of electrons from the oxygen atom to the central metal ion to form a coordinate bond
Monodentate ligand
A ligand that is able to donate one pair of electrons to a central metal ion
Examples of monodentate ligands
Water/ammonia/halides/cyanide
Bidentate ligands
Donate two lone pairs of electrons to the central metal ion forming two coordinate bonds
Common bidentate ligands?
1,2 - diaminoethane and ethanedioate
1,2-diaminoethane
Each nitrogen atom donates a pair of electrons to the central metal ion forming a coordinate bond
Ethanedioate ion
Each negatively charged oxygen atom donates a lone pair of electrons to the central metal ion
6 coordinate complexes?
With coordination number 6 an octahedral shape is produced - bond angles around central ion being 90 degrees
Complexes with coordination number 4
Either tetrahedral or square planar
Tetrahedral shape
Common of the two shapes with bond angles of 109.5 around the central metal ion
When does square planar shape occur?
Occurs in complex ions of transition metals with 8 d electrons in the highest energy d sub-shell ; platinum , palladium and gold fall in this category and tend to form square planar complexes
Square planar
Ligands are arranged with two going out and two going in
90 degrees bond angle
Platinum charge
2+
Palladium charge
2+
Gold charge
3+
For complex ions type of stereoisomerism?
Depends on number and type of ligands that are attached to central metal ion
4 and 6 coordinate complex ions containing two different monodentate ligands show cis-trans isomerism
6 coordinate complex ions containing monodentate and bidentate ligands can show both cis trans and optical isomerism
Cis trans isomerism in complex ions?
Cis-trans isomerism occurs in some square planar and octahedral complex ions
Cis-trans isomerism square planar
Simplest example of cis-trans isomerism is found in 4 coordinate square planar complexes that have no more than two identical ligands attached to the central metal ion
Cis square planar isomer?
Two identical groups are adjacent to each other - one going inside and one going outside (next to each other vertically)
Trans isomer
Two identical groups are diagonally opposite each other - coordinate bonds are 180 degrees apart
Cis-trans in monodentate ligands?
Octahedral complexes containing 4 of one type of ligand and two of another type of ligand also exist ast cis-trans isomers
Cis [Co(NH3)4Cl2]+
Chloride ligands are next to each other - 90 degrees apart (different bonds - one in the plane and the other going out)
Trans [Co(NH3)4Cl2]+
Chloride ligands are vertically opposite each other - 180 degrees apart - both ligands are in the same plane
Colours of [Co(NH3)4Cl2]+
Cis = violet
Trans = green
Bidentate ligands cis-trans stereoisomerism
THERE SHOULD BE TWO OF THE SAME LIGANDS NEXT TO EACH OTHER (DIFFERENT PLANES) - 90 DEGREES APART FOR CIS AND 180 FOR TRANS (SAME PLANE)
Optical isomers
Non-superimposable mirror images of each other
Optical isomers of octahedral complexes?
Only occurs in octahedral complexes containing two or more bidentate ligands
Can only form enantiomers of cis isomers
Optical isomers
Can also be seen in complexes containing 3 bidentate ligands
1,2-diaminoethane
Such a common bidentate ligand that it is often abbreviated to “en”
Ligand substitution reaction
One ligand in a complex ion is replaced by another ligand
Reactions of aqueous copper (ii) ions
Copper sulfate is dissolved in water and [Cu(H2O)6]2+ forms
This is a pale blue solution which changes colour to form a dark blue solution when 4NH3 is added and replaces 4 of the H2O ligands producing 4H2O as a by-product
Breakdown of addition of 4NH3 to hexaaquacopper
Add the ammonia drop-wise to the solution
- pale blue precipitate of Cu(OH)2 is formed in the first stage of the reaction
- the precipitate then dissolves in excess ammonia to form a dark blue solution
Ligand substitution with chloride ions?
Concentrated HCl can be used as a source of chloride ions - excess is added - the pale blue solution changes colour to form a yellow solution which is another example of a ligand substitution reaction as 6 water ligands have been replaced with 4 chloride ligands
Observations of ligand substitution of chloride ions?
Intermediate green solution is formed but this is just the result of the yellow solution mixing with the blue solution to give a green colour as the reaction proceeds
Hexaaquacopper to tetrachlorocopper?
Change in coordination number : 6 to 4
Change in colour : pale blue to yellow solution
Change in shape : octahedral to tetrahedral
Reasoning behind number of chloride ligands?
They are larger in size/bulkier than water ligands so fewer chloride ligands can fit around the central Cu2+ ion
What is chromium potassium Sulfate called?
Chrome alum
When chromium potassium Sulfate is dissolved in water?
Complex ion [Cr(H2O)6]3+ is formed - this is pale purple solution
When chromium iii Sulfate is dissolved in water?
Green solution containing chromium iii is formed - in this case it is the complex ion [Cr(H2O)5SO4]+ where ONE OF THE WATER LIGANDS IS REPLACED WITH SO4
Oxidation state of chromium ions?
+3
Equation for chromium ligand substitution reaction with ammonia?
[Cr(H2O)6]3+ + 6NH3 -> [Cr(NH3)6]3+ + 6H2O
Where hexaaquachromium is violet and turns purple
Breakdown of reaction of ammonia with (cr(H2O)6) 3+
When the ammonia is added drop-wise to the chromium iii solution it takes place in two steps
STEP 1 : grey-green precipitate of cr(oh)3 is formed
STEP 2 : precipitate dissolves in excess ammonia to form the complex ion (cr(NH3)6)3+
Carbon monoxide + Fe2+
Forms carboxyhaemoglobin - ligand substitution reaction takes place where the oxygen in haemoglobin is replaced by carbon monoxide as carbon monoxide binds to haemoglobin more strongly than oxygen so a small concentration of carbon monoxide can prevent a large proportion of haemoglobin molecules from carrying oxygen
Carboxyhaemoglobin?
Bond is so strong that this process is irreversible
Precipitation reaction
When two aqueous solutions containing ions react together to form an insoluble ionic solid called a precipitate
Cu2+ reaction with NaOH
Blue solution forms a blue precipitate of copper hydroxide and PRECIPITATE IS INSOLUBLE IN EXCESS NAOH
Fe2+ with NaOH
Pale green solution reacts to form a green precipitate of Iron (ii) hydroxide - precipitate is insoluble in excess sodium hydroxide but turns brown at its surface on standing in air as iron (ii) is oxidised to iron (iii)
Fe3+ with NaOH
Pale yellow solution reacts to form an orange-brown precipitate of iron(iii) hydroxide - precipitate is insoluble in excess sodium hydroxide
Mn2+ and NaOH
Pale pink solution reacts to form a light brown precipitate of manganese (ii) hydroxide which darkens on standing in air
PRECIPITATE IS INSOLUBLE IN EXCESS NAOH
Reaction of Cr3+ with NaOH
Violet solution reacts to form a grey-green precipitate of chromium (iii) hydroxide
Precipitate is SOLUBLE IN EXCESS NAOH forming a dark green solution
Chain of reaction Cr3+ and NaOH
Cr3+ -> Cr(OH)3 -> [Cr(OH)6]3-
Copper hydroxide precipitate and ammonia?
Dissolves in excess ammonia to form a deep blue solution with the formula [Cu(NH3)4(H2O)2]2+
Chromium hydroxide precipitate + ammonia
Chromium hydroxide is a green precipitate which dissolves in excess ammonia to form [Cr(NH3)6]3+ which is a purple solution
Fe2+/Fe3+/Mn2+ + ammonia
All react with an excess of aqueous ammonia in the same way as they react with aqueous sodium hydroxide - forming precipitates of iron (ii and iii) hydroxide and manganese hydroxide - no further reaction with aqueous ammonia so these precipitates do not dissolve
Fe2+ + MnO4- ions
Fe2+ is oxidised to Fe3+
MnO4- is reduced to Mn2+
Solution containing MnO4- is purple and is decolourised by Fe2+ ions to form a colourless solution containing Mn2+ ions
Fe3+ to Fe2+
When a solution of Fe3+ reacts with iodide ions the orange brown Fe3+ ions are reduced to pale green Fe2+ ; this colour change is obscured by the oxidation of iodide ions to form iodine which has a brown colour
2Fe3+ + 2I- -> 2Fe2+ + I2
2Fe3+ is orange brown
Fe2+ is pale green
I2 is brown
Electrode potential for redox reactions?
More positive the electrode potential value - the more likely the species to undergo reduction and shift to the right, gaining electrons
How are cr2o72- ions reduced to cr3+?
Orange to green colour - reduced by the addition of zinc - with an excess of zinc, chromium iii ions are reduced further to chromium ii which is pale blue colour
Oxidation of cr3+ to cro42-
Hot alkaline hydrogen peroxide h2o2 is a powerful oxidising agent and can be used to oxidise chromium iii to chromium 6
Overall equation for oxidation of cr3+ to cro42-
3H2O2 + 2Cr3+ + 10OH- -> 2CrO42- + 8H2O
Reduction of Cu2+ to Cu+
When they react with excess iodide ions a redox reaction occurs and I- is oxidised to brown I2 while a white precipitate of copper iodide is also created
Equation for reduction of cu2+ to cu+
2Cu2+ + 4I- -> 2CuI + I2 (s)
Pale blue
Copper iodide is a white precipitate
Iodine is brown
Disproportionation of Cu+ ions
Solid copper (I) oxide reacts with hot dilute H2SO4 - a brown precipitate of copper is formed together with a blue solution of copper (ii) Sulfate
Disproportionation of Cu+ ions equation
Cu2O + H2SO4 -> Cu + CuSO4 + H2O
Copper goes from +1 to + 2
-1 to 0
Copper solid
Brown solid
Copper Sulfate
Blue solution
Ammonium ions + OH-
NH4- + OH- -> NH3 + H2O
Ammonia is evolved it will turn damp red litmus paper blue
Halide ions solubility in NH3
Cl- soluble in dilute NH3
Br- soluble in concentrated nh3
I- insoluble in NH3
